Radio -Television -Electronics

Dictionary

NATIONAL. RADIO INSTITUTE

WASHINGTON, D. C.

IX -3

11

HOW TO USE THIS DICTIONARY

This book is a reference text and should be used as one. Donot read it as you would a Lesson, nor try to memorize theterms and their definitions.

Remember, a dictionary is not an encyclopedia, so do notexpect to find complete explanations that belong in the Les-sons. Non -technical words are not defined since they can befound in an ordinary dictionary. Where a word has two mean-ings, technical and non -technical, only the technical definitionis given. (You might see a ghost, for example, on a televisionscreen as well as in a haunted house. Only the first kind ofghost is defined here.)

Where there are two or more names for the same thing, thedefinition will be found under the most commonly used term,and the others will be cross-referenced to it in italic (slant-ing) type. Terms usually abbreviated have their abbrevia-tions printed after them in parentheses. In addition, a list ofall commonly used radio abbreviations will be found onpages 93-95, and a table of radio symbols is printed onpage 96.

This dictionary has been completely rewritten to include thelatest technical developments in radio, television, and elec-tronics. Many of the terms here you may never run across,but complete coverage is provided in case you ever need it.Make use of it. It will save you time and trouble.

FM20M75I

COPYRIGHT 1911 BY NATIONAL RADIO INSTITUTE

WASHINGTON, D. C.

Printed in U.S.A.

Radio -Television -Electronics Dictionary

Aabampere. The unit of current flow in the ab-

solute system of electromagnetic units (emu).One abampere is equal to 10 amperes.

A battery. The source of filament current for thetubes in a battery -operated vacuum -tube cir-cuit.

abcoulomb. The unit of quantity of electricity inthe absolute system of electromagnetic units(emu). One abcoulomb is equal to 10coulombs.

aberration. A lens defect in which the light rayscoming from a single point are brought todifferent focal points. See chromatic aberra-tion and spherical aberration.

abfarad. The unit of capacity in the absolutesystem of electromagnetic units (emu). Oneabfarad is equal to 1,000,000,000 farads.

abhenry. The unit of inductance in the aboslutesystem of electromagnetic units (emu). Oneabhenry is equal to .000000001 henry.

abohm. The unit of resistance in the absolutesystem of electromagnetic units (emu). Oneabohm is equal to .000000001 ohm.

AB power pack. A combination of batteries orother power -supplying devices in a singlehousing, used to supply filament and plate

portable sets.

abrasive. A grinding or polishing material,specifically that incorporated in some phono-graph records for the purpose of shaping theneedle point to fit the groove properly.

abscissa. The coordinate value specifying dis-tance in a horizontal direction from the ver-tical reference line on a graph, Also, the hori-zontal reference line along which these valuesare indicated.

absolute units. Units of measurement derivedfrom the centimeter -gram -second (cgs) sys-tem of specifying length, mass, and time.

absolute value. The value of a number withoutregard to sign. Thus, the absolute values of+9 and -9 are both 9. In algebraic expres-sions vertical lines on each side of a quantityare used to specify that the absolute value isto be used. Example: the absolute value of xis written I x I.

absorption. Dissipation or loss of electromagneticenergy (radio waves) or acoustic energy(sound waves) in the medium through whichthe energy travels, or the extraction of elec-trical energy from one circuit by anothercoupled to it.

absorption coefficient. A measure of the ability ofa material to absorb energy, especially fromsound waves.

absorption modulation. Modulation produced byabsorption of signal power from the antenna

rf system of a transmitter by a closelycoup, 1 of system.

absorption trap. A tuned circuit coupled to an-other circuit for the purpose of absorbing andattenuating undesired signals.

1

absorption wavemeter. A device for measuringthe wavelength or frequency of a radio wave,loosely coupled to a signal source so that itextracts enough energy to operate an indi-cator.

abvolt. The unit of potential in the absolute sys-tem of electromagnetic units (emu). One ab-volt is equal to .00000001 volt.

accelerating electrode. An electrode in cathode-ray and vacuum tubes operated at a raga posi-tive potential to increase the velocity of theelectrons.

acceleration. The rate of increase of velocity.accentuation. The emphasizing of a frequency

or range of frequencies in an amplifier orother electronic device; applied particularlyto the increased amplification given the high-er audio frequencies in FM transmitters.

acceptor circuit. A circuit offering minimum im-pedance to a desired frequency or band offrequencies, and high impedance to all otherfrequencies.

ac -dc receiver. A receiver that will operate fromeither an ac or a dc power source. It has nopower transformer. A universal receiver.

acetate disc. A disc for instantaneous recording,resembling a phonograph record, whose re-cording surface is an acetate plastic.

ac generator. Any device that produces an acvoltage, such as an oscillator or a dynamo -electric generator.

achromatic lens. A combination of two or morelenses, the curvature of one serving to correctthe chromatic aberration of the others.

Courtesy RCAAcorn Tubes

acorn tube. A small tube resembling an acorn insize and shape, designed to have low internalcapacities, thus permitting its use in ultra-high -frequency applications, up to about 400megacycles.

acoustic. Pertaining to sound and hearing.acoustic feedback. Transfer of energy from the

sound waves coming from the loudspeaker toany preceding part in the same amplifyingor broadcasting system in such a way thatthe current in the circuit is modulated, pro-ducing howling or squealing.

acoustic labyrinth. A winding passageway de-signed to lengthen the sound path from thefront to the back of a loudspeaker. It lowersthe cut-off frequency and extends the bassresponse.

acoustics. The science of sound. The study of thecause and effect of audible vibrations. Alsothe characteristics of a room or space that af-fect sound propagation and sound travel.

acoustimeter. A device for the electrical measure-ment of sound, having an output indicatorcalibrated in db or in units of sound intensity.A sound -lever meter.

ac plate current (Ip). The alternating componentof the plate current of a tube. It is equal tothe ac plate voltage divided by the total im-pedance in the circuit.

ac plate resistance (Rp). The opposition offeredby the plate -cathode path of a tube to the flowof alternating current. With no load in thecircuit, it is equal to the change in plate volt-age divided by the resulting change in platecurrent, or to the ac plate voltage divided bythe ac plate current.

ac receiver. A receiver designed to operate onlyfrom an ac power source.

active lines. The television image lines actuallyvisible on the screen, those of the 525 imagelines not blanked out.

acute angle. An angle that is less than a rightangle (less than 90°).

adapter. A device permitting the use of a sub-stitute part or auxiliary apparatus, or for con-verting test equipment, or for converting asignal to a different frequency band, withoutchange in the original equipment.

Adcock antenna. Two or more vertical conductorsfor reception or transmission of radio waves,arranged so that the interconnecting hori-zontal wires have little or no pickup.

adjacent -channel interference. Interference origi-nating in the channels on either side of thatto which the receiver is tuned. Loosely, inter-ference from any channel near the desiredone.

adjacent -channel selectivity. The ability of a re-ceiver to reject the signals of stations oneither side of the channel carrying the de-sired signal.

adjacent side. In a right triangle, the side of anacute angle that is between that angle andthe right angle.

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11111111111 11111

Adjustable Resistor

adjustable resistor. A wire -wound resistor havinga movable tap that can be clamped at any de-sired point along the resistor.

adjustable voltage divider. A wire -wound resistorhaving three or more terminals, at least one ofwhich is movable to permit its being clamped

at any desired point to adjust the voltage di-vision.

admittance (Y). A measure of the ease with whichan alternating current flows in a circuit. Thereciprocal of impedance, measured in mhos.The word mho is ohm spelled backwards, in-dicating it is a reciprocal.

advance ball. The rounded support (often sap-phire) which rides on the disc adjacent to therecording stylus of a sound recorder. It main-tains even depth of cut by correcting for smallirregularities in the surface of the disc.

aerial. An antenna.afterglow. The continued emission of light by a

phosphorescent material after excitationceases. Persistence, phosphorescence.

air -cell battery. A non -rechargeable wet -cell bat-tery delivering about 2.5 volts when new, usedchiefly in 2 -volt battery -operated home re-ceivers. Its carbon electrodes are porous, andabsorb oxygen from the air for depolarizationpurposes.

air condenser. A condenser having air as its di-electric.

air core. A magnetic circuit consisting only ofair and other non-metallic materials.air -core transformer. A transformer having a

core (magnetic circuit) of air or other non-metallic materials, so that the magnetic linesof force travel only through these non-mag-netic materials.

air gap. A path for electrical or magnetic energythrough air between two objects, as betweenthe electrodes of a spark gap or the core sec-tions of an iron -core transformer.

airplane dial. Popular name for a circular radioreceiver dial with a rotating pointer, re-sembling the dials and pointers of airplaneinstruments.

airport runway beacon. A radio signal used toindicate the approaches to an airport. Also,the transmitter producing such a signal.

Air Traffic Control (Aid). A system establishedby the CAA for issuing information and in-structions to aircraft. At or near an airport itis called Airport Traffic Control, and alongthe airways, Airways Traffic Control.

Alexanderson alternator. A high -frequency ac dy-namoelectric generator used in the early daysof radio to produce radio waves.

algebra. A continuation of arithmetic in whichletters and symbols are used to represent defi-nite quantities whose actual values may ormay not be known. Example: in the equation2x=10, x must equal 5. A literal algebraicexpression contains general numbers or let-ters. Example: 271-fL represents the numberof ohms of inductive reactance; I2R representsthe number of watts of power.

algebraic subtraction. To subtract one numberfrom another algebraically, change the sign ofthe number subtracted (the subtrahend), thenadd algebraically. Examples : To subtract 7from 10, change 7 to -7 and add algebraicallyto get 3. To subtract 14 from -20, change 14to -14, then add -14 and -20 algebraicallyto get -34. To subtract -7 from 40, change-7 to 7 and add, getting 47.

algebraic sum. The sum obtained by addingnumbers with regard for their signs. To addnumbers having like signs, find the sum oftheir absolute values and place the commonsign in front of the result. Example : The

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algebraic sum of -3, -5, -1 and -10 is -19.To add two numbers having unlike signs, findthe difference of their absolute values, andplace the sign of the larger absolute value infront of the result. Example: The algebraicsum of 7 and -3 is 4; the algebraic sum of-33 and 11 is -22. When three or more num-bers, some having different signs, are to beadded algebraically, find the sum of the posi-tive numbers first, then find the sum of thenegative numbers. Finally, add the partialsums algebraically to get the total algebraicsum. Example: The algebraic sum of +17,-3, -10, and +4 is the algebraic sum of 21and -13, which is 8.

align. To adjust tuning circuits so they respondto the desired frequency or band of frequen-cies. Also, to line up holes in two or moreparts so a bolt can be passed through theholes, or to line up parts by positioning themin a straight line.

Aligning Tools

aligning tool. A small screwdriver or socketwrench, constructed partly or entirely fromnon-metallic materials, used for making neu-tralizing or aligning adjustments in radio re-ceivers. The use of non-metallic materialseliminates body capacity that would affect theaccuracy of the adjustments if an ordinarymetal wrench or screwdriver were used.

alignment. The process of adjusting the tuningcircuits in a receiver or transmitter so they re-spond to the desired frequency or band of fre-quencies.

alignment chart. A chart giving manufacturer'salignment instructions.

alive. Energized by being connected to an oper-ating voltage source.

alligator clip. A long -nose clip with spring -controlled jaws and meshing teeth, used ontest leads for making quick temporary con-nections.

all -metal tube. A vacuum or gaseous tube havinga metal envelope or housing, with electrodeconnections being made through glass beadsfused into the metal envelope. Usually calleda metal tube.

alloy. A mixture of two or more metals. Forexample, bronze is an alloy of copper and tin.

all -wave antenna. A receiving antenna designedto pick up stations over a wide range of car-rier frequencies, including short-wave bandsas well as the broadcast band.

all -wave oscillator. An an -wave signal generator.

all -wave receiver. A radio receiver capable ofreceiving stations on all commonly used broad-cast bands. The most common all -wave re-ceivers have a range from 500 kc to 30 mc.

all -wave signal generator. A test instrumt_capable of generating any of the radio -fre-quency signals needed in aligning or servic-ing all -wave receivers (approximately 100kc to 20,000 kc).

Alnico. An alloy of iron, aluminum, nickel, andcobalt, that holds magnetism indefinitely,used in permanent magnets for loudspeakers,motors, dynamotors, meters, and motor -gen-erators. There are several kinds of Alnico,differing in magnetic characteristics, identi-fied by a number, as Alnico III, Alnico V.

alternating current. An electric current that re-verses direction of flow at regular intervals.

alternation. One half of a cycle, consisting of acomplete rise and fall of current in one direc-tion. Thus, 60 -cycle alternating current has120 alternations per second.

alternator. A dynamoelectric generator for pro-ducing ac voltages.

aluminized -screen picture tube. A cathode-ray pic-ture tube iff which a thin layer of aluminumhas been deposited on the back of the fluores-cent surface to improve the brilliance of theimage and prevent ion -spot formation.

aluminum. A metal extensively used in radio forshielding purposes, for foil plates and hous-ings of electrolytic condensers, for the platesof gang tuning condensers, and for chassisand panel construction.

amateur. Any person who operates and experi-ments with short-wave transmitters as ahobby rather than for profit. Often called a"ham."

amateur bands. Bands of frequencies assigned toradio amateurs.

amateur operator. A person holding a licenseauthorizing him to operate licensed amateurstations.

amateur -station call letters. Identifying call sig-nal assigned to a licensed amateur operator.Amateur calls in a given country begin with aone- or two -letter prefix (W for U.S., and Kfor U.S. possessions), followed by a location -indicating numeral and two or more addi-tional letters.

ambient temperature. The temperature of the airimmediately surrounding a radio part.

American Morse Code. A dot -and -dash code com-monly used for telegraphic communicationsover wires. It differs considerably from theInternational Morse Code used in radio.

American Radio Relay League (A.R.R.L.). An as-sociation of amateur radio operators and otherpersons interested in amateur radio.

American Wire Gauge. The gauge in common usein the U.S. for designating wire sizes (diam-eters). It has numbers ranging from 0000 asthe larget size to 40 and higher for the small-est sizes. Formerly called Brown and Sharpegauge (B. & S. gauge).

ammeter. An instrument used for measuring cur-rent flow in amperes.

amorphous. Uncrystallized.

ampere (amp). The practical unit of electriccurrent flow. The current that will flow if aone -ohm resistance is connected to a one -voltsource. The movement of approximately 6,280,-000,000,000,000,000 electrons past a given pointin a circuit in one second.

ampere -hour. A current of one ampere flowing forone hour; a unit used chiefly to indicate the

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amount of electrical energy a storage batterycan deliver before it needs recharging.

ampere -hour meter. An instrument that indicatesor records the number of ampere -hours of en-ergy drawn from a storage battery.

ampere -turn. A unit of magnetomotive force, orthe strength of the magnetic field produced bya coil. The number of ampere -turns is equalto the coil current in amperes multiplied bythe number of turns in the coil. One ampere -turn is equal to 1.257 gilberts.

Amphenol. A plastic material used for insulation,especially at high frequencies.

amplidyne. A motor generator used to amplifythe effect of a low -current control system. Thefield excitation of the amplidyne generator isvaried by the control, and the amplidyne out-put energizes the field of the controlled gen-erator.

amplification. The process of increasing the cur-rent, voltage, or power of a signal by usingtransformers, tuned circuits, or vacuum tubes.

amplification factor (O. A rating indicating thetheoretical maximum amplification that can beprovided by a given vacuum tube. It is equalto the ratio of the plate -voltage change to thegrid -voltage change needed to produce the samechange in plate current when a tube has noload.

amplifier. A device whose output is an enlargedreproduction of its input.

amplifier operating angle. That part of the gridsignal voltage cycle during which plate cur-rent flows.

amplify. To increase; to enlarge.of variation of a quan-

tity from a reference value, usually zero. Theamount of vertical displacement above or be-low a horizontal reference line on a graph.Also, the displacement of a phonograph recordgroove from its average or unmodulated posi-tion.

amplitude distortion. Distortion that occurs whenthe changes in the current or voltage outputof a circuit are not exactly proportional atevery instant of time to the input current orvoltage changes. Amplitude distortion resultsin the production of harmonics not present inthe original signal.

amplitude -frequency -response characteristic. Seefrequency response.

amplitude modulation (AM). A system of broad-casting, in which the amplitude of the trans-mitted signal varies in accordance with the in-stantaneous amplitude of the intelligence sig-nal, at a rate corresponding to the frequencyof the intelligence signal. This process pro-duces sideband frequencies above and belowthe assigned carrier frequency.

amplitude separation. Separation of two or moresignals of different amplitudes by arranging acircuit to pass signals that are either aboveor below a predetermined level. Specifically,separation of the synchronizing signal fromthe video component of a TV signal.

amplitude separator. The clipper or sync separa-tor stage in a television receiver.

amplitude -suppression ratio. A measure of the abil-ity of an FM receiver to limit or remove AMvariations. The ratio of the undesired AM out-put to the desired FM output.

angle. The figure formed when two straight

lines meet at a point. The lines are called thesides of the angle, and the point is called thevertex. An acute angle is less than 90°. Aright angle is 90°. An obtuse angle is morethan 90°.

angle, electrical. See electrical angle.

angle of beam. The angle enclosing the greaterpart of the energy transmitted from a direc-tional antenna.

angle of deflection. In a cathode-ray tube, theangle between the two positions of maximumdeflection of the electron beam.

angle of divergence. In a cathode-ray tube, theangle between the deflected electron streamand a longitudinal line through its center.

angle of incidence. The angle between a ray oflight falling on a surface and the perpendicu-lar to the surface at that point.

angle of lag. The angle by which a current orvoltage lags behind another current or voltage.See phase angle.

angle of lead. The angle by which a current orvoltage leads another current or voltage. Seephase angle.

angle of radiation. The angle between the earthand the strongest part of the wave radiatedfrom a transmitting antenna.

angle of refraction. The angle formed with re-spect to the normal when a ray of light passesfrom one medium to another.

angstrom unit (A). A unit of wavelength meas-urement equal to one hundred -millionth of acentimeter. The wavelength of visible light isbetween 4000 and 7000 angstrom units.

angular frequency (a). Rate of vibration or rota-tion measured in radians per second. Angularfrequency is 27r (6.28) times the number of vi-brations or cycles per second.

angular phase difference. The phase difference ex-pressed in radians or degrees.

angular velocity: The speed of a rotating bodymeasured by an angle whose vertex is the cen-ter of rotation, and through which any pointof the body moves in a given time. The angu-lar velocity of a current or voltage is equal to27r (6.28) times frequency.

anion. An electro-chemical term for a negativeion that moves toward the anode.

annealing. A process of softening metals by firstheating and then cooling gradually.

annular. Ring -shaped.

anode. A tube electrode, commonly called theplate, and usually at a high positive potentialwith respect to the cathode. Identified on dia-grams by the letter P.

anode strap. A metallic connector betweenselected anode segments of a multicavity mag-netron.

antenna. A metallic structure or an arrangementof conducting wires or rods for picking up orradiating rf waves. An aerial.

antenna array. Two or more antennas coupledtogether so as to improve transmission or re-ception in a desired direction.

antenna coil. The coil in a receiver through whichthe antenna current flows. usually directly con-nected to the antenna and ground terminals.

antenna coupler. A device in a transmitter for4

transferring rf energy from the final plate tankto the antenna. It may also serve to match theplate -tank impedance to the impedance of thetransmission line.

antenna current. The current flowing in the an-tenna.

antenna effect. The error in the direction -indicat-ing characteristic of a loop antenna due tocapacity between the antenna and ground. Inradio direction -finders, the antenna effect iscancelled out by the balancer.

antenna form factor. The ratio of the effectiveheight of an antenna to its actual physicalheight.

antenna gain. The effectiveness of an antenna ina particular direction as compared to somestandard antenna. The ratio of the power thatmust be supplied to the given antenna to thatsupplied a standard antenna to produce thesame field strength in a desired direction. An-tenna gain in db is equal to 10 times the log ofthis power ratio.

antenna power. The product of the square of theantenna current and the antenna resistance atthe point where the current is measured.

antenna resistance. The total resistance of thetransmitting antenna system at the operatingfrequency calculated at the point of maximumcurrent.

anti -capacity switch. A switch designed withminimum capacity between the switch contactsor terminals.

antilog. Antilogarithm.

antilogarithm. The number corresponding to alogarithm. Usually written antilog. Example:The logarithm of 87.9 is 1.9440, and 87.9 is theantilog of 1.9440.

Courtesy JFD Mfg. Co.Antenna Array

antinode. In a graphical representation of awave, the point of maximum amplitude. Thetype of antinode is usually specified, sincethere can be antinodes of voltage, current,pressure, velocity, etc.

anti -resonant circuit. A parallel -resonant circuit.

aperiodic antenna. An antenna with a constant

impedance over a wide range of frequencies.aperiodic circuit. A circuit with no definite time

period of oscillation because its resistance islarge enough to prevent natural oscillations,or because its capacity and inductance are ofsuch values that they will not resonate In thetuning range.

aperture. A hole in a plate or other device usedto control the diameter or position of an elec-tron beam or a light beam.

aperture compensation. Reduction of aperturedistortion by emphasizing the high -frequencycomponents of the picture signal.

aperture distortion. Attenuation of the high -fre-quency components of the picture signal whenthe scanning spot covers several mosaic glo-bules in a TV camera tube simultaneously.

aperture lens. In electron optics a hole in a plateelectrode separating two electric fields. Elec-trons passing through the hole are deflected toproduce focusing.

A power supply. Any device that provides fila-ment power used for heating the cathode ofa vacuum tube.

apparent power. In an alternating current circuit,the voltage in volts multiplied by the currentin amperes, without consideration of phaserelations. The apparent power is therefore notthe true power if the circuit contains anyreactance.

Applegate diagram. A diagram consisting of anumber of lines whose slopes are proportionalto electron velocities, and which indicateswhere the electrons will bunch in a velocity -modulated tube.

aquadag. A suspension of graphite particles inwater, used to deposit a carbon coating on theglass envelopes of vacuum tubes and cathoderay tubes for any of several purposes, such asshielding the electrodes from light, absorbingheat, or collecting stray electrons. By exten-sion, the coating itself.

arc. The flow of electric current through air,gas, or vapor.

arc -back. A breakdown of mercury vapor in mer-cury-vapor rectifiers permitting conduction inthe opposite direction to normal.

arc 'converter. An rf oscillator utilizing an elec-tric arc and a tank circuit to generate a pul-sating or alternating current.

argon. A gas used in some rectifier tubes andelectric lamps. It gives off a purple glow whenionized.

arm. The part or parts of a filter or attenuatorthat are connected in series with the circuit.Also called the series element.

armature. The part of a motor or generator thatincludes the main current -carrying winding. Indc machines the armature is the rotating part,but in ac machines it may either rotate or bestationary. Also, the pivoted or spring -mountediron portion of a magnetic loudspeaker, vi-brator, buzzer, relay, or magnetic phonopickup.

armature reaction. The reaction between arma-ture flux and field flux causing a redistributionof flux lines in a dynamoelectric motor orgenerator.

array. See antenna array.

arrester. See lightning arrester.

artificial antenna, A device having all the essential

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characteristics of an antenna except that itconverts the transmitter output power intoheat instead of radio waves. Used chiefly fortesting and adjusting transmitters. Also calleddummy antenna,.

artificial line. A filter circuit having character-istics similar to those of a transmission line ofgiven length.

artificial load. A dissipative device having theimpedance characteristics of an antenna, atransmission line, or some other practical util-ization circuit, which it replaces for test or ad-justment purposes.

asbestos. A non -inflammable mineral of fibroustexture, available in flake or pressed form, usedfor heat -insulating and fire -proofing.

aspect ratio. The ratio of the width of a tele-vision image to its height, currently standard-ized at 4 to 3.

astafic. Without polarity.astigmatism. A defect of a lens or other optical

system in which rays coming from one point ofan object are not all brought to the desiredfocal point.

A supply. Filament voltage supply of a vacuumtube circuit such as an A battery or a filamentwinding on a power transformer.

asynchronous. Not synchronous.AT -cut crystal. A crystal cut at a 35° angle to

the Z axis. It has low temperature drift.atmosphere. A complex mixture of gases, prin-

cipally oxygen and nitrogen, surrounding theearth for a distance of nearly 100 miles, andexerting a pressure of 15 pounds per squareInch at the surface of the earth, which valueis a unit of pressure called one atmosphere.

atmospheric duct. See duct.

atmospheric interference. Crackling and hissingnoises caused in the receiver by electrical dis-turbances in the atmosphere. These disturb-ances radiate electromagnetic waves that arepicked up by antenna systems. Also called at-mospheric disturbance, atmospheric noise, at-mospherics, static, or QRM, and particularlynoticeable during thunderstorms.

atom. The smallest particle into which mattermay be divided by chemical means. An atomhas a nucleus consisting of electrons, protons,neutrons, etc.. with additional electrons re-volving around the nucleus. Each of the knownelements has a different number and arrange-ment of electrons and protons in its atoms.

atomic weight. The weight of any atom as com-pared to the weight of the oxygen atom, whichis set at 16.

attenuation. The decrease in the strength of aradio wave as it travels away from the trans-mitter. Also any decrease in the strength ofa signal or electrical impulse.

attenuation equalizer. A network of resistors,coils, and condensers designed to change thecurrent amplitude in the circuit so that itvaries in a desired way with frequency, with-out regard to phase.

attenuator. A device, usually an arrangement ofvariable resistances, that reduces the strengthof a signal a desired amount without appre-ciable distortion.

audibility. The strength of a sound or signal ascompared to the strength required to producea sound that can just barely be heard.

audible. Capable of being heard. The range ofhuman hearing is usually within the limits of20 and 20,000 cycles per second, but variesgreatly in different persons.

audio. Pertaining to currents or frequenciescorresponding to normally audible soundwaves.

audio amplifier. A vacuum tube stage that in-creases the voltage or power or both of anaudio -frequency signal.

audio frequency (af). A frequency correspondingto an audible sound wave. The extreme limitsof audio frequencies vary with the individual,normally from about 20 to 20,000 cycles persecond.

audio frequency meter. An instrument for meas-uring audio frequencies.

audio -frequency peak limiter. A circuit used in anaudio -frequency system to cut off peaks thatexceed a predetermined value.

audio -frequency transformer. An iron -core trans-former used for coupling audio -amplifier cir-cuits.

audiometer. An instrument for measuring theloudness of sounds.

audion. The three -electrode vacuum tube in-vented by De Forest.

audio oscillator. An oscillator that generatesaudio -frequency voltages.

audio signal. The electrical equivalent of sound.audio transformer. Audio -frequency transformer.aural. Pertaining to hearing.aural -null direction finder. A direction finder re-

ceiver in which a loop antenna is rotateduntil minimum sound is heard in the head-phone; bearings are read from a compass scaleassociated with the loop antenna control.

aural transmitter. The radio equipment used forthe transmission of the aural (sound) signalsfrom a television broadcast station.

auto alarm. An automatic device for maintain-ing a continuous watch for distress signals,consisting of a receiver tuned to the interna-tional distress frequency, and a selector thatwill respond only to the international autoalarm signal.

autodyne reception. A system of heterodyne re-ception in which one tube acts both as an os-cillator and a detector.

Auto-Expressionator. The volume -expander cir-cuit used in some Crosley receivers.

automatic. Self-acting.automatic bass compensation (abc). A resistor

and condenser circuit used in some receivers tomake low audio -frequency notes sound morenormal at low volume -control settings. The cir-cuit automatically compensates for the poorresponse of the human ear to weak low -fre-quency sounds.

automatic brightness control. A circuit that auto-matically keeps the average brightness of thereproduced image constant in a television re-ceiver.

automatic circuit -breaker. A device that auto-matically opens a circuit when the currentbecomes excessive.

automatic contrast control. A circuit that variesthe bias on one or more tubes so that the con -

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trast of the television picture is maintainedat a constant average level.

automatic direction finder (adf). Electronic deviceusually for marine or aviation use, that pro-vides a bearing to any transmitter whose loca-tion is known.

automatic frequency control (afc). A circuit thatkeeps a superheterodyne receiver tuned accu-rately to a desired station.

automatic gain control (age). A circuit that auto-matically maintains the output of a sound orTV receiver relatively constant despite varia-tions in carrier signal amplitude. An auto-matic volume control.

automatic grid bias. Use of the voltage dropacross a resistor in the grid or cathode circuitof a tube as the C bias voltage for the gridof the tube, eliminating the need for a sepa-rate C bias voltage source.

Cu. toil MulmulaAutomatic Record Changer

automatic record changer. An electric device thatautomatically plays a number of phonographrecords one after another.

automatic regulator. A device for regulating asystem so that changes in its functioning arecarried out electrically or mechanically ratherthan manually.

automatic tuning. An electrical, electro-mechani-cal, or mechanical system that tunes a receiverautomatically to a predetermined station whena button or lever is pushed.

automatic volume control (avc). An automaticgain control in a sound receiver.

automatic volume expansion Cave). A special audiocircuit that increases the volume range of aradio program or phonograph record by mak-ing the weak passages weaker and loud pas-sages louder.

automobile receiver. A receiver designed for in-stallation in an automobile, usually underneaththe dashboard. Filament voltages are obtaineddirectly from the 6 -volt automobile storagebattery, and the required higher de voltagesare usually obtained from a vibrator powerpack in the receiver. Also called auto radio.

auto radio. An automobile receiver.

Autosyn motor. See Selsyn motor.

auto -transformer. A transformer having one con-tinuous winding. All of the winding serves asthe secondary, and a part of the windingserves also as the primary, or vice versa.

average. The average of a number of quantitiesis obtained by dividing the sum of the quanti-

ties by the number of quantities involved.average brightness. The average illumination in

the television picture.average power output. The radio -frequency power

delivered to the output terminals of an ampli-tude -modulated transmitter averaged over amodulation cycle.

aviation channels. Frequency bands assigned forradio communication between aircraft andground stations. They are both above and be-low broadcast -band frequencies.

Bback electromotive force (back emf). A voltage de-

veloped in an inductive circuit by a changingor alternating current, whose polarity is suchthat it opposes the change in current that pro-duces it. Also called counter electromotiveforce.

background. The average illumination of a tele-vision scene, contained in the de component ofthe video signal.

background control. See brightness control.background noise. Noise heard along with a re-

ceived program, due to atmospheric interfer-ence or to circuit noises.

background voltage. In a radio direction finder,any voltage induced in the loop other thanthe desired signal voltage.

back -lash. Movement or play in the gears or partsof a tuning mechanism or other system, allow-ing one gear to be moved a certain amountwithout moving connected gears or parts.

backlight. Illumination applied to the rear of theiconoscope in a film pickup to provide a mini-mum light level and thus assist in controllingshading.

back porch. The portion of the blanking pedestaloccurring after the horizontal synchronizingpulse.

back -shunt signalling. A signalling system inwhich energy is delivered to the antenna whena telegraph key is closed and to a "back shunt"non -radiating circuit when the key is open.

back -wave. A signal heard from a telegraphtransmitter with the key open because of im-proper neutralization of the transmitter ampli-fier.

baffle. A wood, metal, or composition horn, fiatsurface, or box used with a loudspeaker to in-crease the effective length of the air path fromthe front to the back of the diaphragm, there-by reducing interaction between sound wavesproduced simultaneously by front and backsurfaces of the diaphragm and improving thefidelity of reproduction. Also, a disc with ahole in it, used in an electfon gun to restrictelectrons travelling at such an angle that theycan't be focused into the beam.

Bakelite. A phenolic compound having high elec-trical resistance, used as an insulating ma-terial.

balanced aramature unit. The driver unit used insome magnetic loudspeakers. It has a smallmoving iron armature surrounded by windingscarrying audio currents and pivoted betweenthe poles of a permanent magnet. Variationsin the audio current cause correspondingchanges in magnetism, making the armaturerock back and forth. A diaphragm coupled tothe armature produces sound waves.

7

balanced circuit. A vacuum -tube circuit in whichthe tube capacity is balanced or compensatedfor by an external capacity. Also, any circuitthat is adjusted so that two factors balanceeach other.

balanced modulation. A system of adding sound toradio -wave transmission whereby only thesidebands are transmitted, the carrier beingeliminated.

balancer. The portion of a radio -direction finderused to eliminate the antenna effect due toloop -ground capacity.

balancing condenser. A condenser used as part ofa balanced circuit. Also, the condenser thatmakes both sides of a direction -finding loopequal in capacity to ground when the antennaIs set for minimum signal pickup.

ballast resistor. A resistor that has the character-istic of greatly decreasing its resistance whencurrent flow decreases, and increasing its re-sistance when current increases, thereby main-taining essentially constant current over a con-siderable range of voltage variation.

ballast tube. A ballast resistor mounted in anevacuated glass or metal envelope to improvethe automatic voltage regulating action by re-ducing the radiation of heat from the resistorelement. Also, a line -dropping resistor housedin a tube envelope.

ballistic galvanometer. An instrument for measur-ing a momentary discharge or pulse of energy.It is a microammeter having a coil with a highmoment of inertia and no retarding spring,so that when energized, the indicator is freeto rotate until stopped by friction. The totalmovement of the pointer until it comes to restis proportional to the energy being measured.

band. A group of frequencies within two definitelimits and used for a specified purpose.example. the standard broadcast band extendsfrom 550 kc to 1600 kc.

band -elimination filter. Two or more tuned circuitsarranged to attenuate a band of frequenciesbetween predetermined upper and lower fre-quency limits.

band-pass filter. Two or more tuned circuits ar-ranged to pass a certain band of frequencieswhile attenuating or rejecting higher and lowerfrequencies.

band selector. A band switch that permits selec-tion of any one of the bands in which a re-ceiver or transmitter is designed to operate.

bandspread tuning. Tuning by means of a gang oflow capacity condensers connected in parallelwith the main tuning gang. After tuning tothe desired band with the main gang, it ispossible to "spread" that band over the band -spread dial because the small capacities givea smaller frequency change per degree of rota-tion. Also, a mechanical system for achievingthe same result by using a vernier tuning knobhaving a high drive ratio, so that many turnsof it are needed to move the main condensergang appreciably.

band switch. A switch that simultaneouslychanges all tuning circuits of a radio receiveror transmitter to a desired band of frequencies.

band width. The difference in cycles per secondbetween those two frequencies at which theresponse is a specified amount of the peakresponse.

bank winding. A method of winding coils in whichsuccessive turns are placed in two or morelayers so that a multi -layer coil is wound with-out going back to the starting point. This

procedure reduces the distributed capacity ofthe coil.

bantam tube. A compactly designed tube havinga standard octal base but a considerablysmaller glass envelope than a standard glasstube; designated by the letters GT followingthe tube type number.

bor. A term formerly used to mean a soundpressure of one dyne per square centimeter,but now avoided because in all fields exceptacoustics the bar is equal to 1,000,000 dynes persquare centimeter.

bar generator. A generator for producing pulsesequally separated in time that are synchron-ized so they produce a stationary bar patternon a television screen for test purposes.

barium. A chemical element used In photoelectriccells.

Barkhausen-Kurz oscillator. An oscillator of the re-tarding field type in which the frequency ofoscillation depends upon the electron transittime within the tube.

bar magnet. A magnetized straight bar of steelserving as a permanent magnet.

barometer. An instrument for measuring thepressure of the atmosphere, used chiefly forweather forecasting.

bar pattern. A pattern of repeating lines or barson a television screen. The spacing betweenthe bars is used to determine the degree oflinearity of the horizontal or vertical scanningsystems.

base. The number upon which a system of loga-rithms is constructed. The base of the com-mon system of logarithms is 10. Example :loglo 10,000 = 4, which means that 10' =10,000; login 351 = 2.545, which means that10' 646 = 351. Loge 953 = 6.116, which meansthat e 9 116 = 453. The base is designated tothe right of and below the abbreviation "log";when no base is specified in ordinary problemsof computation, the base 10 is always assumed.

basket winding. A criss-cross coil winding Inwhich each turn is so placed that adjacentturns .are separated by a considerable spaceexcept at the points of crossing, reducing thedistributed capacity of the coil.

bass. Low audio frequencies, generally consid-ered to be those frequencies below 300 cyclesper second.

bass -boost circuit. A circuit designed to emphasizelow audio frequencies.

bass compensation. Any means for offsetting thenatural drop in the response of the human earto low audio frequencies at low volume levels.

bass control. A manually adjusted control pro-vided on a receiver for the purpose of empha-sizing low audio frequencies.

bass response. The ability of a loudspeaker oramplifier to handle low audio notes, or thesensitivity of the human ear to low audio notes.

bathtub condenser. A capacitor enclosed in ametal can with rounded corners resembling abathtub.

battery. One or more dry cells or storage cellsconnected together to serve as a de voltagesource.

battery receiver. A receiver using batteries as asource of power.

baud. The unit of telegraph signalling speed, in8

terms of the duration of the shortest signalingpulse. A telegraphic speed of one baud is onepulse per second.

bay. One complete section of a number of am-plifiers or other transmitter units mounted onracks. Also a section of a complex antennaarray.

bayonet base. A type of tube and lamp base hav-ing two projecting pins on opposite sides thatengage in corresponding slots in the bayonet -shell socket. Electrical contact is made bymeans of pins or rings on the bottom of thebase.

Bazooka

bazooka. A quarter -wave shield used at the endof a coaxial transmission line to raise the im-pedance of the outer conductor to permit con-necting to a balanced transmission line. A linebalance converter.

B battery. A battery having many small cellsconnected in series, used for supplying devoltages to the plate and screen -grid electrodesof radio tubes used in battery -operated equip-ment.

beacon. See radio beacon.

beacon course. The equisignal zone or beam of anaircraft radio beacon, designating a coursethrough the sky.

beam. The stream of electrons passing from thecathode to the fluorescent screen of a cathode-ray tube. Also a constant radio signal trans-mitted for guidance of aircraft. Also, radiatedenergy that is concentrated and directed in aparticular path.

beam angle. The angle enclosing a greater partof the energy transmitted from a directionalantenna.

beam antenna. An antenna whose radiation or re-ception is practically confined to a narrow beamextending in a definite direction.

Beam -a -Scope. Trade name for a built-in shieldedloop antenna used in some General Electricreceivers.

beam bender. See ion trap.

beam, convergent. A beam of light whose raysmeet (converge) at a single point.

beam current. The current in the stream of elec-trons in a cathode-ray tube.

beam, divergent. A beam whose rays spread out.

beam of light. A group or pencil of light rays.

beam, parallel. A beam of light whose rays areexactly parallel to one another.

beam power tube. A vacuum tube designed for usein the output stage of a radio receiver. De-flecting electrodes in the tube concentrate theelectrons into beams which force secondaryemission electrons back to the plate.

beam relaxer. A TV sweep oscillator that gener-ates the current wave required for magneticdeflection of such amplitude that subsequentamplification is not needed.

bearing. A term used in navigation to designatethe direction of one point with respect to an-other or to the points of a compass.

beat. A regularly recurring pulsation resultingfrom the combination of two or more tones orelectric waves of different frequencies.

beat frequency. The frequency obtained whensignals of two different frequencies are com-bined and rectified. The beat frequency is equalin numerical value to the difference betweenthe original frequencies.

beat frequency oscillator (bfo). An audio -fre-quency oscillator whose output is obtained bycombining and rectifying two known higher -frequency signals generated by or obtainedfrom separate circuits. Also, an oscillator usedto provide a beat signal when its output ismixed with an incoming cw signal, so that anaudible output can be obtained.

beat -frequency receiver. Early name for a super-heterodyne receiver.

beating. Combining of two different frequenciesto produce a new signal having pulsations inamplitude at the difference or beat -frequencyvalue.

beat note. An audible frequency produced by thebeating of two higher frequencies.

bel. The unit for logarithmic expression of ratiosof power, voltage, or current, named afterAlexander Graham Bell, inventor of the tele-phone. The number of bels is the commonlogarithm of the power ratio. In radio work, asmaller unit called the decibel is used insteadof the bel; a decibel is one -tenth of a bel.

B eliminator. A power pack that converts ac powerline voltage to the pure de voltages requiredby plate and screen -grid circuits of radio tubesthereby eliminating the need for B batteries.

Bellini-Tosi direction finder. An early radio com-pass.

bell wire. A common name for the cotton -coveredNo. 18 copper wire used for making doorbelland thermostat connections in homes.

beta rays. Rays consisting of negatively chargedparticles or electrons. Cathode rays.

Beverage antenna. A directional antenna of lowheight, having a length that is some multipleof the received wavelength.

B -H curve. A curve showing the relationship be-tween magnetic flux density, (B) produced ina magnetic path and the magnetic force perunit length (H) in that path.

bias. The fixed dc voltage applied between thecontrol grid and cathode electrodes of a radiotube. Also called C bias.

bias cell. A tiny 1 -volt or 1% -volt cell used singly

9

or in series combinations to provide a negativeC bias voltage for a vacuum tube amplifier cir-cuit.

bias resistor. The cathode resistor that providesa C -bias voltage for a tube.

bidirectional. In two directions, one opposite theother. An ordinary loop antenna is bidirec-tional, picking up energy from two oppositedirections.

bidirectional pulses. Pulses, some of which risein one direction and the remainder in theopposite direction.

bilateral. Having two sides.bilateral antenna. An antenna that radiates or re-

ceives radio waves best in two direction 180°apart.

bilateral network. A network in which a givencurrent flow in either direction causes the samepotential drop.

billboard array. An antenna array consisting ofstacked dipoles % to % wavelength apart witha large sheet -metal or screen reflector behindthe dipoles.

bimorph cell. A cell consisting of two crystal ele-ments cemented together, used in crystal head-phones, microphones, pickups, and loudspeak-ers.

binaural. Having two ears, or the effect of hear-ing with both ears. Also, pertaining to soundtransmitted over two different paths, creatingthe sensation of sound position.

binaural effect. The effect of sound on both ears.The difference in the two sound -path lengthsmakes it possible for a person to determine thedirection from which a sound is coming.

binder. A resinous material that causes thevarious materials of a phonograph record com-pound to adhere to one another. Also, thecement -like material used for a similar pur-pose in carbon resistors and powdered -ironcores.

binding post. A terminal to which wires may beattached by screws or clamps for making quickelectrical connections.

bipolar. Possessing two poles.

birdie. A high-pitched whistle. It is a beat notehaving a high audio frequency.

blacker -than -black region. That portion of thevideo signal above the black level. It containsthe synchronizing pulses.

black level. In television, the voltage represent-ing the color black. Usually it is not greaterthan 80% of the maximum television signalamplitude.

blanking. The process of applying negative volt-age to the control grid of the cathode-ray tubeto cut off the electron beam during the retraceor flyback period.

blanking pedestal. See blanking pulse.blanking pulse. The signal introduced into the

complex video signal at or above the blacklevel, used to blank out video signals duringthe transmission of synchronizing signals.

blasting. A distortion of sound caused by over-loading a microphone, loudspeaker, or someother part.

bleeder current. A current drawn continuouslyfrom a power -pack or other voltage source to

improve voltage regulation or to increase thevoltage drop across a resistor.

bleeder resistor. A resistor used to draw a fixedbleeder current from a power pack.

blister. Housing for radar antenna. A Radome.block diagram. Simplified plan of an electronic

system in which the several stages or sectionsare shown as rectangles.

blocked -grid keying. Method of keying a telegraphtransmitter by applying sufficient bias to blocktubes when the key is open. Closing the keyremoves the bias, allowing plate current toflow.

blocked resistance. That part of the resistance ina loudspeaker due to electrical losses. It canbe measured only when the moving elementsin a loudspeaker have been blocked so theycannot move.

blocking. Stopping of operation, as by applyinga high negative bias to the grid of a tube tocut off plate current.

blocking condenser. A condenser used in a radiocircuit to prevent the flow of direct currentwhile allowing ac signal currents to pass.

blocking oscillator. A vacuum -tube oscillator op-erating intermittently, with grid bias increas-ing during oscillation to a point where it stopsthe oscillation, then decreasing to a point atwhich oscillation can be resumed.

blooming. Increase in spot size in a cro tube re-sulting from abnormal brilliancy. Also increasein picture size due to oversweeping because ofreduced high voltage.

blooper. Slang term applied to a regenerativereceiver which radiates a signal when improp-erly operated.

blow-out magnet. A permanent magnet or electro-magnet used to extinguish an electric arc inan arc transmitter or on heavy-duty switchesor relays by forcing the ionized gases out ofthe gap.

bobbin. A coil of wire wound on a form, or theform itself.

body. A mass or portion of matter separate fromother masses.

body capacity. The capacity existing between thehuman body and a piece of radio apparatus.

bombardment. The striking of electrodes or otherparts by ions or electrons.

bonding. Connecting metal objects together withheavy wire or metal straps so they will be atthe same potential (usually ground potential).

book condenser. A two -plate condenser hingedlike the pages of a book. Capacity variation isobtained by changing the angle between theplates.

boom. An adjustable mechanical arm for holdinga camera or microphone in a number of differ-ent positions.

boom shot. A picture taken by a camera mountedon a boom. Loosely, any shot for which thecamera is high.

booster. A pre -amplifier connected between theantenna and receiver to increase the signalstrength at the receiver input.

bootstrap circuit. A circuit arranged so that thepotential at some point is "lifted" to a higherpoterttio with .respect to ground by a feed -

10

back arrangement, in addition to the potentialchanges caused by the signal.

bounce. Rapid arid irregular changes in bright-ness of a TV picture. Also, irregular up anddown movements of the picture.

B power supply. Any power -supply device con-nected in the plate circuit of a vacuum tube.

breadboard construction. Layout of radio partsand wiring so parts may be easily changedor moved during experimental work. Origi-nally on a wooden board but now usually on ametal chassis.

breakdown voltage. The voltage at which the in-sulation between two conductors will becomeconductive.

break-in keying. A method of operating a radiotelegraph communication system in which thereceiver at the transmitter location is capableof receiving signals during transmission spac-ing intervals.

break-in operation. A type of radio communica-tion in which the receiving operator can inter-rupt the transmitting operator at any time.

bridge circuit. A circuit consisting of four re-sistances or impedances connected in series toform a square, with a voltage source con-nected between one pair of opposite junctionsand an indicator (usually a galvanometer) be-tween the other pair. The bridge is said to bebalanced when it is adjusted so no currentflows through the indicating meter.

bridged -T network. A T -connected network witha fourth branch connected across the twoseries arms of the T, between an input ter-minal and on an output terminal.

bridge rectifier. A four -element rectifier circuitconnected in the characteristic four -corneredarrangement of a bridge circuit. AC voltageis applied to one pair of opposite junctions orcorners, and de voltage is obtained from theother pair.

bridging amplifier. An amplifier requiring neg-ligible input power that can be connectedacross another circuit without disturbing thatcircuit's normal function.

bright level. The voltage representing white, thebrightest part of a TV image, usually set atabout 15% of the maximum TV signal ampli-tude.

brightness. The background intensity of a tele-vision picture. Also, the measure of theamount of light flux radiated by an object,usually measured in foot -lamberts.

brightness control. In a television receiver, thecontrol that varies the average illumination ofthe reproduced image.

brilliance. Degree of reproduction of the higheraudio frequencies. Also, the brightness of aTV picture.

brilliancy control. Same as brightness control.British thermal unit (btu). An English unit of

measure of heat quantity. It is the heat re-quired to raise the temperature of one poundof water at its maximum density, 1° F.

broadband amplifier. An amplifier having flat re-sponse over a wide range of frequencies.

broadcast. A radio transmission intended for re-ception by the general public.

broadcast band. The group of frequencies as-signed to broadcast stations. In the U. S., thestandard AM broadcast band is from 550 kc to

1600 kc; the FM broadcast band is from 88 to108 mc; in between are several short-wavebroadcast bands.

broadcast interference. Interference produced byany transmitter with any broadcast reception.Specifically, interference of amateur radiotransmitters with reception on standardbroadcast receivers.

broadcast station. A radio station used for trans-mitting programs to the general public.

broadside directional antenna. An antenna arraywhose radiation is substantially at rightangles to the line along which its elementsare arrayed.

broad tuning. A characteristic of a receiverwherein the pass band of the tuning circuitsis wide.

bronze. An alloy of copper and tin.

Brown and Sharpe Gauge. See American WireGauge.

brush. A metal or carbon block used to makecontact with a moving part in an electricalcircuit.

brush discharge. Visible ionization occurring atsharp points, corners, or bends of conductorscharged to high potentials. Corona discharge.

brute -force filter. A low-pass filter depending onlarge values of capacity and inductance ratherthan on resonant effects to block ac com-ponents while passing direct current.

B supply. Plate -voltage supply of a vacuum -tubecircuit.

buck. To oppose.

bucking coil. A coil whose magnetic field opposesthe magnetic field of another coil.

buffer. Any part or circuit used to reduce unde-sirable interaction between radio circuits.

buffer amplifier. An isolating amplifier in whichthe reaction of output load impedance vari-ation on the input circuit is reduced to aminimum.

buffer condenser. A condenser used to reduce volt-age surges that might affect following parts.

bug. A semi -automatic code transmitting key inwhich movement of a lever to one side pro-duces a dot or a series of dots of equal dura-tion and spacing, and movement to the otherside produces a single dash. Also, a slang ex-pression for a defect or trouble.

built-in aerial. An aerial that is an integral part ofa receiver. A loop aerial, a power -line connec-

Built-in Aerial

11

tion, metal ribbons, or some other pickup de-vice mounted in the receiver cabinet.

buncher grids. The elements in a velocity-modu-.lated tube, such as a Klystron, whose poten-tials vary the electron velocities so thatbunches of electrons are formed in the driftspace.

bunching of electrons. Application of rapidlyalternating fields to a uniform beam of elec-trons so that their velocities will be modu-lated. After a proper interval of travel, thefaster electrons overtake preceding slowerones and bunches are formed that can be usedto deliver energy to a resonant cavitY.

bus bars. The heavy copper bars used on switch-boards to carry current. Also, an uninsulatedcopper wire of about 12 or 14 gauge.

bushing. A tube or washer used for lining or in-sulating a hole in a chassis, or as a bearing.

butterfly condenser. A variable capacitor whosemovable plates resemble the shape of a butter-fly.

butterfly tank. A vhf resonant circuit using themechanism of a butterfly condenser in such away that the rotor varies both the inductanceand the capacity, thus giving a wide tuningrange.

buzz. A rasping sound ranging in frequency be-tween a hum and a squeal. For example, anaudible disturbance in the sound output of atelevision receiver due to synchronizingsignals that get through the sound channel.

BX cable. Flexible metal conduit used to protectpower line wiring in buildings and in high -power radio apparatus.

by-pass condenser. A condenser used to provide alow -impedance path around a part or circuit.

Ccabinet. The wood, metal, or plastic housing in

which electronic equipment is placed.cable. A bundle of two or more wires held to-

gether, as by lacing, shielding, or an insulat-ing sleeving. Also a term applied to largersizes of wire, used singly or in combination,usually heavily insulated, and often lead -covered.

cadmium. A metal sometimes plated on a steelchassis to improve its appearance and preventrusting.

caesium. An alkali metal used in some photo-electric cells.

cage antenna. An antenna whose conductors aregroups of parallel wires in a cylindrical ar-rangement.

calibrate. To determine by measurement or com-parison the true values for each scale divisionof a meter or other instrument. To determineand record the settings of a control that cor-respond to particular values of frequency,voltage, current, or some other characteristic.

call letters. Government -assigned Identifying let-ters for a radio or TV station.

calorie. The unit of heat energy in the metricsystem. One calorie is the amount of heatenergy required to raise the temperature ofone gram of water one degree Centigrade.There are 252 calories in a British thermalunit (btu).

calorimetric wattmeter. An instrument for micro-

wave power measurements in which the rfenergy is changed to heat and the amount ofheat is measured.

cam. A rotating or sliding part used to convertrotary motion to linear motion, or vice versa,or to transfer motion from one direction toanother.

cambric, varnished. A fine white linen or cottonfabric, varnish -impregnated and baked, andused as an insulating material in coils andother parts. When in the form of tubing, it iscalled spaghetti.

Camera

camera. The part of a television transmitting ap-paratus in which the image of the scene to betelevised is converted into equivalent electricalimpulses.

camera chain. The group of amplifiers, monitors,and the sync generator associated with a TVcamera; all the signal equipment between thecamera and the transmitter.

camera preamplifier. A video amplifier, mountedin or very near the camera, for providingenough amplification to offset losses in thecable leading to the control room.

camera tube. The cathode-ray tube used at thetelevision transmitter to change the lightvariations of the scene into an equivalentelectrical signal.

candlepower (cp). Unit of measure of light in-tensity.

Candohm. A wire -wound resistor, usually tap-ped, wrapped in heavy fiber insulating paperand then encased in metal. Used for bleederresistors and voltage divider applications.

capacitance. Capacity.

capacitive coupling. Coupling in which a con-denser provides a path for signal energy be-tween two circuits.

capacitive reactance. The reactance in ohms acondenser offers to ac. It decreases as eitherfrequency or capacity or both are increased.

capacitor. A condenser.

capacitor split -phase motor. An induction motorusing a series condenser to produce the rotat-ing magnetic field required to bring an induc-tion motor up to synchronous speed whenoperated from a single-phase ac source.

capacity (C). The ratio of the charge stored in acondenser to the voltage producing the charge.The unit of capacity is the farad; a capacityof 1 farad exists when a change of 1 volt persecond produces a current of 1 ampere. In

12

radio work, capacity is measured in micro -farads (mfd) and micromicrofarads (mmf); 1mfd is equal to 1,000,000 mmf.

capacity bridge. A bridge for precise measure-ments of capacity.

carbon. An element used in the construction ofradio parts such as resistors, dry cells, andmicrophones.

carbon granules. Small particles of carbon usedin microphone buttons.

carbonized. Pertaining to an insulator that hasbeen converted to a partial conductor by beingburned by an arc, so that the residue of carbonacts as a conducting medium.

carbon microphone. A microphone in which thediaphragm applies a varying pressure to acontainer filled with carbon granules, therebycausing the resistance of the microphone tovary in accordance with the varying pressureof sound waves on the diaphragm.

St, iaca

Courtesy Westei n Electric Co.

Carbon Microphone

carbon -pressure recording. Electromechanical fac-simile recording in which a pressure deviceacts upon carbon paper to register upon therecord sheet.

carbon resistor. A resistor made of carbon par-ticles and a ceramic binder usually molded in-to a cylindrical shape, with leads attached toopposite ends.

cardioid pattern. A heart -shaped pattern repre-senting the response or radiation character-istics of certain antennas or the response char-acteristics of certain microphones.

carriage. The overhead feed mechanism of discsound -recording equipment that carries thecutting head.

carrier. A current, voltage, or wave having thefrequency assigned a radio or TV station.

carrier current. The alternating current associat-ed with a carrier. Also, the rf carrier currentsent over power lines for communication pur-poses.

carrier frequency. The frequency of the originalunmodulated wave produced by a transmitter.

carrier -frequency stability. A measure of the abil-ity of a transmitter to maintain an assignedfrequency.

carrier level. The strength of a carrier, expressedas power or voltage, usually applied to anunmodulated carrier.

carrier noise level. The noise level produced by

undesired variations of a radio -frequencysignal in the absence of any intended modula-tion.

carrier -operated noise suppression (CONS). A sys-tem in which the receiver is silenced (toeliminate noise) until the carrier exceeds acertain strength, set to be sufficient to overridethe noise. Used in communications systems inwhich the transmitter carrier is turned off andon frequently.

carrier suppression. A method of transmission inwhich the carrier wave is not transmitted.

carrier wave. The unmodulated component of asignal wave, usually called simply the carrier.It carries the sound, picture, code, or fac-simile signals from the transmitting stationthrough space to receivers.

carrying capacity. The maximum current strengtha conductor can safely transmit without over-heating.

cartridge fuse. A fuse enclosed in a cartridge inthe shape of a rod or cylinder, with contactsat the ends.

cascade. In series, such as tuning circuits or, am-plifier stages used one after another.

cascade limiter. An FM limiter system using twoor more limiter tubes in series, or cascade,to improve operation for both weak and strongsignals.

catcher grids. The elements in a velocity -modu-lated tube, such as the Klystron, used to ex-tract the energy contained in the bunchedelectrons.

cathode. The electron -emitting electrode ofradio tube.

cathode current. The total current passing fromthe cathode through space to the other elec-trodes in a vacuum tube.

cathode follower. A circuit in which the outputis taken between cathode and ground, provid-ing high -impedance input with low -impedanceoutput.

cathode -heating time. The time in seconds re-quired for the cathode of a tube to reach nor-mal operatjng temperature after normal voltage is applied to the heater.

cathode keying. Method of telegraphic transmis-sion in which the key is connected in the platereturn lead to the cathode or filament centertap.

cathode modulation. Amplitude modulation inwhich the modulation is applied between thecathode and ground, thus varying the gridbias and plate voltage simultaneously.

cathode ray. A ray or beam of electrons emittedfrom a cathode.

cathode-ray oscilloscope. A test instrument usinga cathode-ray tube to make visible the waveform of a varying current or voltage.

cathode-ray picture tube. The cathode-ray tubeused in television receivers to reproduce thescenes being transmitted.

cathode-ray tube. Any vacuum tube in which abeam of electrons is directed at a fluorescentscreen by an electron gun, producing a glowon the screen at the point of impact. The beampasses between electrostatic deflecting platesor electromagnetic deflecting coils that bendit enough to produce any desired pattern orpicture on the screen when the proper vary-ing voltages are applied to the deflecting sys-tem.

13

cathode-ray tube screen. The fluorescent materialcovering the inside surface of the picture endof a cathode-ray tube.

cathode spot. Heated area of the mercury surfacein mercury pool rectifiers, serving as a sourceof electrons.

cathode sputtering. A process used in the produc-tion of the metal master of a phonograph rec-ord, wherein the wax or lacquer original iscoated with a conducting layer by means ofan electrical discharge in a vacuum.

cation. A positive ion.

catwhisker. A small, sharply pointed wire usedin a crystal detector to make contact with asensitive point on the surface of the crystal.

cavity gap impedance. The impedance of a cavityresonator across the gap.

cavity resonance. The characteristic of a cavity,determined by its dimensions, that causes itto have maximum response at a particularfrequency.

cavity resonator. A space normally bounded by anelectrically conducting surface in which os-cillating electromagnetic energy is stored, theresonant frequency of which is determined bythe size and shape of the enclosure.

C battery. The battery used for supplying anegative C bias voltage to the control grid of avacuum tube.

C bias. An applied voltage used to make the con-trol grid of a vacuum tube negative with re-spect to the cathode.

C bias detector. A vacuum tube operated with al-most enough negative bias to cut off plate cur-rent. The tube operates on the lower bend ofthe characteristic curve, and detection takesplace in the plate circuit.

celestial navigation. Calculation of position bythe use of heavenly bodies.

cell. A single unit capable of serving as a devoltage source. A primary cell, such as a drycell, cannot be recharged when exhausted. Asecondary cell, such as the cell of a storage bat-tery, can be recharged by passing a currentthrough it in the reverse direction. The termcell is also used to designate light-sensitivetubes (photoelectric cells and selenium cells).

Celotex. A fiber wallboard used in loudspeakerbaffles because of its sound -absorbing qualities.Also used in radio and sound picture studiosto control the amount of reverberation.

center frequency. In frequency modulation, thefrequency of the unmodulated carrier. Withmodulation, the instantaneous frequencyswings above and below the center frequency.In general, the average frequency of theemitted wave when modulated by a symmetri-cal signal.

centering. Shifting the trace on an oscilloscopeor the image on a television tube so that it iscentered on the screen.

centering control. An adjuster for shifting theimage on the screen of a cathode-ray tube byvarying either the de potential 'applied to de-flection plates, by varying the de currentthrough or the position of deflection coils, orby varying the position of permanent magnets.The vertical centering control moves the imageup or down, and the horizontal centering con-trol moves it to either side.

center of curvature. The point equidistant fromall points on the surface of a spherical mirror.

If the mirror is considered to be a segment ofa complete sphere, the center of curvaturewould be the center of the sphere.

center -tap keying. Keying a telegraph transmitterstage by interrupting the current flowing tothe filament center -tap connection through theplate return lead.

coin. A prefix denoting "a, hundredth of."

centigrade (C). The metric scale of temperature,in which 0 is the freezing point and 100 is theboiling point of water at sea level.

centimeter (cm). In the metric system of meas-urements, a unit equal to one hundredth of ameter, or approximately .39 inch. There are2.54 centimeters in one inch.

ceramic. A clay -like material, consisting mainlyof aluminum and magnesium oxides, whichafter molding and firing is used as insulation.Glazed ceramic is porcelain.

ceramic capacitor. A capacitor whose dielectric isceramic.

chain. A network of stations connected togetherby telephone lines or radio relay channels sothat all can broadcast simultaneously a pro-gram originating at a key station. Also, acamera chain.

changeover switch. A switch at a two-way com-munications point, used to shift from sendingto receiving and vice versa.

channel. A band of frequencies including the as-signed carrier frequency, within which a sta-tion is required to keep its modulated carriersignal in order to prevent interference withstations on adjacent chanels. Also, one branchor path over which signals may travel.

characteristic. The first part of a logarithm (tothe left of the decimal point). Example: Inlog 461 = 2.6637, the characteristic is 2. Thecharacteristic of a number greater than 1 ispositive and is one less than the number ofdigits to the left of the decimal point. The char-acteristic of a number less than 1 is negative,and is one more than the number of zeros im-mediately to the right of the decimal point.

characteristic curve. A curve plotted as a graphto show the relation of changing values. Forexample, a curve showing how the plate cur-rent in a vacuum tube changes with respectto a change in grid voltage.

characteristic impedance. The impedance in ohmsat the input of an infinitely long line, or of apractical line with its far end closed by amatching impedance, equal to VL/C of theline for all but very low frequencies.

charge. A quantity of electrical energy held on aninsulated object. The electrical energy storedin a condenser. The act of supplying electricalenergy to a metal object, to a condenser, or toa storage battery. When an object has moreelectrons than normal, it has a negative charge.When an object has less electrons than normal,it has a positive charge.

charger. A device for supplying direct current forcharging a storage battery.

chassis. Assembled parts .on a metal frame orbase, not including the housing or cabinet.Also, the metal frame itself.

chassis base. The metal framework on whichparts are mounted. The chassis.

chassis punch. A tool for making round or squareholes in sheet metal.

14

Child's Law. An equation stating that diode cur-rent varies directly with the three -halves powerof the anode voltage, and inversely with thesquare of the distance between the electrodes.Also known as Langmuir's equation, or thethree -halves power equation.

chip. The material removed from a phonographdisc by the recording stylus in cutting thegroove during sound recording.

choke coil. A coil used to limit the flow of al-ternating current while allowing direct currentto pass.

chopper. A device for continuously breaking upa current or a ray of light.

Christmas -tree pattern. The optical pattern ob-served when the surface of a phonograph recordis illuminated by a narrow beam of light, andindicating the quality of a recording.

chromatic aberration. The dispersive effect of alens in which light rays of different color arenot brought to the same focal point throughfailure of the lens to bend all colors of lightthe same amount.

chuck. A clamping device that holds the stylusor needle of a phonograph pickup. Also, adevice that holds a drill bit, as in a hand drillor drill press.

cipher. A zero. Also, a secret code.circuit. A complete path over which electrons can

flow from the negative terminal of a voltagesource through connecting wires and parts tothe positive terminal of the same voltagesource. Also the path taken by magnetic flux.

circuit breaker. An electromagnetic device thatopens or breaks a circuit automatically whenthe current rises above a set value.

circuit -disturbance test. A professional servicingtechnique widely used for isolating the defec-tive stage in a dead receiver. It depends on thefact that a disturbance introduced in any re-ceiver stage will reach the reproducer only ifall stages between the point of disturbance andthe reproducer are in operating condition. Thedisturbance is introduced in each stage in turn,working from the reproducer toward the an-tenna; the first stage at which no response isobtained is the defective stage.

circularly polarized wave. A polarized wave inwhich the direction of displacement rotateswith constant angular velocity about an axisin the direction of propagation.

circular mil. A unit of area used chiefly in specify-ing the cross-sectional areas of wires. Thearea of a circle whose diameter is one mil(.001 inch).

circular -mil -foot. A unit of wire measure havinga cross-sectional area of one circular mil and alength of one foot.

Civil Aeronautics Administration (CAA). A govern-ment agency charged with establishing gen-eral air traffic rules and safety regulations,and operating weather and radio beacon sta-tions, and Airways Traffic Control stations.

clamp. A device for compressing or holding to-gether two or more parts.

damper. A circuit that keeps either amplitudeextreme of a signal at a specific potential levelby inserting a dc level. The de restorer is adamper.

clamping. The process of re-establishing the dolevel or base line of a waveform after it hasbeen wiped out by ac -coupled video stages.

class A amplifier. An amplifier in which the gridbias and alternating grid voltages are suchthat plate current flows at all times.

class AB amplifier. An amplifier intermediate be-tween class A and class B in its operation. Itoperates in class A on weak signals but ap-proaches class B on strong ones. (Note: Todenote that grid current does not flow duringany part of the input cycle, the suffix 1 maybe added to the letter or letters of the classidentification. The suffix 2 may be used todenote that grid current does flow.)

class B amplifier. An amplifier in which the gridbias is approximately equal to the cut-off valueso that the plate current is approximatelyzero when no exciting grid voltage is applied,and so that plate current flows for approxi-mately one half of each cycle when an alter-nating grid voltage is applied.

class C amplifier. An amplifier in which the gridbias is appreciably greater than the cut-offvalue so that the plate current is zero whenno alternating grid voltage is applied, and sothat plate current flows for appreciably lessthan one half of each cycle when an alternat-ing grid voltage is applied.

click filter. See key -click filter.

clip. A small spring clamp used for making areadily removable connection.

clipper. In a television receiver, the circuit thatseparates the control pulses from the videosignal. Also called sync separator or ampli-tude separator. Also, a circuit for limitingthe amplitude of a signal by removing allabove a desired amplitude.

clipping. Separation of the control pulses fromthe video signals. Also, distortion in amplifiersproduced of the plate currentcurve because of excessive grid current duringthe positive grid swing. Also, distortion in theof component of a modulated wave when modu-lation amplitude exceeds that which bringsthe trough to zero. Also, generation of squarewaves by shunting biased diodes across a load,the bias determining the amplitude at whichthe peaks are to be removed.

clipping level. The amplitude level at which awaveform is clipped.

clockwise. The direction in which the hands of aclock move.

close coupling. Coupling provided by an rf or i-ftransformer when the primary and secondarywindings are as close together as possible.

coaxial antenna. An antenna that is a quarterwavelength extension of the center conductorof a coaxial cable, with the outer conductorconnected to and covered with a quarter -wave-length "skirt" or sheath.

Coaxial Cable

coaxial cable (coax). A high -frequency radio,television, or telephone transmission cable con-sisting of a central inner conductor separatedfrom a cylindrical -shaped surrounding con-ductor by an insulator.

cobalt. A metallic element often combined withiron and steel to make alloys used in perma-nent magnets. It is less magnetic than iron,but retains its magnetism at temperatures ashigh as 1100 degrees Centigrade.

15

co -channel interference. Interference from an un-desired signal having the same nominal car-rier frequency as the desired signal.

codan. (Coined from Carrier Operated Device,Anti -Noise.) A squelch circuit.

code. A system of dot and dash signals used inthe transmission of messages by radio or wiretelegraphy. The International Morse Code(also called the Continental Code) is usedeverywhere for radio telegraphy. The Ameri-can Morse Code is used commonly for wiretelegraphy. Also a system of sending secretmessages.

code recorder. An instrument that makes apermanent record of code messages.

coefficient. Any factor of a product can be calledthe coefficient of the product of the remainingfactors. Examples: In 2xy, 2 is the coefficientof xy; x is the coefficient of 2y; y is the co-efficient of 2x. Usually, however, only the nu-merical part of an expression is called the co-efficient. If there are no numbers in the ex-pression, the coefficient is assumed to be 1.

coercive force. The amount of opposite magneto -motive force necessary to eliminate residualmagnetism.

coherer. A device used in the early days of radiocommunication for detecting or rectifyingsignals by mechanical means.

Courtesy Essex ElectronicsCoil

coil. A number of turns of wire offering consider-able opposition to alternating current at thefrequencies for which it is designed.

coil form. The tubing or solid object on whicha coil is wound. It can have any shape and canbe made from any insulating material, such aspaper, cardboard, fiber, Bakelite, a plastic orceramic material, glass, or wood.

coincidence counter. A device for counting pulsesthat occur in separate circuits at precisely thesame time.

cold cathode. A cathode that does not depend up-on heat for electron emission. The cold cathodeof a photo -electric tube emits electrons whenexposed to light, and in a rectifier tube suchas the OZ4 the electrons are pulled out of thecold cathode when a sufficiently high voltage isapplied to the anode to ionize a path betweenthe two.

cold -cathode tubes. Tubes in which electron emis-sion is obtained without heating the cathode.

collector. Any electrode for capturing electrons.Specifically, a conductive coating or ring onthe inside of the glass envelope of a televisioncamera tube, midway between the mosaic andthe window end, for collecting the electronsthat leave the light-sensitive mosaic surface.

collector rings. See slip rings.

collinear antenna array. An antenna array In whichall the elements lie in the same straight line.

color. The visual sensation produced when lightenters the eye. The color perceived dependson the wavelength of the light. A wavelengthof 4000 angstrom units is perceived as violetand a wavelength of 7000 angstrom units asred, with all other color wavelengths betweenthese limits. White is seen whenever the threeprimary light colors or two complementariesare present in equal proportions.

color code. Any system of colored markings usedto indicate the electrical value of a part or toidentify terminals and leads.

color disc. A disc containing red, blue, and greenwindows, rotated in front of the televisioncamera or picture tube in a field -sequentialcolor TV system.

color drum. A cylindrical tube containing red,blue, and green windows, rotated around a pic-ture tube in a field -sequential color TV system.

color field. Scanning through the picture areaonce in the selected scanning pattern and ineach of the primary colors. In the line -inter-laced scanning pattern of two to one, it meansthe scanning of the alternate lines of the pic-ture area once in each of the primary colors.

color frame. Scanning all of the picture area oncein each of the primary colors. In the line inter-laced scanning pattern of two to one, a colorframe consists of two color fields.

color response. The relative sensitivity of photo-electric cells, TV camera tubes, and of thehuman eye to light of various colors.

Colpitts oscillator. An oscillator in which a paral-lel -tuned tank circuit is connected betweengrid and plate, with the tank capacitance con-taining two voltage -dividing in se-ries, with their common connection at cathodepotential and the necessary feedback voltagebeing obtained across the grid -cathode ca-pacitor.

communications band. The active band of fre-quencies produced by modulation or keying ofa particular transmitter. The ideal communi-cations band is narrower than a channel, toprevent interference between stations havingadjacent frequency assignments.

communications receiver. A receiver designed es-pecially for reception of code or voice messagestransmitted by radio communications services.

commutating poles. Small poles set between themain poles of a generator or motor to producesparkless commutation.

commutation. In a dc generator, the process ofchanging the generated ac voltage to a pul-sating dc voltage by means of a commutatorand brushes.

commutator. A set of copper segments radiallymounted on the armature shaft and connectedto the armature coils of a dc motor or genera-tor, with fixed brushes pressing against thecommutator segments to provide connectionsto the armature coils.

compander. A circuit for either compressing orexpanding the volume range.

compass. A small permanent magnet mounted soit can rotate freely. It will line up with theearth's magnetic lines of force, and point to-ward the north and south magnetic poles.

compatability. Ability of a color television trans-mission system to provide color service forcolor receivers, and at the same time producemonochrome pictures on existing black -and -

16

white receivers without modification of thesereceivers.

compensated amplifier. An amplifier with a fre-quency response adjusted to fit a special need.

compensated attenuator. An attenuator with as-sociated resistors and condensers, arranged toobtain or maintain a required frequency re-sponse while the amplitude is being varied.

complementary angle. Either of two angles whosesum is 90°.

complementary colors. Two colors of light, which,when properly combined, produce white light.Yellow and blue are complementary colors.

complex number. An expression consisting of areal number plus or minus an imaginary num-ber. Examples: R jx; 7 - j16. The valuefollowing j is the imaginary component.

compliance. A measure of the ability of an objectto give or stretch when a force Is applied,equivalent in a mechanical system to capacityin an electrical system. Usually used in radioIn referring to the springiness of a loudspeakermoving system.

component. Any part of a whole considered byItself. Examples : the ac portion of a pulsatingcurrent; any of the resistors, condensers, orother parts of a receiver.

components of a vector. The distances which de-termine the position of a vector with respect toreference lines. The horizontal component isthe projection of the vector upon a horizontalline, and is equal to the magnitude of the vec-tor multiplied by the cosine of the angle whichthe vector makes with the horizontal. The ver-tical component is the projection of the vectorupon the vertical line, and is equal to the mag-nitude of the vector multiplied by the sine ofthe angle that the vector makes with the hori-zontal.

composite signal. The complete television signalcontaining the picture information and thesynchronizing and blanking pulses.

composite sync signal. The portion of the televisionsignal consisting of the horizontal, vertical, andequalizing pulses.

compound. A combination of two or more ele-ments.

compound winding. A two -section field winding fora motor or generator, one section in series andthe other in parallel with the armature.

compression. Squeezing together, as in limitingthe audio -frequency response of a device toa certain portion of the normal frequencyrange, or of limiting the volume to a certainlevel. Also, a dense region of air caused by avibrating body.

concave lens. A lens with one surface curved in-ward. If the other surface is flat, it is calleda plano-concave lens; if both surfaces curveinward, it is called a double -concave lens.

concave mirror. A polished reflecting surfacecurving inward like the inside surface of asphere or ball.

concavo-convex lens. A lens that curves inward onone side and outward on the other side.

concentric. Having a common center.

concentric cable. Coaxial cable.

concentric line. A coaxial cable.

concentric -line oscillator. An oscillator whosegrid and/or plate tank inductances are formed

by the elements of a concentric line. Used inultra -high -frequency work.

condensations and rarefactions. Periodic increasesand decreases in air pressure resulting fromthe pulsation or vibration of some soundsource. The condensations and rarefactionstraveling outward from the source constitute asound wave.

condenser. Two conducting surfaces separatedby an insulating material, such as air, oil,paper, ceramic, or mica. A condenser is capa-ble of storing electric energy, and is usedto block the flow of direct current while al-lowing alternating and pulsating currents topass. The electrical size or capacity of a con-denser is specified in microfarads and micro-microfarads.

condenser bank. A number of by-pass or filtercondensers in a single container.

condenser gang. A number of variable condensersoperated from the same shaft.

condenser loudspeaker. A loudspeaker in whichthe mechanical forces moving the diaphragmresult from electrostatic interactions of twolarge, closely spaced plates when a varyingsignal voltage is applied to the plates.

condenser microphone. A microphone consistingessentially of a flexible metal diaphragm anda rigid metal plate arranged to form a two -plate condenser. Sound waves set the dia-phragm in vibration, varying the capacity,which in turn causes a varying current flowfrom the source of charging voltage.

condenser, voltage -regulating. A condenser, usual-ly of the wet electrolytic type, used in a cir-cuit to limit voltage rises by placing a loadon the circuit if the voltage goes too high.

conductance (G). The characteristic of a bodythat allows electricity to flow through it. Theunit of conductance is the mho. Conductance isthe reciprocal of resistance; that is, when re-sistance is lowered, the conductance is propor-tionally increased.

conduction current. A current formed by move-ments of electrons only (not ions).

conductivity. The conductance of a unit cube ofa material.

conductor. A material that offers little oppositionto the flow of electric current. A wire or metalstructure that provides a path for electric cur-rent between two points.

conduit. A metal pipe through which electricalconductors are run.

cone. The conical -shaped paper or fiber dia-phragm of a magnetic or dynamic loudspeaker.

ConeCourtesy Jensen

1Z

cone of silence. The area directly over the antennaof a radio beacon transmitting antenna, inwhich no signal can be picked up.

confetti. The effect of random noise on the re-produced picture in color TV. Corresponds tosnow on a black -and -white picture.

conical antenna. An antenna consisting of twocones, placed apex to apex, or two pairs ofwires arranged in a flattened X to resemble theoutlines of such cones.

conical horn. A cone -shaped horn, having a radiusthat increases uniformly along the axis of thehorn.

connector. Any device that joins or couples twoor more parts.

console. A large receiver cabinet designed to reston the floor rather than on a table. Also, thedesk on which are mounted the controls of atransmitter.

constant. A quantity expressing a value that doesnot vary.

constant -amplitude recording. A recording inwhich signals having the same power are in-scribed at the same amplitude regardless offrequency.

Constantan. An alloy of approximately 60% cop-per and 40% nickel, used in the constructionof precision resistors, rheostats, and measur-ing instruments.

constant -current generator. A tube circuit in whichthe ac plate resistance is high compared to theplate load resistance, with the result that thecurrent is practically independent of loadvariations.

constant -current modulation. Amplitude modula-tion in which the output circuits of the modu-lator and the modulated amplifier are coupledby a common inductor that has high impedanceto the signal frequencies and which, therefore,maintains the common plate supply current ofthe two circuits constant. The signal -frequencyvoltage appearing across the common induc-tor appears also as modulation of the plate sup-ply to the modulated amplifier with corre-sponding modulation of the carrier output.

constant -current transformer. A transformer de -designed so that the current at the secondaryremains constant under varying loads when aconstant voltage is supplied to the primary.

constant -velocity recording. A recording in whichthe amplitude of the cut in the record is in-versely proportional to the frequency in orderto hold the vibrational velocity constant.

constant -voltage transformer. A transformer de-livering a fixed voltage regardless of inputvoltage variations over a limited range.

contact. A terminal to which a connection can bemade. A junction of conductors to permit theflow of electrical current.

contact emf. See contact potential.contact microphone. A microphone designed to

pick up mechanical vibrations directly and con-vert them into electrical impulses.

contact potential. A small voltage that is estab-lished whenever two conductors of differentmaterials are brought into contact. It is dueto the difference in work functions or the easewith which electrons can cross the surfaceboundary in the two directions.

contact rectifier. Two different solids in contact,in which rectification is due to greater con-

ductivity across the contact in one directionthan in the other.

contact resistance. The ohmic resistance betweenthe contacts on a switch or relay.

Continental Code. The International Morse Code.

continuity. The property of having a continuousor complete dc electrical path.

continuous duty rating. Classification of a part, in-dicating the conditions under which it is ca-pable of uninterrupted use or operation.

continuous spectrum. A spectrum whose com-ponents are continuously distributed over afrequency region.

continuous wave (cw). A radio wave in which suc-cessive cycles are identical (constant in ampli-tude) under steady-state conditions.

contrast. The range in light values between thebrightest and the darkest elements in a picture.

contrast control. An adjustment for increasingor decreasing the range of light intensities ofan image by varying the amplitude of the pic-ture signal. Contrast control in the televisionreceiver corresponds to gain control in a soundreceiver.

control characteristic. A relation, usually shownby a graph, between the critical grid voltageand the anode voltage in a gas -filled tube.

control electrode. An electrode to which a varyingvoltage is applied for the purpose of varyingthe current flowing between two or more otherelectrodes in a vacuum tube.

control grid. That electrode in a vacuum tubewhich has the most effective control over theplate current passed by the tube.

controlled carrier modulation. Compound modula-tion in which the carrier amplitude is variedin accordance with the degree of modulationas averaged over a short period of time. Whenthe modulation is small, the carrier amplitudeis small, but when the modulation is increased,the carrier is increased accordingly, so thatthe percentage of modulation, or modulationfactor, remains relatively constant regardless -of the amplitude of the signal.

control room. A room in a station, from whichthe engineers and production men monitor andcontrol the program, usually partly or com-pletely enclosed in glass and located next tothe main studio.

convection current. A current in which the elec-tricity is carried by masses heavier than elec-trons (ions).

converge. To bring together, as to focus lightrays or radio waves to a single point.

convergent beam. A beam of light whose raysmeet (converge) at a single point.

conversion transconductance. The ratio of the de-sired beat frequency component of the platecurrent to the signal voltage applied to thegrid.

converter. The section of a superheterodyne radioreceiver that changes incoming modulated rfsignals to a lower frequency known as the i-fvalue. Also, a device, usually rotary, for chang-ing electrical energy from one form to another,as ac to dc. Also, a device for changing thefrequency of incoming signals to values thatcan be tuned in by the receiver.

converter noise. Noise generated in the mixer -first detector of a superheterodyne receiver.

1$

convex lens. A lens with one surface curved out-ward. If the other surface is flat, it is calleda piano -convex lens; if both surfaces curveoutward, it is called a double -convex lens.

convex mirror. A polished reflecting surface curv-ing outward like the outside of a sphere.

coordinate. Any of two or more magnitudes thatdetermine the position of a point with respectto reference lines. Ordinary graphs userectangular coordinates, in which the hori-zontal reference line is called the X axis or theaxis of abscissa, and the vertical reference lineis called the Y axis or the axis of ordinates.In polar coordinates, position is determinedwith one vector magnitude and the angle thevector makes with the horizontal referenceline or X axis.

copper. A metallic element widely used in elec-trical equipment. It is one of the best con-ductors of both electricity and heat.

copper -oxide rectifier. A rectifier made up of discsof copper coated on one side with cuprousoxide. The discs allow current to flow in onedirection but allow very little current flow inthe reverse direction.

copper -oxide rectifier -type meter. An instrumentfor measuring ac voltages and currents, usinga copper -oxide rectifier to convert ac to dc toactuate a dc -indicating d'Arsonval type meter.

cord. A highly flexible wire, usually stranded,and insulated to withstand wear.

core. The material or space about which a coilis wound; by extension, the material throughwhich flows the major portion of the magneticflux.

core losses. The losses in an iron -core coil ortransformer due to eddy currents and hys-teresis in the iron core.

corona. The discharge of electricity that appearson the surface of a conductor as a glow ofcolored light when the potential gradient (volt-age per unit length) exceeds a certain value.It is due to ionization of surrounding air bythe high voltage.

corrosion. A chemical action, oxidation or rust-- ing, which causes a gradual wearing away of

metal.

corrugated. Having a surface with alternatevalleys and ridges.

cosecant (csc). A trigonometric function. Thecosecant of an acute angle of a right triangle(written csc 8) is equal to the hypotenuse di-vided by the opposite side.

cosine (cos). A trigonometric function. Thecosine of an acute angle of a right triangle(written cos 0) is equal to the adjacent sidedivided by the hypotenuse.

cosmic rays. Rays originating outside the earth'satmosphere, having extremely high frequencyand penetrating power.

cotangent (cot). A trigonometric function. Thecotangent of an acute angle of a right triangle(written cot 0) is equal to the adjacent sidedivided by the opposite side.

coulomb. A unit of measure of the quantity ofelectricity that passes a given point at a giventime. A coulomb is the quantity that is trans-ferred by a current of one ampere flowing forone second, which Involves a movement of 6.3million, million, million electrons past a pointin the circuit.

Coulomb's Law. The force of attraction or repul-sion between two charges (or magnetic poles)

Is directly proportional to the product of thecharges (or pole strengths), inversely propor-tional to the square of the distance betweenthem, and is modified by the dielectric con-stant (permeability) of the material betweenthem.

counter. A frequency divider used to reduce thenumber of pulses to an amount capable of be-ing handled by some mechanical countingdevice.

counterbore. To drill a cylindrical, flat-bottomedhole for receiving the head of a screw so thatit will be flush with or below the surface ofthe work.

counter -clockwise. In a direction opposite that inwhich the hands of a clock rotate.

counter emf. See back electromotive force.counterpoise. A system of wires directly below a

transmitting antenna, insulated from and re-placing the ground where the ground conduc-tivity is poor or where the terrain prevents theuse of sunken wires.

countersink. To ream, drill, or cut a conical de-pression around a hole for a flat -head screw,so that the screw head will be flush with orbelow the surface of the work.

counting circuit. See counter.

coupled circuits. Separate circuits that are madeto influence one another.

coupler. An inductive, capacitive, or resistive de-vice used to transfer electric power from onecircuit to another.

coupling. The means by which signals are trans-ferred from one radio circuit to another.Coupling can be direct through a conductor,electrostatic through a condenser, or inductivethrough a transformer. Optimum coupling orcritical coupling is that which gives maximumtransfer of signal energy. Tight coupling isthe closest possible coupling under a givenset of conditions. Loose or poor coupling giveslittle transfer of signal energy. Also a devicefor connecting two shafts together end to end.

coupling coefficient. A numerical rating between 0and 1, specifying the degree of coupling be-tween two circuits. Perfect coupling is 1, andno coupling is 0. For inductive coupling, thecoupling coefficient is equal to M -;- VIA L2,where M is the mutual inductance in henrys,and Li and L2 are the inductance values inhenrys of the individual coils.

coupling condenser. A condenser used to coupletwo circuits together.

coupling transformer. A transformer used to coupletwo circuits together by means of mutual in-duction.

C power supply. Any power -supply device con-nected between the cathode and grid of a vac-uum tube so as to apply a grid bias, such as aC battery or grid bias cell.

crater. The cavity formed in the positive carbonelectrode of an electric arc. The highest lightintensity is emitted in the region of the crater.

crater lamp. A neon lamp having a cup -shapedlight source, providing a spot source of light.

critical angle. The angle of incidence beyondwhich rays of light are no longer refracted(bent) into a transparent medium, but aretotally reflected from its surface..

critical coupling. Coupling that produces maxi-mum transfer of energy.

19

Courtesy Astatic Corp.Crystal Cartridges

critical damping. Introduction into a series LCcircuit of that value of R that will cause atransient to die out within a half cycle, with-out producing oscillations.

critical grid voltage. That value of voltage on thegrid of a thyratron which, if increased slightlyin the positive direction, will cause the tubeto fire.

critical viewing distance. The distance at whichthe l'ine structure of a television image be-comes indiscernible.

crocodile clip. A long -nosed clamp with spring -controlled jaws, one of which is smaller thanthe other so that the teeth do not mesh, usedon test leads for making quick, temporary con-nections.

cross modulation. A type of station interference(intermodulation) in which the carrier of adesired signal becomes modulated with an un-desired signal, so that the undesired signal isheard.

cross neutralization. A method of neutralizationused in push-pull amplifiers whereby part ofthe plate -cathode ac voltage of each tube isapplied through a neutralizing capacitor to thegrid -cathode circuit of the other tube.

cross -over area. In an electron gun, a region inthe first lens system where emitted electronsare brought together under the influence ofelectric (and sometimes magnetic) fields.

cross -over frequency. The frequency where theoutput from a low -frequency speaker and ahigh -frequency speaker are equal. Below thispoint, the output is primarily from the low -frequency speaker; above it the output is fromthe high -frequency speaker.

cross -over network. A circuit used to divide thehigh and low frequencies for application to adual loudspeaker system.

cross -over point. The point at which converginglight rays or electron beams cross and beginto diverge.

cross-section. The area of that part of an objectthat is contained in any plane at right anglesto the object length.

cross -talk. Audio -frequency interference existingbetween adjacent telephone lines. Also, cross -modulation.

cruciform core. A type of transformer core havingthe primary and secondary windings on a cen-tral core, with four separate magnetic returnpaths.

crystal. A piece of natural quartz or similarpiezoelectric material that when set into vi-bration will generate a voltage at a desiredradio frequency. A quartz crystal is used inradio transmitters to generate the assignedcarrier frequency of a station, and in filtersof radio receivers to improve the selectivity ofthe i-f amplifier. Also, the mineral used in acrystal detector is known as a crystal.

crystal cartridge. A case or shell containing apiezoelectric crystal, usually of Rochelle salt,used in a phonograph pickup to convert me-chanical movement of the needle into electricenergy.

crystal control. Use of a quartz 'crystal to main-tain operation of a radio station at its assignedfrequency within the limits prescribed by law.

crystal -controlled transmitter. A transmitter whosecarrier frequency is directly controlled by theelectro-mechanical characteristics of a crystal.

crystal detector. A detector consisting of a crystalsuch as silicon, germanium, or galena in con-tact with a pointed wire.

crystal filter. A highly selective tuning circuitusing a quartz crystal, sometimes used in thei-f amplifier of a communications receiver toimprove selectivity.

crystal holder. A device to hold a quartz crystalin a definite position and provide proper elec-trical contacts for it. Some holders have avariable air gap so the frequency of oscillationcan be varied over a limited range.

crystal loudspeaker. A loudspeaker in which themechanical forces acting on the diaphragmresult from the vibration of a crystal element.

crystal microphone.' A microphone in whichchanges in the shape of a piezoelectric crystalcaused by sound waves generate the outputvoltage.

crystal oscillator. A vacuum -tube oscillator stagewhose frequency is determined by a piezoelec-tric (quartz) crystal.

crystal oven. A small electrically heated oven inwhich the quartz crystal of a transmitter ismounted. The oven and crystal are kept atessentially constant temperature by automatictemperature controls to prevent frequencydrift with temperature change.

crystaJ pickup. A phonograph pickup in whichchanges in the shape of a piezoelectric crystalby movements of the phonograph needle gen-erate the output voltage.crystal set. A radio receiver using a crystal de-tector for signal rectification.C supply. Grid -voltage supply.cube. The third power of a number, obtained by

using a number as a factor three times. Ex-ample: 3 X 3 X 3 -= 27, which is the cubeor third power of 3.cube root. A number which, when multiplied by

itself three times, equals the given number.Examples: 3 is the cube root of 27: 5 is thecube root of 125. Cube root is indicated bya radical sign with 3 as the index number.Example: V343.

current. The movement of electrons through aconductor. Current is measured in amperes,milliamperes, and microamperes.

current antinode. A point along a transmissionline or antenna at which current is at a maxi-mum.

current density. The amount of an electric currentper unit cross-sectional area of a conductor.

current feed. A method of exciting a transmittingantenna by feeding current to it at a point ofminimum impedance.

current feedback. A form of degeneration in20

which the feedback is proportional to the platecurrent.

current -limiting resistor. A resistor used in a cir-cuit as a protective device against overloadduring voltage surges.

current loop. See current antinode.current node. Any point in a transmission line

or antenna that has zero current.

current transformer. A transformer connected in-to a high -current circuit to permit measure-ment. A meter is connected across the sec-ondary winding, and is calibrated or read interms of current flowing in the primary.

curve. The line on a graph that connects plottedpoints and shows the relationship of one vari-able to another.

curvilinear cone. A curved loudspeaker cone hav-ing the general form of a parabola, used tosecure pure piston action. A para-curve.

cushion socket. A tube socket mounted on softrubber or springs, so that vibration will notinjure or affect the tube.

cut. Removal of spoken or musical material froma radio program script in order to fit the pre-scribed time. Also, a command telling thestudio engineer to disconnect all microphones,so nothing more can go out on the air.

cut-off. In a vacuum tube, the grid -bias voltagevalue at which plate current ceases to flow.Also, in a selective circuit, the frequency aboveor below which an amplifier or circuit fails torespond. Also, the lowest frequency a waveguide can transmit.

cut-off frequency. That frequency in a filter, loud-speaker, or other system at which rapid, if notcomplete, attenuation takes place,

cut-off voltage. Negative grid bias at and beyondwhich plate current ceases to flow.

cutout. Any arrangement by which a circuit isautomatically opened when the current flow-ing through it exceeds or drops below a certainset value. Usually an electromagnetic devicelike a relay.

cutter. In recording, the device that transformselectric energy into mechanical motion. whichis then inscribed into the record by the stylus.

cutting angle. Angle between the vertical cuttingface of the stylus and the record surface.

cutting head. That part of a sound recorder whichcuts or embosses on a disc the irregular groovescorresponding to the wave form of the soundsbeing recorded.

cutting stylus. The tool that cuts the groove intoa record during recording.

cycle. One complete round of a regularly recur-ring event. Specifically, of an alternating cur-rent, the rise from zero to a maximum in onedirection, a return to zero, a rise to a maximumin the opposite direction, and another returnto zero. The number of cycles occurring in onesecond is the frequency of an alternating cur-rent. The word cycle is commonly used tomean cycles per second, which is the measureof frequency.

cyclotron. An apparatus that uses electromagneticand electrostatic means for imparting tre-mendously high speeds to electrified particles.Cyclotrons are used to bombard the nuclei ofatoms so -as to change atomic structure orartifically produce radioactivity.

cylindrical antenna. See coaxial antenna.

cylindrical concave mirror. A curved reflectingsurface like the Inside of half a cylinder, usedto focus light rays to a line.

cylindrical convex lens. A long lens having onesurface curved outward and the other one flat,used to focus light rays to a line.

Ddamped waves. Radio waves that progressively

decrease in amplitude during successive cycles.

dampen the studio. To increase the absorption ofsound in a studio by using sound -absorbingequipment such as monk's cloth screens,drapes, or rugs, or by bringing more peopleinto the studio.

damping. Dissipation of energy in such a waythat oscillations or vibrations die out rapidly.

damping tube. In television, a tube connectedacross the horizontal deflection coils to cutoff shock -excited oscillations when the mag-netic field collapses.

dark spot defect. Dark areas in the reproducedtelevision image caused by electron clouds infront of the mosaic screen in the camera tubeat the transmitter.

d'Arsonval meter movement. The meter move-ment most commonly used in direct -currentmeasuring instruments. It consists essentiallyof a small coil of wire supported on jeweledbearings between the poles of a permanentmagnet, with a spiral spring holding the coiland the attached indicating pointer at the zeroposition on the meter scale. When the currentto be measured is sent through this coil, themagnetic fields of the coil and magnet inter-act to cause rotation of the coil and pointer.

db meter. An ac voltmeter designed for use acrossa specific impedance, whose scale is calibratedto read decibel values. Used with audio ampli-fiers particularly to indicate volume level inbroadcast and public address work.

de amplifier. A direct -coupled signal amplifierthat will pass the de component along with ac.

dc component. The part of the video signal causedby the average background illumination of thescene being televised. Also, the dc portion ofany pulsating current.

dc generator. A rotating machine that convertsmechanical energy into direct -current electricenergy.

dc inserter stage. A television transmitter stagethat introduces a dc component (the pedestallevel) into the television signal. Synchronizingpulses then swing the signal in one directionfrom the pedestal level, while picture elementsswing the signal in the other direction, thusmaking it possible to separate the two at thereceiver.

dc plate resistance. The opposition to de offeredby the plate -cathode space of a vacuum tube,equal to the average or dc plate voltage dividedby the average or dc plate current.

de receiver. A receiver designed to operate froma dc power line, such as from the 110 -volt delines still being used in older sections of somecities.

do reinsertion. The process of re-establishing thedc level or base line of a waveform, after it hasbeen wiped out by ac -coupled video stages.Clamping.

de resistance. The opposition offered by a circuit

21

or component to dc current flow, measured inohms.

dc restoration. See do reinsertion.

de restorer. A circuit used to reinsert the do com-ponent of the video signal lost during ampli-fication. A clamper.

do transmission. The transmission of a televisionsignal with the direct current component inthe picture signal.

do voltage. A voltage that sends a direct currentthrough a circuit, and hence forces electronsaround the circuit in the same direction all thetime.

deadbeat. Instruments whose pointers move to aposition without undue oscillation and cometo a dead stop. A highly damped meter move-ment.

dead -center position. The position in which abrush would be placed on the commutator ofa dc motor or generator if there were no dis-tortion of field flux by armature reaction.

dead end. The part of a radio studio that hasthe greatest sound absorption. Also the por-tion of a tapped coil through which no currentis flowing.

dead receiver. A receiver that will not play.dead spot. A region in which signals from certain

stations are received poorly or not at all.decade box. A system of series -connected re-

sistors of such values that any desired amountof resistance from 1 ohm to the maximum ofthe system can be obtained in 1 -ohm steps.

decay curve. A curve showing the rate of de-crease in power, voltage, or current in a cir-cuit in which energy is being dissipated.

deci. A prefix meaning one -tenth.

decibel (db). A unit for expressing a power ratio,equal to 10 times the common logarithm of thepower ratio. One decibel is the amount bywhich the pressure of a pure sine -wave soundmust be changed in order for the change to bejust barely noticeable by the average humanear. A decibel can express an actual level onlywhen some definite reference level is assumedto be zero db. With sound, the threshold ofaudibility is generally assumed to be zero db,and in public address work a power of 0.006watt is most generally used as the referencelevel of zero db. In broadcasting, 0.001 wattis used as the zero level.

decimal fraction. A proper fraction in which thedenominator is some power of 10, usually ex-pressed by a period (decimal point) placed atthe left of the numerator.

decineper. One -tenth of a neper.

deck switch. A gang switch in which sets of con-tacts are arranged at different levels on insu-lating rings, with the contact points or fingerson discs attached to a shaft.

decoupling. Means taken to prevent couplingbetween stages or circuits of a stage.

decoupling circuit. A network of resistors or coilsand capacitors used to separate and by-passsignals that would ordinarily flow in a com-mon circuit.

decrement. The decrease in the value of a variablequantity.

de -emphasis. The reduction of some part of asignal, as the restoration of a pre -emphasizedsignal wave to its original form.

de -emphasis circuit. A circuit that reduces somepart of a signal, as an R -C filter in an FMreceiver that decreases to normal proportionsthose high audio frequencies that were empha-sized in transmission to obtain a better signal-to-noise ratio.

definition. Clarity or degree of perfection of trans-mission and reception.

deflecting coil. A coil of wire used to control byelectromagnetic means the movement of theelectron beam in a cathode-ray tube in an os-cilloscope, television camera, or television re-receiver. Also called a deflecting yoke.

deflecting plates. Pairs of metal plates in an elec-trostatic cathode-ray tube to which potentialsare applied to move the electron beam.

deflection. A movement of an object away fromits normal position, such as deflection of ameter pointer or an electron beam in a cath-ode-ray tube.

deflection factor. In electrostatic -deflection tubes,the voltage required between a pair of deflec-tion plates to produce unit deflection. Usuallyexpressed in dc volts per inch. In magnetic -deflection tubes, the current required througha definite deflection yoke at a definite pointon the tube to produce unit deflection. Usuallyexpressed in milliamperes per inch.

deflection sensitivity. The beam deflection in acathode-ray tube caused by a given change inthe field intensity.

deflection yoke. An assembly consisting of thehorizontal and vertical deflection coils of amagnetically deflected picture tube.

Deflection Yoke

Courtesy RCA

degaussing. Neutralizing the magnetic field, as ofa ship so that if it passes over a magneticmine, the striker on the mine will not act andthe mine will not explode.

degeneration. The feeding back of an out -of -phasesignal so that the effective amplification is re-duced. Deliberately introduced in inversefeedback circuits because it reduces distortion.

de -ionization. Reversion of ions in a glow or arcto their original condition as neutral atoms andmolecules.

de -ionization time. The time required for the gridof a gas tube to regain control after plate cur-rent has been interrupted.

delayed avc. An automatic volume control circuitthat does not begin to act until signals reacha certain strength. It permits reception of weaksignals even though they are fading, whereasnormal avc tends to make weak signals weaker.

delta antenna -matching transformer. A means ofmatching the impedances of an open -wire trans-mission line and a half -wave antenna by spread-ing out the upper ends of the line and con-necting them directly to the antenna to forma triangle like the Greek letter delta (A).

delta circuit. A network of three resistors or im-22

pedances connected in the form of a trianglelike the Greek letter delta (A).

delta connection. Connections forming a trianglelike the Greek letter delta (A).

demodulation. The process of rectifying or de-tecting a modulated radio signal in order toremove the carrier and obtain the desired audioor picture signal.

denominator. The part of a fraction written belowthe line. Example: In 1/2, the denominator is 2.

densitometer. An instrument used to measure thedensity or opacity of a material.

density. A measure of the concentration of matterin a material, in which case density is equalto weight divided by volume. Current densityis the total current divided by the cross-sec-tional area of the conductor.

depolarization. Removal of the gases that format the electrodes in a battery as a result ofthe chemical action involved in producing cur-rent.

depolarizer. The chemical used in a primary cellto reduce polarization by removing the hydro-gen gas formed at the carbon electrode.

detection. The process of obtaining the desiredintelligence from a modulated carrier. Seedemodulation. Also, frequency conversion as ina superheterodyne receiver.

detector. The stage in a receiver in which de-modulation or detection takes place.

detent. A mechanism used on indexed rotaryswitches to hold the switch firmly in position.Generally consists of a spring -loaded ball thatfalls into place in indentations on a plate thatrotates with the switch shaft.

detune. To change slightly the capacity, the in-ductance, or both in a tuned circuit, so that itno longer is in exact resonance at the appliedfrequency.

deviation, frequency. See frequency deviation.deviation ratio. The ratio of maximum frequency

deviation to the highest audio frequency inan FM signal.

diagram. A plan or layout for a receiver, trans-mitter, or other apparatus. In a schematic cir-cuit diagram, schematic symbols representradio parts. In a pictorial circuit diagram, ac-tual sketches of radio parts are used. In a blockdiagram, entire circuits, stages, or sections arerepresented by labeled blocks.

dial. Any means for indicating the value to whicha control knob has been adjusted.

dial cord. The braided cord or flexible wire cableused to make a tuning knob control the posi-tion of the pointer or dial that indicates thefrequency or channel to which a receiver istuned.

dial light. The pilot lamp that illuminates thetuning dial of a receiver.

diameter. A line passing through the center of acircle and ending at opposite points on thecircle. The distance across, or width of thecircle.

diaphragm. A thin, flexible sheet that can pro-duce sound vibrations (as in a headphone) orcan be moved by sound waves (as in a micro-phone). In photography and in television cam-eras. an adjustable device used to reduce theeffective area of a lens so as to control theamount of light passed by the lens.

diathermy. Therapeutic use of a high -frequency

current to generate heat within the body. Dia-thermy machines are actually short-wave trans-mitters, and often cause serious radio and TVinterferer ce.

dichroic mirror. A glass surface treated withmetallic salts that reflects only one color andpermits all other colors to pass through theglass.

dielectric. The insulating material between twoconductors. Specifically that between the platesof a condenser.

dielectric constant. The ratio of the capacity of acondenser using a given substance for a dielec-tric to the capacity of the same condenser withair for a dielectric.

dielectric loss. Energy loss in the form of heat inthe dielectric of a capacitor, due to an actionsimilar to hysteresis in a magnetic circuit.

dielectric strength. The voltage a dielectric of unitthickness can withstand without breakingdown.

differentiating circuit. A high-pass filter. A cir-cuit in which the voltage amplitude at theoutput is proportional at any instant to therate of change of voltage amplitude at theinput. Specifically, such a circuit used in a TVrecei"er to segregate the horizontal sync pulsesfrom the vertical sync pulses after clipping.

diffraction. The spreading of an electromagneticwave or light beam into the region behind anobstacle.

diffusion. Scattering of light or electromagneticwaves.

diheptal base. A 14 -pin tube base used forcathode-ray tubes.

dimmer. A device by means of which lights maybe gradually dimmed or brightened.

diode. A vacuum tube having two electrodes, onethe cathode and the other the plate or anode.

diode -pentode. A vacuum tube having a diodeand a pentode in the same envelope.

diode -triode. A diode and a triode in the sametube envelope.

diopter. A unit expressing the power of a lens,equal to the reciprocal of the focal length inmeters.

diplexer. A coupling unit that allows two trans-mitters to operate simultaneously into thesame antenna.

dipole. An object oppositely charged at twopoles, especially an antenna shorter than ahalf wavelength. Loosely, an antenna whoselength is approximately one half of the elec-tromagnetic wavelength to which it is resonant.

Dipole

23

direct coupled amplifier. An amplifier in which thestages are coupled without the use of con-densers or transformers, so that there is adirect or de path between the stages.

direct current (de). An electric current that flowsin only one direction, not necessarily constantin value.

direct Inductive coupling. A method of coupling inwhich one circuit is connected directly to atap on the inductance element of another cir-cuit.

directional antenna. An antenna that radiates orreceives radio waves better in some directionsthan others.

directional pattern of an antenna. A special graph(polar characteristic) that indicates the in-tensity of the radiation field of a transmittingantenna at a fixed distance in different direc-tions In space. In the case of a receiving an-tenna, it indicates the response of the antennafrom different directions to a signal havingunit field intensity.

direction finder (df). A radio -receiving device usedto determine the direction of the source ofelectromagnetic waves.

direction -finder deviation. The difference betweenthe observed bearing and the true (corrected)bearing of a direction finder.

direction of polarization. The direction of the elec-tric field component in an electromagneticwave. For example, a vertically polarized waveis one having the electric field component ina vertical (up and down) plane with respectto the earth's surface.

directly proportional. Varying in the same direc-tion as some other value. For example, if oneincreases, so does the other.

director. In a directional antenna system, theparasitic element in front of the antenna thatincreases the radiation or reception along aline passing through it to the antenna.

direct scanning. A system in which the entiresubject is illuminated, and a scanning deviceis used in front of a light-sensitive cell to ex-pose a limited area of the scene at a time.

direct -view. A television receiver in which theimage is viewed on the face of the cathode-raytube. Distinguished from the indirect -view orprojection -type receiver, in which the imageis optically projected from the cathode-raytube to a special viewing screen.

direct wave. A wave propagated through spacewithout being reflected.

directivity. The antenna characteristic thatcauses it to radiate or receive more power incertain directions than in others.

disc. A phonograph record or blank. Also, therotating element of a mechanical televisionscanning system.

discharge. A release of stored energy from acondenser, or the drawing of current from abattery.

discharge tube. A tube so operated that it isnormally cut off, but is made to conduct atperiodic intervals.

discriminator. The stage of an FM receiver thatconverts FM signals directly into audio signals.Also, a similar stage in an automatic frequencycontrol system that produces the control volt-age.

dispersion. The separation of white light into itscomponent colors, as in a prism. Also, thescattering of electromagnetic waves.

dissector. A pickup tube used in the televisioncamera, more properly an image dissector.

dissipation. Energy expended in the form of heatin the resistive elements in or associated witha circuit.

distortion. Improper reproduction of sound orimage because of changes occurring in thewaveform of the intelligence signal somewhereIn the path it takes through the transmittingand receiving systems or through an amplifiersystem.

distress frequency. The frequency allotted by in-ternational agreement to distress calls. Forships at sea and aircraft over the sea, it is500 kilocycles.

distress signal. By code: SOS: by radiotelephone:"MAYDAY," from the French "M'Aider,"meaning help me.

distributed capacity. Capacity distributed betweenconducting elements, as distinguished from ca-pacity concentrated in a condenser. Usually,the small capacity existing between the turnsof wire in a coil.

distributed constants. Constants that exist alongthe entire length or area of a circuit, such asdistributed capacity or distributed inductance.

distributed inductance. The inductance that existsalong the entire length of a conductor, as dis-tinguished from self-inductance concentrated incoils.

distribution. The degree of linearity of scanningin a television system. When scanning islinear, distribution is good,

distribution control. The control that varies theamount of correction applied to the sawtoothwave in a television receiver so as to give thedesired linear scanning of lines.

divergent. Spreading out from a point of origin,as of light rays or radio waves.

divergent beam. A beam of light whose raysspread out.

diversity reception. Reception of radio signals soas to overcome fading by means of two ormore antennas separated by several wave-lengths or differing in polarity.

dividend. A number or quantity that Is to bedivided. Example: In the expression 140070 = 20, the dividend is 1400. (The divisor hereis 70, and the quotient is 20.)

dividing network. See cross -over network.

division. The process of finding how many timesone number is contained in another. The stand-ard sign that indicates division is -i- . In al-gebra, a horizontal line (or sometimes a frac-tion bar) is used instead of the conventionaldivision sign. Example: E R, E and E/R

Rall mean that E is to be divided by R. Individing positive and negative numbers, thequotient is positive if both numbers have likesigns, and the quotient is negative if the num-bers have unlike signs.

divisor. The number by which a number orquantity is to be divided. Example: In 1400 ÷70 = 20. the divisor is 70. (The dividend hereis 1400, and the quotient is 20.)

dog house. The structure at the base of a trans-mitting antenna that houses the antenna tun-ing equipment.

Doherty amplifier. An amplifier circuit in whichone tube supplies unmodulated carrier power,and a second tube, feeding the same load as

24

the first, is biased so no plate current flowsuntil the rf grid voltage (modulated carriersignal) exceeds its bias. When this happens.the second tube feeds power to the load, andthe effective impedance of the load is lowered.This results in an increase in power from thefirst tube.

dolly. A perambulator, or carriage upon whicha camera is mounted.

doorknob tube. A doorknob -shaped tube designedfor ultra -high -frequency work by the elimina-tion of a base and reduction of interelectrodecapacities.

doppler effect. An apparent change in the fre-quency of a sound or electromagnetic wavereaching an observer, due either to motion ofthe source toward or away from the observer,to motion of the observer, or both.

dot interlacing. A method of scanning in whichalternate picture elements are scanned duringeach field. In color systems every third elementis scanned in one color in one field.

dot sequential. In color TV, the process of scan-ning one picture element in one primary color,the next in another, and the third in the thirdcolor. By dot interlacing each element is scan-ned In a different color in different fields, sothat when a complete frame has been scanned,each element has been scanned in all threecolors. A similar system of scanning pictureelements in some regular, repetitive patternmay be used in black and white TV.

double -button carbon microphone. A carbon micro-phone having two buttons or containers forcarbon granules, one on each side of the dia-phragm, to secure a push-pull action forincreased signal output.

double -concave lens. A lens with both sides curvedinward, so the center is the thinnest section.

double -convex lens. A lens with both sides curvedoutward, so that the center of the lens is thethickest portion.

double diode. Two diodes in the same tube en-velope. A duodiode.

double -hump resonance. A condition in which twocircuits normally resonant to the same fre-quency, are closely coupled, or are detuned sothat they resonate to frequencies on either sideof the original resonant point, thus producinga response curve having two humps.

double modulation. The process in which a carrierwave of one frequency is first modulated by thesignal wave, and is then made to modulate asecond carrier wave of higher frequency.

double -pole switch. A switch that simultaneouslychanges connections in two separate circuitsor in both sides of the same circuit.

doubler. A vacuum -tube circuit in which the out-put signal is twice the frequency of the inputsignal. Also a voltage -doubler.

double sideband transmission. A system in whichboth sidebands, one on either side of the car-rier, are transmitted. It is the standard broad-cast transmission.

double -spot tuning. The condition in which thereare two different points at which the tuningdial may be set to receive the same station.

double superheterodyne. A superhet in 'which fre-.quency conversion occurs twice. It uses twofirst -detector stages and one or two local os-cillators. A local oscillator signal is combinedwith the desired signal in the first first -detectorto produce a preliminary i-f value, and this iscombined in the second first -detector with thesame or another local oscillator signal to pro-

duce the final i-f value. Used to get more gainand to stabilize operation at high frequencies.

doublet antenna. An antenna system, independentof the earth, usually a half wavelength long orsome multiple of this length. The term is alsoused to describe a shorter antenna that shouldbe called a dipole

double -throw switch. A switch that connects oneterminal to either of two other terminals.

double triode. Two triodes in the same tube en-velope. A duotriode.

down lead. The wire connecting the antenna withthe receiver. A lead-in.

downward modulation. Modulation in which theaverage amplitude of the output is less thanthe unmodulated carrier amplitude.

Dow oscillator. An electron -coupled oscillator cir-cuit.

drain. The current being taken from a voltagesource.

D region. The region of the ionosphere up toabout 55 miles above the earth's surface.

dress. To arrange in an exact manner, as to posi-tion wires or parts so as to prevent or reduceundesired feedback.

drift. Detuning due to time, temperature, hu-midity, or other influences.

drift space. The space between the buncher andcatcher grids in a Klystron in which the elec-trons actually bunch because of their differingvelocities.

drive belt. A belt used to transmit power fromthe driving to the driven device.

drive holes. Holes spaced around the center holeof a recording disc to engage a drive pin inthe turntable, preventing the disc from slip-ping during recording or playback.

driven element. Any antenna array element thatreceives power directly from the transmitteror is connected directly to the receiver.

drive pin. A pin located to one side of center ona pnonograph turntable, sometimes used toprevent the record from slipping during re-cording or playback.

driver. The amplifier stage preceding the high -power output stage in a transmitter. It deliverspower as well as voltage for excitation of theoutput stage.

drop. The voltage developed across a resistor dueto current flow through the resistor.

dropping resistor. A resistor used to decrease thevoltage in a circuit.

drop -out current. That value to which the currentthrough a relay coil must be reduced beforethe armature will be released.

drum speed. The number of scanning lines perminute in a facsimile system.

drum switch. A series of contacts on a rotatingdrum that make contact with lingers fastenedto an insulated support, Used for complex cir-cuit changes.

dry battery. A group of dry cells connected invarious series, parallel, or series -parallel ar-rangements to get desired voltage and currentvalues.

dry cell. A type of primary cell in which the elec-trolyte is in the form of a paste rather than aliquid.

25

dry -disc rectifier. Dry contact rectifier. A rectifierconsisting of discs of metal and other materialin contact under pressure, such as a copper -oxide rectifier or a selenium rectifier.

dry electrolytic condenser. An electrolytic con-denser in which the electrolyte is a paste ratherthan a liquid, to permit using the condenserin any position without danger of leakage ofthe electrolyte.

dual capacitor. Two capacitors in a single hous-ing.

dual -diversify receiver. A radio receiver designedto receive signals from two different receivingantennas and use whichever signal is thestronger at any instant, in order to offsetfading.

dub. To make a copy of a sound recording by aprocess of re-recording.

duct. An atmospheric phenomenon consisting oftwo layers between which electromagneticwaves are channeled and, as a result, reflectedtoward the earth at a greater range thannormal.

dummy antenna. A resistor or other device thatduplicates the electrical characteristics of atransmitting antenna without radiating radiowaves. Used for testing and adjusting trans-mitters.

dummy load. A dissipative but essentially non -radiating device having the impedance charac-teristics of an antenna or transmission line.

duodiode. A vacuum tube having two diodes inthe same envelope.

duodiode-pentode. A vacuum tube having twodiodes and a pentode in the same envelope.Also called double -diode pentode.

duodiode-triode. A vacuum tube having diodesand a triode in the same envelope. Also calledduplex -diode triode.

duotriode. A vacuum tube having two triodes inthe same envelope. Also called double triode.

duplex operation. Simultaneous transmission andreception of radio signals.

duralumin. An alloy of aluminum comparable instrength and hardness to soft steel.

duty factor. The product of the pulse durationand the pulse repetition rate. It represents thetime in operation per second.

dynamic characteristic. A graph showing the op-erating conditions for a tube.

dynamic loudspeaker. A loudspeaker in which thediaphragm or cone is attached to a small coilthat is mounted so that it can move withina constant magnetic field. Audio frequencycurrents flowing through this coil produce avarying field that interacts with the fixed field,causing the coil to move in and out, therebycausing the cone to reproduce sound waves.

dynamic microphone. A microphone having a mov-ing coil mechanism similar to that in a dynamicloudspeaker. Sound waves move the diaphragm,causing the attached voice coil to move in andout of a fixed magnetic field produced by apermanent magnet. .An audio output voltageis thus induced in the moving coil.

dynamic noise suppressor. Circuit for audio ampli-fiers. especially those for record players. Theoutput at both ends of the frequency responseis cut off until the signal level at these frequen-cies exceeds the threshold level, so as to blocklow or high frequency noises.

dynamo. An electric motor or generator.

dynamotor. A rotating device acting both asmotor and generator, used to change a de volt-age to an ac voltage or to a higher dc voltage.

dynatron. A tube circuit arranged so that sec-ondary emission from the plate causes platecurrent to decrease as plate voltage is in-creased.

dynatron oscillator. An oscillator in which energyis delivered to a tank circuit because the tubeis made to have a negativ.e resistance charac-teristic.

dyne. The cgs unit of physical force. A dyne isequal to 1/980th gram.

dyne per square centimeter. The unit of soundpressure. The term "bar" was formerly usedto mean a sound pressure of one dyne persquare centimeter, but the term is beingdropped in acoustics.

dynode. An intermediate electrode between thecathode and plate of an electron -multipliertube. The dynode emits many secondary elec-trons for each incident electron striking it.

Eeccentric groove. A blank endless groove provided

on most phonograph records, whose center isother than that of the record. It actuates thetripping mechanism of an automatic recordchanger after the record has been played.

eccentric spiral. The blank spiral groove leadingfrom the end of the recorded part of a phono-graph record to the eccentric groove.

echo. A signal that has been reflected at one ormore points in the transmission medium, sothat it is received separately from the maintransmission. A sound wave heard after re-flection from one or more surfaces. Ghost.

echo area. The effective cross-sectional area of aradar target, resulting from scattering of thereflected beam.

echo chamber. A reverberant room used to addhollow effects and echoes to radio programs.

eddy current. Current induced in conductingmaterials by varying magnetic fields in such away that power is dissipated within the con-ductor in the form of heat.

Edison base. The standard screw base used forordinaty electrid light bulbs in the UnitedStates.

Edison cell. A storage battery using nickel andiron plates and an alkali electrolyte.

effective antenna length. The length which, whenmultiplied by the current at the point of maxi-mum current, will give the same product asthe length and uniform current of an elemen-tary dipole antenna at the same location, andgive the same radio field intensity in the direc-tion of maximum radiation.

effective current. The value of alternating currentthat will cause the same heating effect as agiven value of direct current. Also called therms current.

effective height. An antenna rating, equal to theheight of a perfect antenna giving the samefield strength.

effective resistance. In an ac circuit, the averagepower dissipated divided by the square of theeffective current.

effective radiated power. The power fed into theantenna multiplied by the antenna power gain.

26

effective value. The rms value of an alternatingcycle of current, voltage, or power. -

efficiency. The ratio of energy output to energyinput, usually expressed as a percentage.

elasticity. The ability of a substance to returnto shape after being stretched or otherwisedeformed.

E layer. An ionized layer in the atmosphere, ca-pable of reflecting or bending radio waves backto earth. The E region extends between about55 and 85 miles above the earth's surface.

electralloy. A soft iron alloy used for radiochassis construction.

electret. A dielectric that retains a charge afterthe charging field is removed, much as a per-manent magnet retains magnetism.

electrical angle. A phase angle expressed in de-grees.

electrical bandspread. Tuning by means of agang of low -capacity condensers connected inparallel with the main tuning gang of a short-wave receiver. After tuning to the desired bandwith the main gang, it is possible to "spreadout" that band over the complete rotation ofthe bandspread dial because the small capaci-tances give a smaller frequency change perdegree of rotation.

electrical center. The point approximately mid-way between the ends of an inductor or resistorthat divides it into two equal electrical values,as to voltage, resistance, inductance, or num-ber of turns.

electrical inertia. Inductance; opposition tochange in current flow.

electrical interference. Interference caused by theoperation of electrical apparatus other thanradio stations. Also called man-made inter-ference.

electrical transcription. A recording made ex-pressly for broadcast purposes.

electric eye. A cathode-ray tuning -indicator tubeused in some radio receiving sets. It consistsof a fluorescent screen with a dark sector thatvaries in direct proportion to the strength ofthe incoming signal. Also, a popular name fora photoelectric cell.

electric field. A region or space traversed by elec-tric lines of force.

electricity. A fundamental quantity in naturecharacterized by the fact that it gives rise to afield of force possessing potential energy, andthat when moving in a stream (electric cur-rent) it gives rise to a magnetic field withwhich kinetic energy is associated.

electric lines of force. Imaginary lines used todesignate the direction and amount of forceproduced by an electric charge.

electric organ. A musical instrument using elec-trical devices instead of wind to produce tonessimilar to those of a pipe organ.

electro-acoustic. Pertaining to a device whosefunctions involve both electric current andsound -frequency pressures.

electrochemical recording. Recording by means ofa chemical reaction brought about by the pas-sage of signal -controlled current through thesensitized portion of the record sheet of afacsimile receiver.

electrode. An essential part inside a vacuumtube, such as the cathode, the various grids,and the plate. Also, the plates of a primarycell, secondary cell, or electrolytic condenser,or the carbons of an arc.

electrode current. The current passing to or froman electrode, particularly that through thespace inside a vacuum tube.

electrode dissipation. Power dissipated as heat bya vacuum -tube electrode as a result of electronand/or ion bombardment.

electrode voltage. The voltage applied betweenanother electrode and the cathode in a vacuumtube.

electrodynamic loudspeaker. A dynamic loudspeak-er in which the magnetic field is produced byan electromagnet.

electrodynamometer. An instrument having twocoils, arranged so the interaction of their fieldsactuates an indicator, used to measure dc andlow -frequency ac currents.

electrolysis. Corrosion caused by a current flow-ing in and out of the surface of a conductorwhen resistance develops in a joint in the nor-mal current path, or conductivity develops inadjoining insulation. Chemical decompositionby the action of an electric current.

electrolyte. The chemical liquid or paste usedbetween the electrodes of a dry cell, storagebattery, or electrolytic condenser.

electrolytic cell. A cell containing two electrodes,used to dissociate an electrolyte into its com-ponents.

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Electrolytic Condenser

electrolytic condenser. A fixed condenser contain-ing a liquid or paste electrolyte, in which thedielectric is a thin film formed on the surfaceof one electrode.

electromagnet. A core of magnetic material, sur-rounded by a coil, and magnetized by a cur-rent flowing through the coil.

electromagnetic deflection. The process of bendingor altering the path of an electron stream bymeans of a magnetic field created by the pas-sage of current through coils.

electromagnetic field. The combined electric andmagnetic fields produced by the flow of elec-trons through a wire or coil.

electromagnetic induction. The action that causesa voltage to be induced in a conductor whenthe number of magnetic lines of force linkingwith the conductor is changed.

electromagnetic units (emu). A system of electricalunits of measurement, derived from basic cgsunits, assuming the magnetic permeability ofair as 1.

electromagnetic wave. A wave in which there areboth electric and magnetic fields, at rightangles to each other. Electromagnetic wavesare known as radio waves, infra -red rays,light, x-rays, etc., depending on the frequency.

electromagnetism. Magnetic effects produced byelectric currents.

electromechanical. Pertaining to a combination ofmechanical and electric forces.

27

electromechanical recording. Facsimile recordingby means of a signal -actuated mechanical de-vice.

The electron current arriving at the anode isthe sum of the individual secondary emissioncurrents and the initial cathode current.

electromotive force (emf). The force causing mo-tion of electrons. Voltage.

electron. The elementary particle of negativeelectricity. Some electrons are closely asso-ciated with atoms of matter; others, calledfree electrons, move readily between atoms un-der the influence of electric or magnetic fields,or are emitted under the influence of heat. Themovement of electrons through a conductorconstitutes an electric current.

electron beam. A stream of electrons, such as ina cathode-ray tube or in a klystron.

electron -coupled oscillator. An oscillator circuitusing a screen -grid or pentode tube in whichthe oscillator transfers energy to the outputcircuit through the stream of electrons fromthe cathode, instead of through direct coupling.

electron coupling. A method of coupling in whichan electron stream transfers energy from theanode grid of the oscillator to the plate loadcircuit.

electron drift. The actual movement of electronswhen current flows.

electron emission. The release of electrons fromthe surface of a material into surroundingspace due to heat, light, high voltage, orother causes.

electron focus. Use of an electrostatic or electro-magnetic field to converge the electron beamin a cathode-ray tube to a small spot on thescreen.

electron gun. The part of a cathode-ray tube thatincludes the electron -emitting cathode and theassociated parts that concentrate and controlthe stream of electrons.

electronic control. The control of a machine ordevice by apparatus using electron tubes.

electronic key. A circuit that automatically pro-duces dots and dashes of uniform size.

electronic keying. A method of telegraphic keyingin which the keyed stage is controlled by atube that in turn is made to function by amanually operated key.

electronic lens. An arrangement of electrodesand/or magnetic deflecting and focusing coilsused to control the direction and size of abeam of electrons.

electronic optics. That branch of electronics deal-ing with the control of the movements of elec-trons by the application of electrostatic andelectromagnetic forces.

electronics. The branch of science relating to theconduction of electricity through gases or ina vacuum.

electronic television. A television system in whichthe scene to be transmitted is scanned and re-constructed by electron beams in cathode-raytubes, rather than by mechanical means.

electron microscope. A device that directs a beam, of electrons on the object being examined.

magnifies the resulting shadow, and makesthis shadow visible on a fluorescent screen orrecords it on photographic film.

electron -multiplier tube. A vacuum tube designedso that the initial electron current produced bya thermionic or light-sensitive cathode causessecondary emission from a number of dynodes.Each time a dynode is struck by an electronstream, the secondary electrons combine withthe electron stream, which in turn producesmore secondary emission from the next dynode.

Courtesy GEElectron Ray Tuning Indicator

electron -ray tuning indicator. A vacuum tube witha fluorescent screen, used in receivers to in-dicate when a station is tuned in accurately.

electron tube. Any partly evacuated, completelyevacuated, or gas -filled tube used to controlthe flow of electrons in a circuit. Vacuum tubes,phototubes, mercury-vapor rectifier tubes, andcathode-ray tubes are all electron tubes.

electron volt. The energy possessed by an electronthat has undergone a change of potential ofone volt.

electroplating. A process for applying a coatingof metal to a conductive surface by means ofan electric current.

electroscope. An instrument for detecting staticcharges of electricity.

electrostatic. Pertaining to static electricity,charges, and potential differences.

electrostatic charge. An electric charge in a ca-pacitor or on the surface of an insulated object.

electrostatic coupling. The coupling of two cir-cuits by a capacity, so that one circuit influ-ences the other through condenser charges anddischarges.

electrostatic deflection. The process of bendingthe electron stream in a cathode-ray tube bythe use of an electrostatic field.

electrostatic field. See electric field.

electrostatic focusing. Focusing of an electronbeam in a cathode-ray tube by the action ofan electric field.

electrostatic induction. Accumulation of an in-duced charge on a conductor as a result ofplacing a charge in the vicinity. If a negativecharge is brought near an uncharged conduc-tor, electrons in the conductor will recede, pro-ducing an induced positive charge.

electrostatic scanning. The deflection of an elec-tron beam to form a raster by means of anelectrostatic field.

electrostatic shield. A grounded piece of metal ora grille consisting of vertical or horizontalwires but not both, used to prevent an electricfield from transferring energy. See Faradayshield.

electrostatic units (esu). A system of electricalunits of measurement, derived from basic cgsunits, assuming the dielectric coefficient of airas 1.

electrostatic voltmeter. A voltmeter that operateson the principle that two like charged bodieswill repel each other. Such a voltmeter has twoplates opposite each other, one free to move.

28

As the voltage applied to the plates is in-creased, the movement increases, and a pointerconnected to the movable plate indicates thevoltage applied.

electrothermal recording. The type of electro-chemical facsimile recording in which thechemical change is produced principally byheat.

element. One of the known basic forms of matterthat make up the universe. Also the componentparts of a device; thus, the cathode, grid, andplate would be called the elements of a triodevacuum tube.

elemental area. In television and facsimile, asquare segment of a scanning line, the lengthof which is equal to the nominal line width.

eliminator. A device that replaces batteries as asource of current and voltage.

elliptically polarized wave. A wave in which thedirection of displacement rotates around anaxis, and the magnitude of displacement variesas the radius of an ellipse.

embossed recording. A method of sound recordingon discs or film by mechanical pressure. Modu-lation grooves are formed by pressure dis-placement of the recording base material, in-stead of by cutting out the material.

emission. Giving off of electrons. Also, the radia-tion of energy into space as from yan antenna.

emission characteristic. A relation, usually shownby a graph, between electron emission andsome factor controlling the emission, such asthe temperature, voltage, or current of thefilament or heater.

emission efficiency. The amount of electron emis-sion from a cathode per watt of heatingpower.

emission types. A classification of kinds of radiotransmission, adopted by international agree-ment, in which the type of modulation, typeof transmission, and supplementary character-istics are represented by symbols. For exam-ple, A5 represents amplitude modulation, tele-vision; F3 represents frequency modulation,telephony (broadcasting): P3e represents pulsemodulation, telephony, width modulated.

emission velocity. The initial velocity with whichelectrons emerge from a cathode surface.

emitron. Term applied to one British version ofa television camera tube.

emphasizer. A series of components connected ina circuit to increase signal amplitude at cer-tain audio frequencies.

empirical. Based on experience or observation.

enameled wire. Wire coated with an insulatinglayer of baked enamel.

end effect. The effect of capacitance at the endsof an antenna. Also, the effect of inductanceat the end of a coil. .

end -fire antenna array. An array in which theelements are side by side, parallel, and alllying in the same horizontal plane.

energy. Ability to do work.

envelope. Two curves, one drawn through thenegative, and the other through the positivepeaks of a graph of the wave form of an rfsignal. Also the glass or metal housing of atube.

E plane. The plane of an antenna in which theelectric field lies, perpendicular to the Hplane.

equalizer. A part or circuit used to produce a flatelectrical or acoustical frequency response overa desired frequency range, or for changing theresponse to satisfy particular requirements.

equalizing pulses. A series of pulses' occurring attwice the horizontal frequency, placed beforeand after each vertical sync pulse, and usedto maintain proper horizontal sweep controlin a television system.

equation. A mathematical statement that twonumbers, quantities, or expressions are equal.Examples: P = El; 72 49; (a + b)2 -= az

2ab b2. A formula is an equation be-cause it involves equality, but an equation isa formula only when it expresses a scientificfact, law, or principle.

equipotential line. An imaginary line In spacealong which all points have the same poten-tial.

equisignal radio -range beacon. A radio -beacon sta-tion that transmits two distinctive signals,these being received with equal intensity onlyalong certain paths that constitute the routefor airplanes.

equisignal sector. The on -course region in whichthe two different signals from an equisignalradio -range beacon are received with equalintensity.

equivalent emit. An arrangement of resistors,coils, and condensers to simulate or electricallyreplace a more complicated circuit, to permitanalysis.

equivalent loudness level. The intensity level indecibels of a 1000 -cycle pure tone equivalent inloudness to the sound under consideration.

equivalent plate voltage. A theoretical voltage inthe plate circuit equal to the ac grid voltagemultiplied by the amplification factor of thetube.

equivalent resistance. A lumped or concentratedresistance that would cause the same loss as'smaller resistance values distributed through-out an entire part or circuit. Used chiefly forconvenience in computations or for determin-ing circuit actions.

E region. The region of the ionosphere betweenabout 55 and 100 miles above the earth's sur-face.

erg. The basic unit of work in the cgs system.l'he work done by a force of one dyne actingthrough a distance of one centimeter.

escutcheon. The ornamental wood, metal, orplastic framework for a dial, tuning indicator,or other panel -mounted part in a receiver oramplifier.

ether. The medium that was once supposed tofill all space, and through which radio, heat,and light waves were supposed to travel.

E waves. Electric field waves.

excitation. Application of a signal to the input ofan amplifier stage, or application of signalpower to a transmitting antenna. Also, appli-cation of voltage to the field coils of a motoror generator, or to the field coil of an electro-dynamic loudspeaker.

excitation anode. Auxiliary starting electrode ofa mercury arc rectifier.

exciter. In a directional transmitting antennasystem, the part directly connected to thetransmitter. In a transmitter, the exciter is thecrystal oscillator or self-excited oscillator thatgenerates the carrier frequency. Also, the smallauxiliary generator used to provide field exci-tation for some large generators.

29

exciting current. The current that flows throughthe primary winding of a power transformerwhen there is no load connected to any sec-ondary winding.

expansion. Widening the volume range of anaudio -frequency signal so that weak passagesbecome weaker and loud passages becomelouder. Volume expansion.

exploring coil. A small coil used in measuring amagnetic field.

exponent. A number written at the right of andslightly above another number to indicate howmany times the number is to be multiplied byitself. The result is the power of the number.Examples: 54 means 5 X 5 x 5 X 5, and ispronounced "5 to the fourth power." The re-sult, 625, is the fourth power of 5. 12 means1 X 1. and is pronounced "1 squared" or"1 to the second power." A negative exponentmeans to find the reciprocal of the numberwith a positive exponent. Example:

b- s = 1

A fractional exponent indicates the root of aquantity. Example:

1 1 5

XF means Nix; xr means '/x; xs means -syx2.exponential horn. A loudspeaker horn whose cross-

sectional area varies exponentially with itslength.

extended cut-off. See remote cut-off tube.

extinction potential. The lowest value to which theplate voltage of a gaseous triode can be re-duced, without stopping the flow of plate cur-rent.

extraordinary wave. One of two components intowhich a radio wave is split in the ionosphereby the earth's magnetic field. Sometimes calledthe X wave. The other component is the or-dinary wave.

Ffacsimile. The process of transmitting and re-

producing photographs, drawings, handwrit-ing, sketches, and printed matter of any kindby means of a radio or wire communicationsystem. "Type A facsimile" is a system inwhich images are built up of lines of dots ofconstant intensity. "Type B facsimile" (tele-photography, photoradio, etc.) is a system inwhich images are built up of lines or dots ofvarying intensity.

facsimile receiver. The apparatus that trans-lates the signal from the facsimile communi-cation channel into a facsimile record of thesubject copy.

facsimile recorder. The part of a facsimile re-ceiver in which the picture signal is registeredupon a paper record sheet.

facsimile transmission. The transmission of signalwaves produced by scanning fixed graphicmaterial.

facsimile transmitter. The apparatus used totranslate pictures and other subject copy intosignals to be transmitted.

factor. If two or more numbers are multipliedtogether, each of them, or the product of anycombination of them, is a factor of the product.Example: 2, x, y, 2x, 2y, and xy are all factorsof 2xy.

fade. To change gradually. A program is fadedin by making it gradually louder or brighter,and is faded out by diminishing its voltme orbrilliance graddally to zero.

fadeout. Intentional, gradual disappearance ofa movie or television scene prior to showinga different scene. Also, the failure of radiowaves to arrive at a location because of mag-netic storms or atmospheric disturbances.

fader. A device for electrically fading a programin or out. Also, a control that gradually re-duces the volume of one signal while graduallyincreasing the volume of another signal.

fading. A variation in the intensity of receivedsignals because of changes in atmospheric con-ditions along the path between the transmitterand the receiver.

Fahnestock clip. A spring -type terminal to whicha temporary connection can readily be made.

Fahrenheit (F). The temperature -measuring sys-tem generally used in the United States, inwhich 32 degrees is the freezing point and 212degrees is the boiling point of water at sealevel.

fan antenna. An antenna in which the elementsare in a vertical plane and spread out fan -wise from a common junction.

fan marker beacon. A transmitter having a radia-tion pattern in the shape of a fan, extendingupward and at right angles to an airway beaconcourse to indicate position along the course.

farad. The basic unit of capacity. A condenseris said to have a capacity of 1 farad when achange of / volt per second across it producesa current of 1 ampere. A microfarad equalsone millionth of a farad. A micromicrofaradequals one millionth of a microfarad.

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Facsimile Receiver

Faraday shield. A network of parallel wires allinterconnected at the same end like a comb, toprovide electrostatic shielding. The end thatconnects to all conductors is grounded, and theentire assembly is placed between two coils toeliminate stray capacity, or around a loopaerial to eliminate electrostatic pickup of sig-nals. A Faraday screen.

Federal Communications Commission (FCC). Aboard of commissioners appointed by the Presi-dent, with power to regulate all U. S. commu-nication systems, including radio, television,telegraph, cable, and telephone.

feed. To supply electric energy to one part orstage from another part or stage.

feedback. The return of a fraction of the elec-trical or the acoustic output to the input. Whenthe fed -back signal is in phase with the inputsignal, positive feedback or regeneration ex -

30

ists and increases the amplification. When thefed -back signal is out of phase with the inputsignal, negative feedback or degeneration ex-ists and decreases the amplification.

feedback cutter. In sound recording, a cutter inwhich a voltage generated by movement of thecutting stylus is fed back into the amplifiersystem, for theurpose of reducing distortionand stabilizing frpequency characteristics.

feeder. A wire or set of wires supplying energyfrom a source to a load.

ferromagnetic. Magnetic in a high degree, likeiron.

fiber. A hard, tough material made of woodpulp, compressed into sheets, rods, or tubes,and used in radio for insulating and supportingpurposes.

fidelity. The faithfulness with which part or allof an electrical system delivers an exact re-production of the input signal.

field. In black -and -white television, the areacovered during one vertical sweep of thescene; consequently, in double -interlacedscanning, the field is one-half the area of thescene. In color television, scanning throughthe picture area once in the chosen scanningpattern and in one of the primary colors; con-sequently, in 2 -to -1 line -interlaced scanning,the scanning of alternate lines once in a singlecolor. Also see color field. Also, a general termdescribing the space surrounding an electri-cally charged object or magnet. See electricfield and magnetic field.

field coil. In an electrodynamic loudspeaker,electric motor, or generator, the coil or coilsthat produce the magnetic field.

field frequency. In television systems using in-terlaced scanning, the number of times persecond the frame area is scanned by a down-ward sweep of the electron beam.

field gain. The ratio of the field intensity of amulti -element antenna to that of a simplehalf -wave antenna fed with the same power.

field intensity. The effective (rms) value of theelectric or magnetic field produced at a pointby radio waves from a particular station. It isusually expressed as electric field intensity inmicrovolts per meter or millivolts per meter.Also, the amount of magnetic flux produced byan electromagnet or permanent magnet.

field of view. The area included in a televisedimage as "seen" by the camera.

field period. In television, the length of timerequired to scan one field, equal to 1 dividedby the field frequency.

field pole. The structure of magnetic materialon which a field coil is wound in a motor, gen-erator, loudspeaker, etc.

field repetition rate. See field frequency.field rheostat. A variable resistance used to regu-

late the current flowing through the field coilsof a motor or generator.

field sequential. In color television, an arrange-ment in which an entire field is scanned in oneprimary color before it is scanned in anothercolor.

field strength. See field intensity.figure of merit. A property or characteristic ofa tube, coil, or other electronic device that

makes it suitable for a particular application.filament. The resistance wire through which cur-

rent is sent in a vacuum tube to produce theheat required for electron emission. When elec-

tron emission is from the surface of the fila-ment wire itself, the filament also serves asthe cathode.

filament circuit. The complete circuit throughwhich current flows from the filament voltagesource to the filaments of radio tubes.

filament current. The current supplied to the fila-ment of a vacuum tube for heating purposes.

filament emission. The process by which electronsare given off from a heated filament in a vac-uum tube.

filament rheostat. A variable resistance used tolimit the flow of current through the filamentsof vacuum tubes.

filament saturation. See temperature saturation.filament voltage. The voltage that must be ap-

plied to the filament terminals of a vacuumtube in order to send the rated value of cur-rent through the filament.

filament winding. A separate secondary windingprovided on a transformer for use as a filamentvoltage source.

film scanning. The process of converting moviefilm into electrical signals that can be trans-mitted by a television system.

filter. A selective network designed to pass sig-nals within a certain range of frequencies whilereducing considerably the amplitudes of sig-nals at undesired frequencies. A low-pass filterpasses all frequencies below its cut-off value.A high-pass filter passes all frequencies aboveits cut-off value. A band-pass filter passes allfrequencies between its two cut-off values. Aband -elimination filter passes frequencies out-side its two cut-off values, eliminating fre-quencies between. A filter consists of somecombination of resistors, coils, and condensers,sometimes also with a crystal. Also, a sub-stance that absorbs or blocks certain colors oflight while allowing others to pass.

filter choke. A coil used in a filter system.filter condenser. A condenser used in a filter sys-

tem.

fine tuning control. A control on the receiver thatpermits varying the frequency of the local os-cillator over a small range to compensate fordrift and permit accurate adjustment to a sta-tion's carrier frequency.

fins. Radial sheets or discs of metal attached toa power tube or other component for dissipat-ing heat.

firing. The process of gas ionization and thestart of current flow in gas or vapor -filledtubes.

firing point. The voltage at which the gas orvapor in a tube ionizes and current begins toflow.

firing potential. See firing point.first audio stage. The first stage in the audio

amplifier of a receiver to which audio signalsare fed.

first detector. The stage in a superheterodynereceiver in which the incoming modulated rfsignal and the rf signal from the local oscilla-tor are combined to produce the i-f signal.

fishbone antenna. A directional antenna consist-ing of a number of doublets attached to a trans-mission line, with all doublets making thesame angle with the line, to form a herring-bone pattern.

fishpaper. A specially treated fiber paper used toinsulate transformer windings.

31

do voltage proportional to the frequency differ-ence between the carrier frequency and its as-signed frequency.

frequency distortion. A type of distortion thatoccurs when a circuit or device amplifies ortransmits unequally the different frequenciesit is handling.

frequency divider. A device delivering outputvoltage at a frequency that is a fraction of theinput frequency. A flip-flop circuit.

frequency -division multiplex. A system of sendingtwo or more signals on one carrier by causingeach modulating signal to modulate differentsub -carriers, all of which in turn modulatethe main carrier.

frequency doubler. A circuit arranged so that thefrequency of its output is twice that of its in-put. Usually it is a class C amplifier adjustedso that the plate circuit will have strong har-monics of the input signal, with the plate tankcircuit tuned to the second harmonic of theinput. It may also be a full -wave rectifier feed-ing a tank circuit tuned to the second har-monic of the input.

frequency drift. A slow change in the frequencyof an oscillator or transmitter, usually due totemperature changes in oscillator circuit parts.

frequency meter. An instrument for measuringfrequency. A wavemeter.

frequency modulation. A system of radio broad-casting in which the amount of deviation infrequency above and below the resting fre-quency is at each instant proportional to theamplitude of the sound wave being transmitted,and the number of complete deviations per sec-ond above and below the resting frequency isequal to the frequency of the sound wave beingtransmitted.

frequency monitor. An instrument that indicatesthe amount of frequency deviation.

frequency multiplier. A stage or section used toincrease the frequency of a signal, such as adoubler, tripler, etc.

frequency, natural. The resonant frequency of atank circuit.

frequency range. A frequency band, especiallyone including the frequencies at which a sys-tem is able to transmit, receive, attenuate, oramplify power.

frequency record. A phonograph record used as asource of signals for testing audio equipment.Various known frequencies throughout theaudio frequency range are recorded at fixedamplitudes on this record.

frequency regulator. A device that maintains thefrequency of a signal source at a predeter-mined value.

frequency response. The manner in which a cir-cuit or device handles the frequencies fallingwithin its operating range.

frequency response curve. A graph showing thefrequency response of a radio part, circuit, orsystem.

frequency separator. The television receiver cir-cuit that separates the horizontal synchronizingpulses from the vertical synchronizing pulses.

frequency shift. A change in the frequency of anoscillator or transmitter.

frequency -shift transmission. A system of codetransmission that shifts the carrier frequencyback and forth between two distinct frequen-cies to designate mark and space, instead ofkeying the carrier on and,off.

frequency stability. The ability of a transmitter,signal generator, or other signal source tomaintain a given frequency. Usually expressedas a percentage of deviation within which thefrequency is maintained.

frequency stabilization. The process of controllingthe frequency so that it does not differ morethan a prescribed amount from that of a refer-ence source.

frequency standard. A highly stable, accurate,signal source which generates a frequency towhich, or to the harmonics of which, otherfrequencies can be compared.

frequency swing. In frequency modulation, thedeparture of the carrier frequency from theresting frequency.

frequency tolerance. The maximum permissibleamount of variation in either direction fromthe assigned carrier frequency.

frequency tripler. A device delivering outputvoltage at a frequency three times the inputfrequency.

frictional loss. Energy expended in overcomingfriction between moving parts.

friction tape. Cotton tape impregnated with asticky moisture -repellent compound, usedchiefly to hold rubber -tape insulation in place.

fringe howl. A squeal or howl heard when somecircuit in a receiver or amplifier is on theverge of oscillation.

front porch. In a television signal, the portionof the blanking pedestal immediately preced-ing a synchronizing pulse, by which the sig-nal is held at the black level to prevent pic-ture information from interfering with syn-chronization.

front -to -back ratio. In a multi -element directionalantenna, the ratio between the signal radiatedor received in the desired front direction andthe signal radiated or received in the oppositeor rear direction. Also called front -to -rearratio. Also, in non -tube rectifiers such asselenium rectifiers or germanium crystals, theratio of the current in the desired direction tothat passed in the undesired direction.

full -wave rectifier. A radio tube or other devicethat rectifies an alternating current in such away that both halves of each input ac cycle ap-pear in the pulsating rectified output. A full -wave rectifier tube contains two separate diodesections, one passing current during one al-ternation, and the other passing current dur-ing the opposite half -cycle.

fundamental frequency. 'The lowest frequencycomponent in a complex signal having har-monics. The lowest or natural resonant fre-quency of a part or circuit.

fundamental wavelength. The wavelength corre-sponding to the fundamental frequency.

fuse. A protective device consisting of a shortpiece of wire or strip of metal that melts andbreaks when the current through it exceeds therated value of the fuse. Fuses are inserted toopen a circuit automatically in case of seriousoverload, thereby preventing damage to parts.

fuse block. An insulating base on which aremounted fuse clips or other contacts for hold-ing fuses.

fuse clip. A spring contact for holding a fuse inposition and providing a connection.

fuse link. The metal portion inside a fuse thatmelts at the rated current value.

fuse wire. Wire made from an alloy that meltsat a relatively low temperature.

34

Ggage. Alternate selling of gauge.gain. In an amplifier stage or system, the ratio

of output to input, sometimes expressed indecibels.

gain control. A control connected so that it canchange the over-all gain of an amplifier orsystem. A volume control or contrast control.

gain of an antenna. A rating expressing howmuch better one transmitting or receiving an-tenna is than another. For constant transmittedpower level, the measured gain is the ratio ofthe signal powers produced at the input ter-minals of a receiver by the antennas undercomparison.

galena. Lead sulphide, a shiny, bluish -graymineral once widely used as the crystal incrystal detectors.

galvanometer. A current -indicating meter, usual-ly having a scale indicating relative deflectionor degrees of deflection, from which theamount of current can be calculated. Whenthe meter has a current scale indicating milli-amperes or amperes, it is called a milliammeteror ammeter.

gamma. The ratio of the contrast of any twoelements of the picture to the original contrastof these same elements in the scene being tele-vised.

gamma ray. An electromagnetic radiation, simi-lar to x-rays but of shorter wavelength.

gang. A number of similar pieces of apparatusmounted so they can be simultaneously ad-justed by a single control shaft.

gang switch. Two or more rotary switchesmounted on the same shaft and operated by asingle control.

gang tuning condenser. Two or more variable tun-ing condensers mounted on the same shaft andoperated by a single control.

Gang TuningCondenser

gap. In a device in which a ferromagnetic sub-stance provides most of the path for magneticflux, the gap is that portion of the magneticcircuit in which there is no ferromagnetic ma-terial. Also the space between the surfaces oftwo electrodes.

gap arrester. An antenna lightning arrester inwhich there is an air gap between two metalpoints that in turn are connected to the an-tenna and ground. The gap arcs over when theantenna is struck by lightning, grounding thecharge.

gas current. A current consisting of positive ionsproduced by gas ionization in a tube.

gaseous conduction. The conduction of electricitythrough a gas due to ionization of the gas by

collision of electrons with gas molecules.gaseous tube. An electronic tube into which a

small amount of gas or vapor is admitted afterthe tube has been evacuated. Ionization of thegas molecules during operation of the tubegives greatly increased current flow.

gas focusing. Focusing of the electron beam in acathode ray tube by the action of ionized gas.

gasket. A ring or washer used for packing orinsulating.

gas magnification. The increased electron flow ina gas -filled photocell due to ionization of gas.

gasoline -driven generator. An ac or de generatoroperated by a gasoline engine.

gassing. The production of gases when a currentis passed through a chemical solution. Specifi-cally, the liberal production of gas in a storagebattery when charging is continued after thebattery is completely charged.

gassy tube. An imperfectly evacuated tube, onein which a small amount of gas accidentallyremains. A "soft" tube.

gas tube. A vacuum tube in which gas or vaporis enclosed in order to substantially affect theelectrical characteristics of the tube.

mating. The process of selecting those portionsof a wave that exist during one or more timeintervals or which have magnitudes betweenselected limits.

gauge. A standard of measurement or a devicefor measuring.

gauss. The unit of flux density, equal to onemagnetic line of force per square centimeter.The term gauss has also been used as a unitof magnetic field intensity, equal to one gilbertper centimeter.

Geiger counter. Any of several devices for de-tecting and measuring radiation, as theGeiger -Mueller counter.

Geiger -Mueller counter. A device for measuringradiation, containing a gas -filled tube consist-ing of a metallic cylindrical sheath having aslender wire running axially through its cen-ter. Radiation such as from x-rays, gammarays, beta rays, and alpha rays, traversing thegas causes ionization of the gas thus permittinga pulse, to actuate an amplifying or countingcircuit.

Geissler tube. A long gaseous tube that gives offcolored light when a suitable voltage is ap-plied to the electrodes, which are at oppositeends of the tube.

genemotor. A small motor -generator set, gen-erally employed for plate voltage supply inmobile radio installations.

general number. A letter or symbol used for rep-resenting quantities. Thus, R is a general num-ber (sometimes called a literal number) usedto represent resistance.

generator. A machine that converts mechanicalenergy into electrical energy. It usually con-sists of a number of conductors mounted onan armature rotated in a magnetic field pro-duced by field coils. A series generator has thearmature, field, and load all in series. A shuntgenerator has the armature, field, and load allin parallel. A compound generator has twofields, one in series with the armature and theother in parallel with the armature. Also, adevice, such as an oscillator, that develops anac voltage at a desired frequency when ener-gized with do or low -frequency ac power.

geometric distortion. Non-linear aberrations in aTV picture's raster, such as keystoning.

35

geometric mean. The square root of the productof two quantities.

geometry. The branch of mathematics that dealswith the relations and measurements of solids,surfaces, lines, and angles.

germanium. A metallic element used as a detec-tor because it has unidirectional conductivity.

german silver. An alloy of brass and nickel.getter. An alkali metal introduced into a vacuum

tube during manufacture and vaporized afterthe tube has been evacuated, to absorb anygases that may have been left by the vacuumpump. The silvery deposit on the inside of theglass envelope of a tube, usually near the tubebase, is the result of getter evaporation.

Courtesy BelmontTelevision Ghost

ghost. In. television, an undesired duplicateimage appearing a fraction of an inch to oneside of the desired image, due to reception ofa reflected signal along with the signal com-ing directly from the television station.

gilbert. The unit of magnetomotive force. Onegilbert is equal to .796 ampere -turn.

Gill -Morrell oscillator. A retarding field oscillatorin which the frequency of oscillation is de-pendent not only on electron transit time with-in the tube, but also on associated circuitparts values.

gimmick. A simple capacitor formed by twistingtwo wires together. Also, a piece of insulatedwire, one end of which is connected to theantenna terminal of an antenna transformer,the other end being left unconnected. It iswound around the secondary to provide capac-ity coupling.

glide path. The path an airplane is to followwhen using an instrument landing system. Itis formed in space by two intersecting fieldpatterns radiated in such a way that the glidepath is the equisignal zone.

glow discharge. A current flow through a gastube, at such a level that the space potentialnear the cathode exceeds the ionization poten-tial of the gas, causing a visible glow.

glow -discharge voltage regulator. A gas tube whoseresistance varies between about 5000 and 30,000ohms. depending on the amount of appliedvoltage; used to maintain a constant voltagesupply.

glow lamp. A gaseous tube having a glass en-velope through which a glow due to ionizationof the molecules of gas can be seen.

goniometer. An rf transformer used with a radiocompass or direction finder. It has two pri-

maries at right angles, each connected to aloop antenna, and coupled to a rotary second-ary. Rotating the secondary coil has the sameeffect as does rotating a loop antenna.

gradient. The rate of increase or decrease of avariable magnitude. Also, the curve represent-ing such a rate of change.

gram. The unit of weight in the metric system.One pound is equal to 453 grams.

gramophone. A phonograph (English term).

graph. A pictorial representation of the relationexisting between two or more quantities.

graphite. A soft form of carbon, used as a lubri-cant.

Grapjioline. A lubricant containing carbon, usedwhere conductivity must be maintained.

gray scale. A scale of brightness values.

Greenwich Mean Time (GMT). The time alongthe zero meridian of longitude which passesthrough Greenwich, England.

grid. An electrode mounted between the cathodeand the anode of a radio or electronic tubeto control the flow of electrons from cathodeto anode.

grid bias. The voltage used to make the controlgrid of a radio tube negative with respect tothe cathode. C bias.

grid bias cell. A bias cell used in the grid cir-cuit of a vacuum tube.

grid -cathode capacitance. The capacitance be-tween the grid and the cathode inside a vac-uum tube.

grid characteristic. The graph plotted with gridvoltage values as abscissas and grid currentvalues as ordinates.

grid circuit. The circuit connected between fhegrid and cathode of a tube. It forms the inputcircuit of the tube.

grid clip. A spring clip used to make an easilyremovable connection to the cap terminal lo-cated at the top of some radio tubes.

grid condenser. A small fixed condenser used' inconjunction with a resistor in the grid circuitof a vacuum tube for automatic biasing.

grid conductance. The ratio of the change in gridcurrent to the change in grid voltage producingit, under the condition of constant plate volt-age.

grid -controlled thyratron. A gaseous tube in whichthe grid determines when plate current startsto flow but not how much current will flqw.

grid current. The current passing to or from agrid through the space inside a vacuum tube.

grid detection. Detection taking place in the gridcircuit of a vacuum tube. Also called gridleak detection.

grid dip oscillator. An oscillator with a sensitivecurrent meter connected in its grid circuit.When the oscillator is coupled to a resonantcircuit, a sharp change in the meter readingindicates that power is being drawn from theoscillator and the two are in resonance.

grid emission. Emission of electrons or ions froma grid, usually due to the impact of electronsgoing from cathode to plate in the vacuumtube.

grid leak. A resistor of high ohmic value, son-nected between the control grid and the cath-ode in a grid -leak condenser detector circuit,for automatic biasing.

36

grid -leak condenser detector. A circuit in whichdetection occurs in the grid circuit of a tube,as the result of the diode action of the gridand cathode. The audio signals developedacross the grid resistor are amplified by thetube.

grid -leak defector. See grid -leak condenser de-tector.

grid limiter. A circuit in which the plate currentcannot increase appreciably with signal in-creases, because once the signal exceeds acritical value, grid current flows through a re-sistor in the grid circuit, thus producing anautomatic bias that opposes further signal in-creases.

grid modulation. Modulation produced by intro-duction of the modulating wave into a grid cir-cuit in which the carrier frequency wave ispresent.

grid neutralization. Neutralizing an amplifier byshifting part of the grid -cathode ac voltage180° and applying it to the plate -cathode cir-cuit through a neutralizing capacitor.

grid -plate capacitance. The capacitance betweenthe grid and the plate within a vacuum tube.

grid pulse modulation. Modulation produced in anamplifier or oscillator by application of one ormore modulating pulses to a grid circuit.

grid return. The lead or connection that providesa path for electrons from the grid circuit orC bias battery to the cathode.

grid suppressor. The resistor connected between. the control grid and the tuned portion of the

grid circuit of a radio -frequency amplifier toprevent oscillation.

grid swing. The total variation of grid voltagefrom positive peak to negative peak of the ap-plied signal.

grid voltage. Voltage between grid and cathode.It is the grid signal voltage, or the grid biasvoltage, or their combined voltage.

grille. An arrangement of wood or metal barsplaced across the front of the loudspeaker ina receiver for protective purposes and to en-hance the appearance of the cabinet.

grille cloth. A loosely woven cloth stretched be-hind the loudspeaker grille of a receiver tokeep dust and other foreign matter out of theloudspeaker, as well as to conceal the loud-speaker diaphragm. Sound waves travel un-impeded through this cloth.

grommet. A washer made of rubber or other in-sulating material used to prevent a wire orpart from touching the sides of a chassis hole.

groove. The track cut in a phonograph recordby the stylus during recording, or the trackin which a phonograph needle rides duringplayback.

groove velocity. The rate of motion of a phono-graph needle from side to side in the groove.

ground. The earth, to which a connection is madeby means of a buried conductor for radio pur-poses. Also, the chassis of a receiver when itserves as the return path for signal circuits.

ground absorption. The loss of power in trans-mission of radio waves due to dissipation inthe ground.

ground clamp. A metal strap or clamp used formaking a good electrical connection to aground rod or grounded pipe. The clamp hasa screw terminal or soldering lug to which the

ground wire of a receiver can readily be at-tached.

ground -controlled approach (GCA). The techniqueand/or apparatus for giving instructions to apilot for landing under the conditions of poorvisibility.

ground -controlled interception (GCI). Use of aradar display on the ground to locate enemyaircraft and guide intercepting aircraft tothem.

grounded. Connected to earth or to some con-ducting body that serves in place of the earth.

grounded -cathode amplifier. A vacuum tube ampli-fier with cathode at ground potential at theoperating frequency, with input applied be-tween control grid and ground, and the outputload connected between plate and ground. Thisis the "normal" amplifier connection for broad-cast -band frequencies.

grounded -grid amplifier. A vacuum tube amplifiercircuit in which the control grid is at groundpotential at the operating frequency, with in-put applied between cathode and ground, andoutput load connected between plate andground.

grounded -plate amplifier. A vacuum tube ampli-fier circuit in which the plate is at ground po-tential at the operating frequency, with inputapplied between control grid and ground, andthe output load connected between cathodeand ground. Also known as a cathode follower.

ground potential. The potential of the earth. Achassis, circuit, or terminal is at ground po-tential when it is electrically connected to theearth.

ground -reflected wave. The component of theground wave that is reflected from the ground.

ground resistance. The resistance of the groundportion of a circuit using the ground as anintegral part of the current path.

ground system. The portion of an antenna systemclosely associated with the ground, includingthe earth itself and any wires buried in it.

ground waves. Radio waves that travel alongthe surface of the earth inqfcad of ening upinto the sky, and that are affected by the pres-ence of the earth.

ground wire. A wire used to make connectionfrom electronic apparatus to a ground clampor other grounded object.

group velocity. The velocity of propagation of rfenergy when confined between reflecting me-diums, such as the walls of a waveguide, be-tween which it is bounced back and forth.The path travelled is consequently longer thanthe distance from the point of origin to thepoint of reception, so that the speed with whichthe signal is received is less than that of thewave components along the reflected path.

growler. An electromagnetic device used for lo-cating short-circuited coils in dynamo, gene -motor, or motor armatures.

guard band. A frequency band provided at eitherend of a channel to prevent interference be-tween adjacent channels.

guided wave. A wave whose propagation is con-centrated in certain directions.

gutta-percha. A natural vegetable gum resem-bling rubber, used principally as insulationfor wires and cables.

guy anchor. The buried weight or mass to whichthe lower end of a guy wire is attached.

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guy wire. A wire used to brace the mast or towerof a transmitting or receiving antenna system.

Hhairpin pickup coil. A hairpin -shaped, single -turn

coil used in vhf work to transfer energy froman rf generator, oscillator, amplifier, or trans-mitter to an antenna lead-in or to a succeedingstage.

hairpin tuning bar. A hairpin -shaped metal barinserted between the two halves of a doubletantenna and used to vary the over-all electri-cal length of the antenna.

halation. Spreading of light so as to produce aring of illumination surrounding the impactpoint of electrons on a fluorescent screen.

half -wave antenna. An antenna whose length isapproximately equal to one-half the wave-length to be transmitted or received.

half -wave line. A line electrically equivalent toa half wavelength at the operating frequency.

half -wave rectificatic.. Changing only one halfof each alternating current cycle into unidirec-tional current.

half -wave rectifier. A radio tube or other devicethat converts alternating current into pulsat-ing direct current by allowing current to passduring only one half of each alternating cur-rent cycle.

halo. See halation.ham. Slang term for an amateur radio operator.hard rubber. A brittle rubber compound used for

electrical insulation or as a dielectric.hard tube. A vacuum tube that has been evacu-

ated to a high degree.harmonic. An integral multiple of any frequency.

Thus, the second harmonic of a fundamentalfrequency would be equal to twice that funda-mental frequency.

harmonic analyzer. An instrument that measuresthe component pure sine waves of a complexwave.

harmonic antenna. An antenna whose length is anintegral multiple of the wavelength or the half -wavelength with which it is used.

harmonic attenuation. The elimination of a har-monic component by use of a pi network inwhich the shunt reactances are tuned to zerofor the frequency to be eliminated.

harmonic component. Any of the components(simple sinusoidal quantities) into which aperiodic quantity can be resolved.

harmonic content. The degree or numbers of har-monics in a fundamental complex frequencyoutput.

harmonic defector. A voltmeter circuit that meas-ures only a particular harmonic of a funda-mental frequency.

harmonic distortion. A distortion in which har-monics are added in the output signal thatwere not present in the input signal.

harmonic filter. An electronic circuit designed toattenuate harmonics in a particular piece ofelectronic equipment. See harmonic attenua-tion.

harmonic generator. A vacuum tube or other gen-erator used to produce a signal haying manystrong harmonies,

harmonic suppression. The prevention of the gen-eration of harmonics, or their attenuation aftergeneration.

harmonic wave analyzer. An instrument that pro-vides a means for determining the harmoniccontent of an af, rf, or ac output. A harmonicanalyzer.

Hartley oscillator. A vacuum tube oscillator eir-cuit using a tuned circuit that has a tapped,winding connected between the grid and theplate of the vacuum tube, with the tap going'to the cathode.

hash. Interference produced by man-made de-,vices, such as that produced by vibrators thathave excessive sparking at the contact points.

Hazeltine licensed. Radio apparatus that uses,Hazeltine patents under a licensing agreementwith the Hazeltine Corporation.

head. The cutting head in a recorder, a mechan-ism for cutting modulated grooves on a blank'disc. Also, a rectifier built in a probe, usedfor measuring rf voltages without upsettingthe circuit.

headphone. A small telephone receiver, usuallyheld against the ear by a clamp passing overthe head, used for private reception of radiqprograms or for reception of signals too weakto provide loudspeaker volume.

headphone adapter. A device that slips under thepower output tube, or is otherwise connectedto a radio receiver, to provide terminals towhich headphones can be connected.

headset. A pair of headphones attached to aheadband to hold the phones snugly againstthe ears.

heater. A filament used in vacuum tubes for thepurpose of supplying heat to an indirectlyheated cathode.

heater current. The current supplied to a vac-uum tube filament used only for heating pur-poses.

heater voltage. The voltage applied between theterminals of a vacuum tube filament used onlyfor heating purposes.

heat loss. Power dissipated as heat.heat waves. Infra -red radiation similar to radio

waves, but of higher frequency.Heaviside layer. A layer of ionized gas which

exists in the region between 50 and 400 milesabove the surface of the earth, and which re-flects radio waves back to earth under certainconditions. Also called the Kennelly -Heavisidelayer.

height control. The control in a television re-ceiver that adjusts the picture size in a verti-cal direction. Also called the vertical size con-trol.

Heising modulation. A modulation system in whichthe plates of both the rf oscillator and themodulator tube are fed through a single com-mon choke having high impedance at bothaudio and radio frequencies. This choke pre-vents any change in the total plate currentdrawn by the two tubes together. Therefore,the of plate current variation in the modula-tor tube produces a similar but opposite ofvariation in the plate current of the rf os-cillator tube. Also called constant -currentmodulation.

helical. Having the shape of a helix or coil.Spiral.

helix. A coil wound in spiral form. The shape ofa machine screw thread.

38

henry (h). The unit of inductance. A device hasan inductance of 1 henry when an electromo-tive force of 1 volt is induced in it by a cur-rent changing at the rate of 1 ampere persecond.

heptode. A vacuum tube having seven electrodes.

hermetically sealed. Sealed so as to be air -tight.

Hertz antenna. An antenna that is electrically in-dependent of the ground.

heterodyne. Pertaining to the production of sumand difference frequencies and their associatedharmonics by combining two frequencies.

heterodyne frequency. A frequency, produced bycombining two other frequencies, which is theirnumerical sum or difference. A beat frequency.

heterodyne frequency meter. See heterodynewavemeter.

heterodyne harmonic analyzer. A circuit in whicha complex input voltage is examined by beat-ing it with a variable frequency oscillator sig-nal, and filtering the resultant beats to sepa-rate the harmonics.

heterodyne interference. Interference between twostations transmitting on nearly the same fre-quencies so their waves produce a beat notethat causes an audible tone in receivers.

heterodyne reception. A process of changing thecarrier frequency of an incoming signal bycombining it with a locally generated signal.Usually called superheterodyne reception.

heterodyne wavemeter. A wavemeter used to de-termine the frequency of a signal by hetero-dyning the known frequency of its internaloscillator with the received rf frequency, andtuning the internal oscillator to produce azero beat. Also called heterodyne frequencymeter.

heterodyne whistle. A steady squeal heard in areceiver due to a beat formed by heterodyneinterference between stations having nearlyequal carrier frequencies.

hexode. A vacuum tube having six electrodes.high -angle radiation. Radiation from a transmit -

Ling antenna in a vertical or nearly verticaldirection.

high definition. The television or facsimile equiva-lent of audio high fidelity, in which the repro-duced image contains as nearly as possible allpicture elements, accurately reproduced, witheach detail clearly visible.

high fidelity. The ability of an audio component,amplifier, or system to reproduce with a mini-mum of distortion the full audio range of fre-quencies.

high-fidelity receiver. A receiver capable of re-producing audio frequencies in a range from50 to about 8000 cycles or wider without seri-ous distortion, so that the reproduced programcannot be distinguished from the originalstudio program.

high -frequency resistance. The total effective re-sistance of a circuit to high -frequency cur-rents, including eddy current, hysteresis, di-electric, corona, and ohmic losses.

high -frequency trimmer. In a superheterodyne re-ceiver, the trimmer condenser that controlsthe calibration of a tuning circuit at the high -frequency end of a tuning range.

high-level detector. See power detector.high-level modulation. Modulation at a point in a

transmitter where the power level is approxi-

mately the same as at the output of the trans-mitter.

highlight. Pictorially, a point of great illumina-tion or the brightest parts of a reproducedimage.

high -mu tube. A tube having a high amplificationfactor.

high-pass filter. A filter network designed to passall frequencies above a cut-off frequency valuewhile attenuating or rejecting lower frequen-cies.

high Q. High ratio of reactance to ac resistancefor any resonant circuit or coil.

high -resistance voltmeter. A voltmeter having avery high resistance, so that little current isdrawn by the meter from the circuit in whicha measurement is made.

high-tension. A term applied to circuits handlingthousands of volts.

high -vacuum tube. A vacuum tube that has beenevacuated so thoroughly that gaseous ioniza-tion cannot occur during normal operation.

high -voltage power supply. Equipment designedto provide high voltage, as for acceleration ofthe beam in iconoscopes or Kinescopes.

hill -and -dale recording. See vertical recording.hissing. A noise encountered in sensitive radio

receivers due to feedback or to circuit and tubeshot effects.

H network. A network composed of five im-pedance or resistance sections, connected toresemble the letter "H."

hold controls. In a television receiver, the twomanually adjusted controls that adjust thenatural oscillating frequencies of the oscilla-tors used in the horizontal and vertical sweepcircuits. Also called speed or framing controls.

homing. An aviation direction finding system inwhich a non -directional signal is radiated bya transmitter at an airport or carrier, and afixed directional antenna is used on the air-plane so that maximum signal is received onlywhen the plane is headed toward the trans-mitter.

honeycomb coil. A coil wound in a criss-cross orbasket -weave manner to reduce distributed ca-pacity. Also called lattice -wound coil.

hookup. A diagram giving circuit connections fora receiver, amplifier, or transmitter.

hookup wire. Tinned and insulated soft drawncopper wire used in wiring radios. TV sets,switchboards, etc.

hop. An excursion of a radio wave from theearth to the ionosphere and back to earth, intraveling from one point to another. Also, aslang term for sensitivity.

horizon. In radio -wave propagation over theearth, the line that bounds that part of theearth's surface reached by the direct wave. Ona spherical surface, the horizon is a circle.

horizontal. Level. From side to side.horizontal afc. An automatic frequency control

circuit used to lock the horizontal sweep of aTV receiver to the average of the sync pulses.

horizontal amplitude control. See width control.horizontal blanking. The application of cut-off biai

to a cathode ray tube during the horizontalretrace.

horizontal blanking pulse. The pulse that cuts off39

the electron beam while it is returning to theleft side of the screen of a cathode ray tube.

horizontal centering control. A control providedin a television receiver or cathode ray oscillo-scope to shift the position of the entire imagefrom side to side. Also called horizontal posi-tioning control.

horizontal deflecting electrode. One of the cath-ode ray tube electrodes to which voltage is ap-plied to move the electron beam from side toside.

horizontal drive control. The control on an elec-tromagnetically deflected television receiverthat adjusts the grid input on the horizontaloutput tube, thus affecting both the width andthe linearity of the horizontal sweep. Alsocalled horizontal peaking control.

horizontal flyback. In a television system, theright -to -left return motion of the electron beamfrom the end of one line to the beginning ofthe next.

horizontal frequency. In television, the number oftimes per second the spot sweeps across thescreen in the horizontal direction. The hori-zontal repetition rate.

horizontal hold control. The control that adjuststhe frequency of the horizontal sweep oscilla-tor in a television receiver so that it can belocked in with the sync pulses. Also called thehorizontal speed or framing control.

horizontal linearity control. In television, a con-trol provided to adjust the uniformity of thedistribution of picture elements in a hori-zontal direction.

horizontally polarized wave. An electromagneticwave in which the electric field is parallel tothe surface of the earth.

horizontal peaking control. horizontal drivecontrol.horizontal positioning control. See horizontal cen-

tering control.horizontal repetition rate. See horizontal fre-

quency.

horizontal resolution. The definition or clarity ofa television image in a horizontal line.

horizontal retrace. See horizontal flyback.horizontal scanning frequency. See horizontal fre-

quency.

horizontal size control. See width control.horizontal speed control. See horizontal hold con-

trol.

horizontal sweep. In television, the circuit thatproduces the horizontal scanning voltage.

horizontal synchronization. Making the horizontalscanning at the receiver occur at the samerelative time as the horizontal scanning at thecamera.

horizontal synchronizing pulse. The pulse sent atthe end of each line for controlling the hori-zontal sweep rate. The line synchronizingpulse.

horn. A tapering tube used in some loudspeakersin place of a baffle. The smaller end of thehorn is the throat, the larger the mouth.

horn radiator. A tapered metal box used as aguide for radiated waves.

horsepower. A unit of power, the rate of doingwork. One horsepower is mechanically equiva-lent to 33.000 foot-pounds per minute or 550foot-pounds per second, and is electricallyequivalent to 746 watts.

horseshoe magnet. A magnetized steel bar bentinto the shape of a horseshoe.

hot. Connected, alive, energized, not grounded.Heated.

hot -cathode tube. A vacuum or gaseous tube inwhich the cathode is heated to provide elec-tron emission.

hot-wire ammeter. An ammeter that depends forits action on the expansion of a fine wire underthe influence of the heat produced in it by thepassage of the current to be measured.

howl. An undesirable audio -frequency oscillationoccurring in a radio or amplifier system, dueto either electrical or acoustic feedback.

H pad. An attenuation network having its ele-ments arranged like -the letter H, with a con-stant input and output impedance.

H plane. The plane of an antenna in which themagnetic field lies, perpendicular to the Eplane.

hum. A low audio frequency, having the samefrequency as that of the power supply or aharmonic thereof, introduced into the signalpaths by induction, leakage, or insufficient fil-tering, and heard in the background of a re-ceived radio program, or appearing across atelevision image in the form of one or twohorizontal bars.

hum -bucking coil. An extra coil placed on the cen-ter pole of an electrodynamic loudspeaker andwired in series with the voice coil so that humcurrents induced in both coils by the field coilwill cancel.

hum modulation. Hum audible only when a sta-tion is tuned in, originating in an rf stage.

hunting. Speed variation or oscillation about theaveragea motor.

hydrometer. A device used to measure the spe-cific gravity of a liquid.

hygroscopic. Readily absorbing and retainingmoisture.

Hypes horn. A loudspeaker horn having a modi-fied exponential rate of growth.

hypotenuse. The side of a right triangle oppositethe right angle.

hysteresis. The tendency of a ferromagnetic ma-terial to retain magnetism or to oppose achange in magnetism, resulting in a loss ofenergy.

hysteresis loop. A graph showing the relation be-tween magnetizing force and flux density overa complete cycle of magnetization and de-magnetization.

hysteresis loss. Energy loss in a magnetic sub-stance exposed to a constantly changing mag-netic field due to internal friction, appearing asheat.

iconoscope. A cathode-ray pickup tube used inelectronic television cameras. It converts eachpicture element of the scene into a correspond-ing electrical signal. Scanning of the image isaccomplished by making an electron beamsweep back and forth across the mosaic manytimes per second.

identification of friend or foe (IFF). A system ofchallenge and response by radar, involvingtransmission of coded signals.

40

Idler pulley. A pulley used to maintain tensionon or to change the direction of motion of abelt or cord. Its shaft does not rotate anyother part.

ignition interference. Interference produced bysparks or other ignition discharges, or equip-ment in which there are loose contacts or con-nections.

ignitor. An electrode made of highly resistivematerial, partly immersed in the mercury -pool cathode of an ignitron tube and used toactivate the ignitron by starting the ionizationprocess.

ignitron. A half -wave mercury-vapor tube usedas a high -power rectifier.

Illumination. The amount of light flux falling ona surface, usually measured in foot candles.

illuminosity meter. A device for measuring lightflux or amount of illumination, generally usinga photoelectric cell to convert light energyinto an electric current that can be measured.

Image. A reproduction of a person, object, orscene, such as that produced by a televisionreceiver.

image antenna. An imaginary antenna consideredthe source of reflected waves.

image dissector. A television pickup tube thatconverts the optical image to an equivalentelectron image and then scans this electronimage by allowing a small portion of it at atime to pass into an ,electron multiplier tube.

image distortion. Faulty transmission or repro-duction of the scene scanned by a televisioncamera.

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image frequency. A frequency on the opposite sideof the oscillator frequency from that of thedesired frequency, and differing from the os-cillator frequency by the i-f value. For exam-ple, in a superheterodyne receiver in whichthe oscillator operates above the incoming sig-nal frequency, the image frequency is equal tothe sum of the oscillator frequency and thei-f value, and the image frequency is above thedesired signal frequency by twice the i-f value.

image interference. Interference in which twostations are heard at the same time, one beingthe desired station. and the other being anundesired station at the image frequency.

image -interference ratio. A superheterodyne re-ceiver rating indicating how effectively the rftuned circuits ahead of the first detector canreject signals at the image frequency whentuned to a desired frequency.

Image Orthicon

image orthicon. A television camera tube in whicha low -velocity electron beam is used to pickup the image signal; then an electron multi-plier in the tube is used to ampuly it.

image ratio. The ratio of the strength of a sig-nal to its image, used to indicate selectivity ofa receiver.

image reconstructor. The picture tube or otherdevice used in a television receiver to convertthe received picture signals into an image ofthe scene originally televised.

imaginary number. The square root of a nega-tive number. In formulas the letter j indicatesthe square root of minus one.

impact excitation. The starting of damped oscil-lations in a circuit by a sudden pulse. Shockexcitation.

impedance. The total opposition a part or circuitoffers to the flow of alternating current at aparticular frequency. A combination of re-sistance and reactance measured in ohms.

impedance bridge. A device to measure the com-bined resistance and reactance of a part.

impedance coil. See choke coil. An inductor.

impedance coupling. Coupling between stages bya circuit resembling resistance coupling, withone or both resistors replaced by choke coils.

impedance match. A condition in which the im-pedance of a component or circuit is equal tothe impedance of the source to which it is con-nected.

impedance -matching transformer. A transformerused to provide an impedance match betweentwo or more circuits.

implode. To burst inward, as does a televisionpicture tube when cracked. The high vacuumcauses the external pressure to be so greatthat the glass fragments are forced inward ata high velocity.

impregnate. To treat a component so as to makeit moisture resistant by filling the excess spacein its container with a material such as waxor pitch. Also applied to the coating of a partwith a similar material.

impulse. See pulse.impulse noise. Random, sharp bursts of noise.inactive lines. The television image lines not

visible on the picture tube screen, those ofthe 525 image lines that are blanked out be-tween fields.

incident light. Light falling on a surface.incident wave. A wave striking an object.inclination. The angle a line or surface makes

with another line or surface.increment. A change in the value of a variable.incremental permeability. The permeability effec-

tive in a core when an ac fluctuation in cur-rent is superimposed on a dc current.

index. The small number in the angle of a radi-cal sign, indicating the particular root to be

41

extracted. Examples: In the index is 4;In .04, the index is 3.

Index of refraction. A number indicating howmuch a ray of light will be bent out of itsnormal path when passing from one materialinto another. It is equal to the speed of lightin one material divided by the speed of light inthe other material.

indicator. An instrument used to detect the pres-ence of an electrical quantity without neces-sarily measuring it.

Indirectly heated cathode. In a vacuum tube, acathode heated by a separate filament.indirect scanning. A method of scanning in which

a beam of light is moved across a scene or pic-ture, and the light reflected from the illumi-nated scene is picked up by a photocell orgroup of photocells.

Indirect view. A television receiver in which theimage is optically projected from the cathoderay tube to a larger viewing screen.

indirect wave. Sky wave.indoor .antenna. A receiving antenna system lo-

cated entirely inside a building.induced charge. An electrostatic charge produced

on an object by an electric field in the vicin-ity.

induced current. A current due to an inducedvoltage.

induced voltage. A voltage produced in a circuitby changes in the number of magnetic linesof force linking or cutting through the con-ductors of the circuit.

inductance (L). The property of a circuit or coilthat causes an electromotive force (voltage) tobe set up because of a change in current in thecircuit or coil, or that determines how muchelectromotive force will be induced in one oftwo neighboring coils or circuits by a changein the other. Inductance is effective only whena varying or alternating current exists, andhas no effect on direct current. The basic unitof inductance is the henry. A circuit has aninductance of 1 henry when a change of cur-rent of 1 ampere per second induces an electro-motive force of 1 volt.

inductance bridge. A form of Wheatstone bridgecircuit used to determine inductance values.

inductance -tube modulation. Frequency modula-tion by means of an oscillator control tubethat acts as a variable inductance in parallelwith the tank circuit of an rf oscillator, caus-ing the oscillator frequency to vary in pro-portion to the of voltage applied to the grid ofthe oscillator control tube.

Induction. A coupling produced by magnetic linesof force whereby the variable flow of currentthrough one coil produces a voltage in a near-by coil even though there is no electrical con-nection between the coils. Also, the productionof a charge or of magnetism by the presenceof an electric or a magnetic field.

induction coil. A device with some form of inter-rupter for changing direct current into high -voltage alternating current.

induction compass. A compass whose indicationsdepend on a coil revolving in the magnetic fieldof the earth. An earth inductor compass.

induction field. The portion of the electromag-netic field produced by a transmitting antennathat acts as if it were permanently associatedwith the antenna. The radiation field, on theother hand, breaks away from the antenna toform radio waves.

induction heating. An industrial or laboratoryprocess in which rf power is coupled by highlyefficient coils into a load for melting, weldingor brazing, or heating.

induction motor. An electric motor operated onthe principle that a pivoted closed loop of wirewill rotate essentially in step with a rotatingmagnetic field.

inductive coupling. A form of coupling in whichenergy is transferred from a coil in one cir-cuit to a coil in another circuit by induction.

inductive feedback. Feedback of energy from theplate circuit to the grid circuit of a tube byinductive coupling.

Inductive reactance. Reactance due to the induct-ance of a coil or other part in an alternatingcurrent circuit. Inductive reactance is meas-ured in ohms, and is equal to the inductancein henrys multiplied by the frequency in cycles.times the number 6.28.

inductor. Inductance. Coil.inert gas. One of a group of gases including

helium, neon, argon, krypton, and xenon, thatwill not combine with another element.

inertia. The property of matter that tends toprevent motion, or resists a change of motion.

infinite. Without limit.

Infinite -impedance detector. See C bias detector.infinite line. An imaginary transmission line that

has all the characteristics of an ordinary line.but is infinitely long.

infinity. A number greater than any definite num-ber.

infra -black region. See blacker -than -black region.

infra -red rays. Rays of longer wavelength thanvisible light rays, lying Just beyond the redend of the spectrum. Heat rays.

infrasonic. Having a frequency below the audiblerange.

injection grid. A grid element placed in a vacuumtube in such a way that it has reasonable con-trol over the electron stream without causinginteraction between itself and the control grid.

ink -vapor recording. The type of electromechani-cal facsimile recording in which vaporized inkparticles are directly deposited upon the recordsheet.

in phase. Having the same frequency and pass-ing through maximum values at the same in-stant of time, exactly in step.

input. The current, voltage, or power fed into acircuit or device. Also, the terminals to whichthe incoming signal is applied.

input admittance. The reciprocal of the imped-ance between the grid and the cathode of atube, determined by the internal tube capaci-ties and the coupling effects of the grid -to -plate capacity.

input capacity. The sum of all the direct inputcapacities between the grid and all other elec-trodes of a vacuum tube, plus the grid -platecapacity as increased by the Miller effect.

input gap. Gap in which the initial velocity mod-ulation of the electron stream is produced in aklystron. The buncher gap.

input impedance. The ratio of the ac voltage ap-plied to the input terminals of a circuit ordevice to the alternating current thereby pro-duced.

42

input transformer. A transformer used to deliverenergy to the input of a device or amplifier.

insertion loss. The ratio (expressed in decibels)of the power delivered before, to the powerdelivered after, the insertion of an apparatusin a transmission system.

instantaneous power output. The rate at whichenergy is delivered to a load at a particularinstant..

instantaneous recording. A recording that can beplayed without further processing.

instantaneous value. The value of an alternatingcurrent, voltage, or power at any one point inits cycle.

instrument landing system (ILS). A radio systeinfor guiding an airplane into a landing by in-strument indications when visibility is limited.

instrument multiplier. A highly accurate series re-sistor used to extend the voltage range of ameter.

instrument shunt. A highly accurate low -value re-sistor connected in parallel with a meter toextend its current range.

insulated carbon resistor. A carbon resistor en-cased in a molded ceramic, fiber, or plastichousing.

insulating tape. Tape impregnated with insulat-ing material, usually adhesive and used tocover joints in insulated wire or cables. Alsorubber tape.

insulation. Any material that has a sufficientlyhigh electrical resistance to separate one elec-trical circuit, part, or wire from others. Cot-ton. silk, baked enamel, mica, porcelain. rub-ber, and Bakelite are a few of the common in-sulating materials used in radio.

insulation resistance. The electrical resistance be-tween two conductors separated by an insu-lating material.

insulator. An object that offers a great deal ofopposition to the movements of electrons, usedfor supporting or separating conductors.

Integer. Any whole number, without fractionsor decimals.

integral sign. The sign I, used in higher mathe-matics to indicate that the operation of in-tegration (finding the sum of small elements ordifferentials) is to be performed.

integrating circuit. A low-pass filter circuit, onein which the output is the sum of the inputpulses when these pulses occur at a rate fasterthan the discharge time of the circuit.

intelligence signal. The electrical signal that cor-responds to the information or intelligence be-ing handled, such as sound waves, televisionscenes, or code; also known as the low -fre-quency signal.

intensifier ring. A third anode in a cathode raytube, consisting of a coating on the inside ofthe glass envelope. The application of a highpositive potential to the intensifier ring in-creases the velocity of the electron stream, con-sequently increasing the intensity of the light.

intensity. Strength or value.

Intensity modulation. The process of applying avoltage to the grid or cathode of a cathode raytube to vary the intensity of the spot as itsweeps across the screen. Brilliance modula-tion, or Z-axis modulation.

intensify of illumination. The brightness of anilluminated surface. Intensity of illuminationis normally indicated in foot-candles and is in-

versely proportional to the square of the dis-tance from the source.

interaction gap. In a klystron, the space betweenthe buncher grids or between the catcher grids,in which the electron stream interacts with anrf field.

intercarrier-noise suppression. *A means for sup-pressing the noise otherwise heard in a high -gain receiver when it is tuned between sta-tion carriers. The audio input of the receiveris blocked automatically when no signals existat the second detector.

latercarrier sound system.. A method of utilizingthe 4.5 -me beat between video and sound car-riers as an i-f frequency for the sound signalof the television receiver. Also called inter -modulation sound system.

Intercom. See intercommunication system.intercommunication system. An amplifier system

that provides two-way communication betweentwo or more points in a building.

interelectrode capacity. The direct capacity thatexists between two electrodes in a vacuumtube.

interference. Noises or undesired programs thataffect the reception of a desired program.

interference eliminator. Any device designed forthe purpose of removing or reducing inter-ference.

interference filter. A device used on a source ofinterference or on a receiver to attenuate oreliminate noise.

interference guard bands. Bands of frequenciesin which no signals are transmitted, existingon either side of a channel, providing separa-tion between signals of stations having adja-cent frequency assignments to prevent adja-cent -channel interference.

interference pattern. Any interfering pattern seenon a television screen, caused by hum, noise,etc.

interlaced scanning. In television, a system inwhich every other line of the image is scannedduring one downward sweep of the scanningbeam, and the remaining lines are scannedduring the next downward sweep of the scan-ning beam.

interlock. A system that makes it impossible toopen or close certain switches or relays untilcertain actions have taken place. For example,interlocking relays and switches may make itimpossible to apply plate voltage to mercuryvapor rectifier tubes until their filaments havereached operating temperature. Also, similarswitches used on doors of transmitters or ontelevision sets to automatically break the highvoltage supply circuits when doors are openedor shields removed, to protect the operatoror serviceman.

intermediate frequency ti -H. The frequency pro-duced by the heterodyne process, equal to thedifference between the frequency of the localoscillator and the incoming signal.

intermediate -frequency amplifier. The section of asuperheterodyne receiver designed to amplifysignals with high efficiency at a predeterminedfrequency called the intermediate frequency ofthe receiver.

intermediate -frequency harmonic interference. Akind of interference resulting when harmonicsof the i-f signal get back into the rf inputstages of a superheterodyne and come throughthese stages along with the desired signal.

intermediate -frequency transformer. A trans-former used at the input or output of an 1-f

43

amplifier stage in a superheterodyne receiverfor coupling purposes and for providing selec-tivity.

intermittent duty. Non -continuous operation.

intermittent -duty rating. The rating of a devicewhen operated or specified intervals of timeother than continuous duty.

intermittent reception. A type of faulty receptionin which a receiver performs normally for atime, then becomes dead or otherwise defec-tive, with the process repeating itself at regu-lar or irregular intervals.

intermodulation. A process wherein two or moredifferent signal frequencies combine in a non-linear circuit to produce new frequencies cor-responding to sums and differences of thefundamental frequencies and their harmonics.

intermodulation distortion. Signal components inthe output not present in the input that havefrequencies equal to the sums and differencesof integral multiples of component frequenciespresent in the input signal.

intermodulation interference. Station interferencethat occurs when two undesired signals whosefrequencies differ by exactly the i-f value of asuperheterodyne receiver reach the first detec-tor, and there produce an 1-f beat signal with-out the aid of the local oscillator.

intermodulation sound system. See intercarriersound system.

internal resistance. The resistance inside a bat-tery, generator, or circuit component.

International Morse Code. The dot and dash codeused universally for radiotelegraphy, and forwire telegraphy in some European countries.The Continental Code.

interpolation. The process of estimating the valueof a quantity between two known values.

interrupted continuous wave (icw). A continuouswave modulated by an audio -frequency tone,then code keyed.

interrupter. Apparatus for breaking up a con-tinuous current into successive pulses.

interstage. Between stages.

interstage transformer. A transformer used toprovide coupling between two vacuum -tubestages.

interval timer. An electronic tube device used tomeasure time intervals.

intrinsic impedance. The impedance to an electro-magnetic field, expressed as a ratio of thestrengths of the electric and the magneticfields. In a loss -free material or free space, it Isdetermined by the ratio of the permeabilityand the dielectric constant.

inverse feedback. Negative feedback, also calleddegeneration or stabilized feedback. A fractionof the output signal of an amplifier stage isintentionally fed back to the input so it is outof phase, thereby reducing distortion andnoise, permitting greater undistorted poweroutput. It also reduces amplification.

inverse feedback filter. A resonance bridge cir-cuit used at the output of a high -selectivityamplifier. in which the impedance is adjustedso that the feedback output is zero for theresonant frequency but increases rapidly asfrequency departs from this value.

inversely proportional. Related in such a way thatwhen one value increases, the other decreasesa proportionate amount, and vice versa.

inverse peak voltage. The maximum ac voltage

that can be applied to a rectifier tube with-out arcing or flashover when the filament ispositive and the plate negative.

inverted amplifier. See grounded -grid amplifier.inverted L antenna. The conventional antenna

used for broadcast reception, having a longhorizontal portion suspended between insu-lators, with the single -wire vertical lead-inconnected to one end of the horizontal portion.

inverter. Any device used to change de to ac.

ion. An electrified particle, such as an atom ormolecule, having either fewer or more elec-trons than normal. A positive ion is a par-ticle that has lost electrons, and a negativeion is one that has acquired more electronsthan normal.

ionization. An action whereby atoms or mole-cules of gas in an electronic tube are con-verted into electrically charged ions, whichare attracted by charged electrodes. Ionizationmakes a gaseous tube more conductive thanan equivalent vacuum tube.

ionization current. Current flow between two op-positely charged electrodes in an ionized gas.

ionization potential. The voltage at which suffi-cient current will flow to ionize the gas in atube.

ionization pressure. An increase in the pressurewithin a gaseous tube due to ionization of thegas.

ionization time. The time between the momentof application of voltage and the ionization ofthe gas.

ionized layer. See Kennelly -Heaviside layer.ionosphere. The part of the earth's outer atmos-

phere where ions and electrons are present inquantities sufficient to affect the propagationof radio waves.

ionospheric storm. A period of disturbance in theionosphere, during which radio waves are re -fleeted in abnormal ways.

ionospheric wave. A radio wave that is reflectedfrom the ionosphere. A sky wave.

ion spot. An insensitive dark spot on the screenof a cathode ray tube resulting from ionicbombardment of that spot.

ion trap. A coil or permanent magnet placed onthe neck of the cathode ray tube to straightenthe electron stream so that it can proceed tothe screen, after this stream has been deflectedin the process of bending aside the ion stream.A beam bender.

IR drop. Voltage drop produced across a resistor(R) by the flow of current (I) through it.

1212 loss. Power loss due to current flow throughresistance.

iron -core coil. A coil wound on a form inside ofwhich iron laminations are inserted.

iron -core transformer. A transformer in whichiron makes up part or all of the path for mag-netic lines of force traveling through the trans-former windings.

iron loss. Power loss occurring in iron cores ofelectric machines, coils, transformers, etc., dueto hysteresis and eddy currents.

iron -vane instrument. A meter in which the mov-able element is an iron vane, which is drawninto the magnetic field produced by the flowof the current being measured.

Isolantite. A high -quality insulating material44

used in the construction and mounting of radioparts, particularly those used in ultra -high -frequency circuits.

isolation network. A network inserted in a circuitor transmission line to prevent interaction be-tween circuits on each side of the insertionpoint.

iterative impedance. The characteristic or surgeimpedance of a transmission line or filter sec-tion.

Jjack. A plug-in spring terminal widely used in

radio apparatus for temporary connections.J antenna. A half -wave antenna, fed at the end

by a quarter -wave line section so the two re-semble the letter J.

JAN specification. Joint Army Navy specification.

jewel bearing. A small piece of natural or syn-thetic jewel, usually sapphire, carefully groundto form a bearing for the pivot of a metermovement.

jitters. Distortion in a received television orfacsimile picture caused by momentary errorsin synchronization between scanner and re-corder.

joule. The unit of electrical work or energy. Onejoule equals one watt -second.

Joule's law of heating. The heat produced in aconductor is proportional to the resistance ofthe conductor, the square of the current, andthe time.

jumper. Any conductor used to connect twopoints together or short out a part temporarily.

junction. A joint or connection. Also, a point ofcontact between two dissimilar metals or ma-terials.

junction box. A box into which wires or cables areled and connected.

Kkeep -alive anode. An auxiliary electrode in a mer-

cury pool tube that keeps the mercury heatedand thus ionized.

keeper. A piece of iron used to close the mag-netic circuit of a permanent magnet to preventloss in magnetic strength.

Kelvin scale. The absolute temperature scale; theequivalent Centigrade value, plus 273.1.

Kennelly -Heaviside layer. A layer of ionized gassupposed to exist in the region between 50 and400 miles above the surface of the earth. Itreflects radio waves to earth under certain con-ditions, making possible long-distance radioreception.

Kenotron. A high -vacuum rectifier tube.Kerr cell. A device used in some mechanical tele-

vision systems to modulate a light beam withtelevision signals. The cell rotates a beam ofplane -polarized light in proportion to the volt-age applied between the two plates of the cell.

key. A lever switch designed for rapid openingand closing of a circuit during transmission ofcode signals. Also, a lever switch used on tele-phone switchboards to control speech circuits.

key -click filter. A filter that attenuates the surgeproduced when the keying circuit of a trans-mitter is opened or closed.

key clicks. The noise caused by the sharp cur-rent change when a sending key is opened orclosed.

keyer. A device that changes the amplitude orfrequency of the output of a transmitter inaccordance with the intelligence to be trans-mitted.

keying chirps. Peculiar sounds accompanyingcode signals When the transmitter is unstableand shifts in frequency each time the sendingkey is closed.

keystone correction. To cause the horizontal sweepwidth in an iconoscope to increase when ver-tical scanning deflects the beam to the part ofthe mosaic nearest the electron gun, resultingin a rectangular rather than a keystone -shapedelectron image.

keystone distortion. A form of distortion in whichthe television image takes the shape of a trape-zoid, because the electron gun is not at rightangles to the mosaic. This makes the electronpath to the top of the picture longer than thatto the bottom, and consequently the sweep iswider at the top than at the bottom.

keystone -shaped image. A reproduced image widerat the top than at the bottom (or vice versa).

keystoning. The effect produced when the elec-tron gun of a cathode ray television cameratube is placed at an angle with the principalaxis of the tube, resulting in a keystone -shapedscanning pattern.

kickback. The counter -electromotive force pro-duced in a coil when the current through it isstopped and the magnetic field collapses.

kickback power supply. See flyback supply.kilo. Metric prefix meaning 1000.

kilocycle. One thousand cycles.

kilogauss. A unit of flux density equal to 1000gausses or 1000 lines of flux per square centi-meter.

kilovolt. One thousand volts.kilovolt -amperes. A unit of apparent power, equal

to 1000 volt-amperes.

kilovoitmeter. A voltmeter scaled in thousands ofvolts.

kilowatt. A unit of electrical power equal to 1000watts.

kilowatt-hour. A unit of electrical energy, equalto 1000 watt-hours. (Watts X hours ±. 1000.)

kinescope. A cathode ray tube used in televisionreceivers for reproducing the scene being tele-vised. A picture tube.

kinetic energy. The energy (ability to work) amoving object possesses by virtue of its mo-tion.

Kirchhoff's Current Law. A fundamental electricallaw which states that the sum of all the cur-rents flowing to a point in a circuit is equalto the sum of all the currents flowing awayfrom that point.

Kirchhoff's Voltage Law. A fundamental electricallaw which states that the sum of all the volt-age sources acting in a complete circuit isequal to the sum of all the voltage drops inthat same circuit.

klystron. A tube in which the speed rather thanthe number of electrons is controlled by the in-put signal. Elements called the buncher gridsvelocity modulate the electron stream so theelectrons collect in bunches in the drift space.

45

The catcher grids then extract energy fromthe electron bunches.

klystron oscillator. A microwave oscillator thatuses a klystron to get considerable rf powerat frequencies above 300 megacycles.

knee. An abrupt change in direction betweentwo fairly straight segments of a curve.

knife switch. A switch in which one or more fiatmetal blades, each pivoted at one end, makecontact with gripping spring clips to completethe circuit.

knob. A radio part, usually round but sometimeshaving a pointer or other position -indicatingmeans, attached to the end of a control shaftor lever for ease or safety of operation.

Llaboratory. A place where scientific experiments

and investigations are carried out, or whereequipment is developed.

labyrinth. See acoustic labyrinth.lacquer discs. Phonograph records usually of

metal, glass, or paper, coated with a lacquercompound and used either for instantaneousrecordings or lacquer masters.

ladder network. An adjustable attenuator net-work of the step type in which the steps areof known attenuation, and the network pre-sents a known and constant load to the signalsource. Also, a sequence of L, T. H, or pinetworks.

lag. The difference between the time that twoalternating quantities having the same fre-quency pass through values; theone that reaches a particular point in a cyclelast is said to lag behind the other.

lagging current. An alternating current that isretarded by the inductance of the circuit, sothat its changes occur after the voltage,changes have occurred. When there is onlyinductance in the circuit, the current lags 90degrees behind the voltage.

lag screw. A screw used for fastening objects tobrick or masonry.

lambert. The unit of brightness, equal to onelumen per square centimeter.

laminated. Made of thin layers, strips, or plates.lamination. A thin layer, strip or sheet. Specifical-

ly, one of iron or steel, used to build the coreof a transformer or other device designed tooperate at audio or power frequencies. Also,a thin layer of plastic -impregnated cloth, usedin making insulating sheets or tubes.

lamp. An artificial source of light, infra -red, orultra -violet radiation.

land. The surface between two grooves on aphonograph record.

land line. A telegraph or telephone line.L antenna. An antenna consisting of one or more

horizontal wires with a vertical lead-in con-nected at one. end. An inverted L antenna.

lap dissolve. The effect of reducing the contrastand brightness of one picture to zero whilesimultaneously increasing, the contrast andbrightness of a second picture from zero tomaximum so that one fades in as the otherfades out on a television screen.

lapel microphone. A small microphone that canbe attached to a lapel or pocket by means ofa clip.

lapping. Finishing quartz crystal blanks by pre-cision grinding.

lap winding. A type of winding of an armature inwhich each coil terminates at the next adjacentcommutator segment.

laryngaphone. A throat microphone.latent image. Stored picture information, such as

that contained in the charged globule -capaci-tances of the iconoscope.

lateral force. Force exerted from the side.lateral recording. A recording in which the groove

modulation is cut so that the phonographneedle moves from side to side during play-back.

latitude. Distance north or south of the geo-graphical equator, measured in degrees, min-utes, and seconds, ranging from 0° at theequator to 90° at either pole.

lattice network. A network of four branches, twoin series between input and output, one oneach side of the line, and the remaining twocross -connected from input to output so thatone goes from an input to the diagonally op-posite output terminal and the other one goesbetween the remaining pair of terminals.

lattice -wound - coils. Coils in which the windingsare criss-crossed.

launching. Transferring energy from a coaxialcable or shielded paired cable into a waveguide.

law of electric charges. Like charges repel eachother; unlike charges attract each other.

law of magnetism. Like poles repel; unlike polesattract.

law of position. The relationship that exists be-tween the focal length and the distances of

1object and image from an optical lens: -1 1

-= -, where P = distance from lens to ob-ject, Qf = distance from lens to image, andf = focal length of lens.

layer -built battery. A battery in which fiat, wafer-like cells are laid one on top of the other,eliminating waste space.

layer windings. A coil -winding method in whichadjacent turns are laid side by side along thelength of the coil form, then succeeding turnsare placed over the first layer in the sameside -by -side manner.

layout. A diagram indicating the placement ofparts on a panel or chassis.

LC product. Inductance multiplied by capaci-tance.

LC ratio. Inductance divided by capacitance.

lead (pronounced feed). Any connecting wire, suchas a battery lead, a test lead, etc. Also, theopposite of lag. When two alternating quan-tities have the same frequency but do not passthrough corresponding values at the same in-stant, the one which reaches a particular pointin a cycle first is said to lead the other.

lead (pronounced led). A soft gray metal used instorage batteries, solder, and for shieldingcables.

lead cell. The common storage battery cell thatuses plates of lead compounds for the positiveand negative electrodes.

lead-in. The portion of an antenna system thatconnects the main part of an antenna to the

46

input of a receiver or to the disconnectingswitches or instruments of a transmitter or itstuning house.

lead-in insulator. A porcelain tube inserted in ahole drilled through an outer wall or windowframe of a house through which the lead-inwire of the antenna is run.

lead-in spiral. A blank spiral groove at the be-ginning of a record, used to guide the phono-graph needle into the recorded grooves.

lead screw (pronounced teed screw). In recording,the threaded rod that leads the cutter or re-producer across the surface of the disc.

leakage. Undesirable flow of current through orover the surface of an insulating material.Also, magnetic flux that takes a short-cut pathso that it does no useful work. Also, the es-cape of a portion of an electromagnetic fieldalong an undesired path.

leakage current. A current flowing between twoor more electrodes of a tube by any path otherthan that through space.

leakage flux. The portion of the total magneticflux that does not link with all of the turns ofwire in a coil or transformer.

leakage inductance. The difference between thetotal inductance of a transformer winding andthat used in transferring energy from onewinding to another.

leakage radiation. Radiation from anything otherthan the intended radiating system.

leakage reactance. Opposition to alternating cur-rent offered by the leakage inductance of atransformer.

leakage resistance. The resistance of a path takenby leakage currents.

leaky. Having an abnormal resistance path sothat undesired current flows.

Lecher frame. An insulated, support along whichLecher wires are stretched.

Lecher oscillator. A device for producing a systemof standing waves along two parallel wirescalled Lecher wires used in measuring fre-quencies above 28 mc.

Lecher wires. Parallel wires coupled to a trans-mitter or receiver for measuring wavelength.The parallel wires form a transmission linealong which standing waves appear. The wave-length is equal to twice the distance betweenany two consecutive current nodes.

Leclanche cell. A primary cell having a carbonpositive electrode and a zinc negative electrodein an electrolyte of sal ammoniac and a de-polarizer. The common dry cell.

left-handed elliptically polarized wave. An ellip-tically polarized wave in which the rotation ofthe direction of displacement is counterclock-wise for an observer looking in the directionthe wave is traveling.

left-hand taper. Concentration of the resistancetoward the clockwise end of the range of apotentiometer or rheostat, held with the shaftpointing toward the observer.

leg. The part or parts of a filter or an attenuatorthat form a parallel branch across the circuit.

lens. A transparent object, usually glass, havingone or more curved surfaces designed tochange the direction of rays of light. Also, adevice for focuging radio waves. Also, anelectric or magnetic field used to focus theelectron stream in a cathode ray tube.

lens disc. A mechanical television scanning disc

in which each opening is fitted with a lens forthe purpose of securing greater brilliancy orlight concentration.

lens speed. A measure of the amount of light alens will pass, equal to focal length divided bydiameter.

lens turret. A rotating lens mount on a televisioncamera, to which are attached several lenses.It is used for rapidly switching lenses.

Lenz's law. An induced current always opposesthe current that produced it.

level. A value or amount, as of voltage or power.level indicator. A volume indicator.

light. Electromagnetic radiations having wave-lengths between 4000 and 7000 angstrom unitsand therefore visible to the eye.

light chopper. A mechanical device for interrupt-ing a light beam.

light flux. The total amount of light produced bya source, usually measured in lumens. Some-times used to describe invisible radiations suchas infra -red and ultra -violet rays.

Courtesy GELighthouse Tubes

lighthouse tube. (So called from its supposed re-semblance to the' shape of a lighthouse.) Asealed -disc triode in which the grid is a fiatwire mesh separated from flat cathode andplate surfaces by only a few thousandths ofan inch. Transit time is reduced, permittinguse at ultra -high frequencies.

light modulation. Variation in the intensity oflight, usually at audio frequencies, for com-munications or movie sound -track purposes.

lightning arrester. A protective device used toside-track lightning that strikes a receivingor transmitting antenna directly to ground.

lightning switch. A switch with large current -carrying capacity used to connect an antennato ground, when the antenna is not in use, forlightning protection.

light ray. The direction or path of propagationof light, represented by a straight line.

light relay. A photoelectric device in which achange in light intensity opens or closes a re-lay.

light-sensitive cell. A device whose electrical char-acteristics are changed when the amount oflight falling on it is changed.

light velocity. All electromagnetic radiations, in-cluding those of light, travel in space (in avacuum) with the same velocity, approximate-ly 186,000 miles per second or 300,000,000meters per second.

limit bridge. A Wheatstone bridge used for testingresistors. Conformity within tolerances,rather than exact resistance, is determined.

47

limiter. A device whose output is constant for allinputs above a critical value. scanning in which odd -numbered lines are

scanned as one field, and even -numbered linesare scanned as another field.

limiting. The act of removing amplitude varia-tions by a limiter.

line. One horizontal scan of the electron beam.Also, a transmission or power line.

linear. Having a straight-line characteristic.linear amplification. Amplification over a straight

portion of the characteristic curve.linear amplifier. A stage operated over the straight

portion of its characteristic curve. Specifical-ly, a transmitter stage used to amplify themodulated wave.

linear control. A volume or tone control havinguniform distribution of resistance along eachunit length of the resistance element.

linear detection. Detection in which the audio -frequency output is directly proportional tothe radio -frequency input for all normalsignals.

linear distortion. Distortion independent of theamplitude of voltage or current involved.

linearity. In television, the uniform distributionof picture elements along a line or over thetotal area of the image.

linearity control. In television, a control whoseadjustment makes the sweep more linear.

linearly polarized wave. A transverse wave inwhich the displacement has a constant direc-tion at a point in space.

linear power anplifier. A power amplifier in whichthe signal output voltage is directly propor-tional to the signal input voltage.

linear rectification. Rectification in which therectified current or voltage is proportional tothe amplitude of the input wave over a widerange of input amplitudes.

line -balance converter. A quarter -wave shield, usedat the end of a coaxial transmission line toraise the impedance of the outer conductor topermit connecting to a balanced transmissionline. A bazooka.

line cord. A two -wire cable terminating in a two -prong plug, used for making connection to anac or de wall outlet.

line -cord resistor. An asbestos -wrapped resistanceelement incorporated in a line cord for thepurpose of dropping the line voltage to theproper value for application to the series -con-nected tube filaments of a universal ac -dcreceiver.

line drop. The voltage drop between two pointson a power line or transmission line, due tothe resistance, reactance, or leakage of theline.

line equalizer. A part or parts inserted in a trans-mission line to correct the frequency -responsecharacteristic of the line.

line filter. A device containing one or more chokecoils and condensers, inserted between the linecord plug and the power line to block noisesignals.

line flyback. In a television system, the right -to -left return motion of the electron beam fromthe end of one line to the beginning of thenext. Also called horizontal flyback or hori-zontal retrace.

line -frequency blanking pulse. See horizontal blank-ing pulse.

line interlacing. In television, a system of picture

line microphone. A microphone made highly direc-tional by the use of a sound collector consist-ing of small tubes of different lengths placedflush with the microphone. A machine-gunmike.

line noise. Disturbing electrical pulses originatingin a transmission line.

line -of -sight distance. Straight-line distance fromstation to horizon. The transmitting range,under normal conditions, of high -frequencystations such as television, FM, and radar.

line -scanning frequency. The number of linesscanned each second, equal to the number ofscanning lines per frame, multiplied by theframe frequency.

line sequential. In color TV, a system in whicheach line in a field is scanned in a color dif-ferent from that of the line on either side ofit in that same field. Because of line inter-lacing, the intervening lines are scanned insucceeding fields, so that it requires six fieldsto scan each line in all the colors.

lines of force. Imaginary lines used to designatedirections in which electric or magnetic forcesact in space.

line -stabilized oscillator. An oscillator in which asection of transmission line is used as a sharp-ly selective frequency -controlling element.

line -synchronizing pulse. In television, the pulseadded to the video signal for the purpose ofcontrolling the horizontal sweep oscillator inthe receiver.

line voltage. The voltage existing at a wall outletor other terminals of a power line system.In most of the United States, between 110 and120 volts.

line -voltage regulator. A device that delivers anessentially constant voltage to the load, re-gardless of minor variations in the input Ivoltage.

link. The fusible and replaceable part used insome types of cartridge fuses. Also, a closedcircuit containing one or more coils used tocouple radio -frequency circuits. Also, a flatstrip serving as a removable connector be-tween two terminal screws.

linkage. Coupling together by lines of force thatpass through both parts.

link coupling. The coupling of two circuits by aclosed loop consisting of a few turns of wirecoupled to an inductance in each circuit, andconnected together by a pair of wires or alow -impedance concentric line.

lip microphone. A unidirectional microphone heldon the upper lip; used where outside noiselevel is extremely high.

Lissajous patterns. Patterns obtained when alter-nating voltages of various amplitude ratios,frequency ratios, and phase differences areplotted, mechanically traced, or applied toboth pairs of deflecting plates in a cathoderay tube.

literal number. A letter or symbol used for repre-senting quantities. Thus, R is a literal num-ber (sometimes called a general number)when used to represent resistance.

Litz wire. A special stranded wire made so thatevery strand is on the surface for the samedistance. Used to reduce the tendency ofhigh -frequency currents to flow near the sur-face of a conductor rather than through thecenter.

48

live. Having a voltage; energized.

live end. The part of a radio studio that gives thegreatest reflection of sound.

liven the studio. To remove sound -absorbing ma-terial from the studio, push back curtains toexpose window and wall surfaces, and set upsound -reflecting screens.

L network. A network composed of two im-pedance branches, one connected across thecircuit and the other in series with the cir-cuit, resembling in a schematic diagram theletter

load. That part or combination of parts intowhich power is fed to accomplish a desired re-sult. Also, the amount of power taken from acircuit.

loaded antenna. An antenna with extra inductanceor capacitance in series to increase its elec-trical length.

loaded Q. The Q of a resonant circuit when anexternal load is coupled to the circuit.

loading coil. A coil inserted in a circuit to in-crease its inductance but not to providecoupling with any other circuit.

load line. A line drawn on a graph of Ep-Ipcurves to show what the operating conditionswill be for a particular load in the tube platecircuit.

lobe. One of the loops in the radiation pattern ofan antenna.

lobe switching. Changing the direction in whichone or more of the antenna lobes point.

local control. Radio -transmitter control in whichthe control functions are performed directlyat the transmitter.

localizer. A transmitter in an instrument landingsystem used to lay out an approach course thatis a vertical plane perpendicular to the centerof the runway. Two signals are transmitted,which when received with equal strength indi-cate that the airplane is on the proper course.

local oscillator. The oscillator section of a super-heterodyne receiver.

locked groove. A blank, endless groove at the endof modulated grooves on a record, to preventfurther travel of the phonograph needle. Thisgroove is off -center on most modern phono-graph records, to provide an in -and -out mo-tion for actuating the tripping mechanism ofan automatic record changer, in which case itis more generally called the eccentric groove.

lockin. A term describing the condition thatexists when a sweep oscillator is in synchron-ism with the applied sync pulses. Also, a loctaltube.

locking relay. A relay that locks into positionwhen its coil is energized momentarily, thuseliminating the need of continual coil energiza-tion. A latching relay.

loctal tube. A tube with an 8 -pin base that islocked into its socket by a groove on thecentering key into which a spring ring in thesocket fits. Also called a lock -in or loktaltube.

lodestone. A mineral consisting chiefly of a mag-netic oxide of iron that is found in its naturalstate 'in a magnetized condition. Also calledmagnetite.

log. A list of radio stations. A record of stationswith which a radio transmitter has been incommunication; radio operators are requiredby law to keep this log. A detailed record de-

scribing the program being broadcast eachminute of the operating day by a broadcaststation. A record of the meter readings re-quired by law to be taken at regular intervalsin a broadcast transmitter and in certain othertypes of transmitters. Also, abbreviation forlogarithm.

log -1. Antilogarithm. To be read "A numberwhose log is."

logio. Logarithm of a number to the base 10,which is the common logarithm of a number.

loge. Logarithm of a number to the base E.which is 2.718 in the natural system oflogarithms.

logarithm. The common logarithm of a quantityis the exponent of the power to which thenumber 10 (the base of the common systemof logarithms) must be raised in order to equalthe quantity. Thus, 4 is the logarithm of10,000 (log 10,000 = 4) because 104 is equal to10,000. In the natural system of logarithms,the base is 2.718, which is designated by theGreek letter E.

logarithmic horn. A horn whose diameter varieswith its length according to a logarithmic law.

logarithmic scale. A scale for graphs, on whichdistances from zero of the scale are propor-tional to the logarithms of the numbers withwhich these points on the scale are labeled.

logging. Making a record of the exact dial set-ting at which a station is received, or makinga written record of any other essential data.

loktal tube. See loctal tube.longitude. The distance east or west from a

meridian passing through Greenwich, Eng-land, measured in degrees, minutes, and sec-onds.

longitudinal waves. Sound, pressure, and someseismic waves, transmitted through a materialmedium in which the individual particles ofthe medium move back and forth in the direc-tion in which the wave progresses. The me-dium undergoes condensations and rarefac-tions. Radio waves are not longitudinal, buttransverse.

long waves. Wavelengths longer than the longestbroadcast band wavelength of 545 meters. Longwaves correspond to frequencies between about15 kilocycles and 550 kilocycles.

long-wire antenna. An antenna whose length is anintegral multiple of a half -wavelength. A har-monic antenna.

loop. A closed circuit or path. Also, on a graph,the plot of a variable that forms a hump orclosed, curved pattern. Also, another name forantinode.

loop antenna. An antenna consisting of one ormore complete turns of wire.

loose coupling. Very little coupling between twocoils, so that only a small part of the mag-netic flux of one coil links with the other coil.

loran. (Coined from LOng RAnge Navigation.)A system for determining direction and posi-tion in which signals from two synchronouslyoperated stations are received and the timedifference between their signals is determined.From specially prepared charts this time dif-ference is converted into positional informa-tion.

loss. -Energy dissipated before it accomplishesuseful work.

loudness. The intensity of sound.

loudness level. See equivalent loudness level.

49

Courtesy Jensen

Loudspeaker (Exploded View)

loudspeaker. A device for converting electricenergy into acoustic energy.

louver. A loudspeaker grille construction inwhich sloping slats of a cabinet hide the loud-speaker yet allow sound waves to emerge un-hindered. Also, a similar construction forventilating or decorative purposes. Sometimesspelled louvre.

low -frequency padder. In a superheterodyne re-ceiver, a semi -adjustable condenser placed inseries with the oscillator tuning circuit to ad-just the calibration of the circuit at the low -frequency end of the tuning range.

low-level modulation. Modulation at a point in atransmitter where the power level is low com-pared to that at the output of the transmitter.

low -loss construction. The use of materials or themanner of constructing parts so that there isa minimum of loss.

low-pass filter. A filter network designed to passall frequencies below a cut-off frequency value,while attenuating or rejecting higher fre-quencies.

low tension. Low voltage.L pad. An attenuation network having its ele-

ments arranged to resemble the letter L.lug. A small strip of metal used as a terminal to

provide a convenient means for making asoldered connection.

lumen. A unit of light flux. A light source of onecandle power emits 12.56 lumens of light.

luminescence. Radiation of light by an object thathas previously been exposed to strong light.Emission of light not directly due to heat.

luminous intensity. The candlepower of a source oflight.

lumped capacitance. Capacity concentrated in acomponent, as distinguished from stray ordistributed capacity.

lumped constant. A single constant, equivalentelectrically to all the distributed constants ofthat type that exist in a circuit.

lumped impedance. Impedance concentrated in acomponent, as distinguished from stray or dis-tributed effects.

lumped inductance. Inductance concentrated in acomponent, as distinguished from stray or dis-tributed inductance.

lumped resistance. Resistance concentrated in acomponent, as distinguished from stray ordistributed resistance.

Mmagic eye. See electron -ray tuning indicator.

magnal base. An 11 -pin base used for cathoderay tubes.

magnesium copper -sulphide rectifier. A dry -disc rec-tifier consisting of magnesium in contact withcopper sulphide.

magnet. A substance or device that attracts otherpieces of magnetic material and attracts orrepels other magnets. A permanent magnethas' this property indefinitely; an electromag-net only when current is flowing through itscoil.

magnet gap. The space between the pole faces ofa magnet.

magnetic. Pertaining to a magnetized substance,or to a substance capable of being magnetized.

magnetic cartridge. A case or shell containing anelectromagnetic device used in a phonographpickup for converting mechanical movementof the needle into electric energy.

magnetic circuit. A complete path for magneticlines of force.

magnetic contactor. A magnetically actuated de-vice for opening or closing an electric powercircuit.

magnetic cycle. One complete round of changesin the magnetization of an object, correspond-ing to one cycle of the alternating current pro-ducing the magnetization.

magnetic damping. Reduction or elimination ofoscillation or vibration by the opposing forceproduced by eddy currents.

magnetic deflection. A method of bending the elec-tron stream in a cathode ray tube by meansof the magnetic field produced by coils placedaround the tube.

magnetic density. The number of magnetic linesof force per unit cross-sectional area.

magnetic field. The space around a permanentmagnet or a current -carrying conductor or coilwhere magnetic flux exists.

magnetic field intensity. Magnetizing force or mag-netic force.

magnetic figures. A pattern showing the distribu-tion of a magnetic field, made by sprinklingiron filings on a non-magnetic surface in thefield.

magnetic flux. Magnetic lines of force.magnetic flux density. The number of magnetic

lines of force per square unit of area.magnetic focusing. Focusing of an electron beam

in a cathode ray tube by the action of a mag-netic field.

magnetic keeper. A bar of soft iron placed acrossthe poles of a permanent horseshoe magnet tocomplete the magnetic circuit when the mag-net is not in use, to prevent demagnetization.

magnetic leakage. Passage of magnetic flux out-side of the path along which it can do usefulwork.

magnetic lines of force. Imaginary lines alongwhich magnetic forces are acting in a magneticfield.

magnetic loudspeaker. A loudspeaker consistingessentially of a permanent magnet, a pivotedarmature mechanically connected to the dia-phragm or cone, and a coil connected to theoutput stage of a radio receiver or other ap-paratus. Interaction between the permanentmagnetic field and that developed in thearmature by the coil results in movement ofthe armature and production of sound wavesby the diaphragm.

50

magnetic microphone. A microphone in which theoutput voltage depends upon variations in thereluctance of a magnetic circuit.

magnetic pickup. A phonograph pickup contain-ing a permanent magnet, one or two coils, aniron armature, and a core structure so ar-ranged that movement of the phonographneedle in the record groove varies the amountof magnetic flux passing through the coils,thereby inducing audio -frequency voltages inthe coils.

magnetic poles. Regions in a magnet near whichthe field is concentrated.

magnetic pole strength. Force exerted on a metal-lic object by a magnetic pole, measured inunit poles. A unit pole is one that repels asimilar pole at a distance of one centimeterwith a force of one dyne.

magnetics. The branch of science that deals withthe laws of magnetic phenomena.

magnetic saturation. A condition of an iron corein which further increases in magnetizing forceproduce little increase in magnetic flux.

magnetic sensitivity. The amount of deflection ofthe electron stream in a cathode ray tube pro-duced by a stated current through the deflec-tion coil.

magnetic shield. An iron housing used with aradio part to prevent external magnetic fieldsfrom affecting the part, or to prevent mag-netic fields produced by the part from affect-ing other circuits and parts.

magnetic storm. A rapid and violent fluctuationin the intensity of the earth's magnetic field,disrupting radio and telegraphic communica-tions.

magnetic vane meter. An ac meter containing ametal vane pivoted inside a coil. The vane ismagnetized by the coil's magnetic field withsuch polarity that the vane and attached point-er are caused to rotate to a position that in-dicates the strength of the alternating currentflowing through the meter coil.

magnetism. The ability to attract magnetic ma-terials and to influence moving electrons.

magnetite. Lodestone.magnetization curve. A curve showing the relation

between the magnetizing force H (ampere -turns or gilberts per cm) and the flux densityB (lines per sq centimeter). Also called B -I -Icurve.

magnetizing force. See magnetomotive force.magnetomotive force. The force that produces

magnetic flux in a magnetic circuit. Thatwhich sets up and maintains a magnetic field.

magnetosfriction. The slight change in the size ofmaterial when it is magnetized.

magnetostriction oscillator. An oscillator in whichthe grid and plate circuits are coupled througha rod of magnetic material. The alternate ex-pansion and contraction of the rod withchanges in plate current governs the funda-mental frequency of the oscillator.

magnetostrictive. Changing in size (dimensions)when placed in a magnetic field.

magnetron. A tube in which the electron flowfrom a cathode to one or more anodes is in-fluenced by an external magnetic field, andthe electric field produced by the anode volt-ages.

magnetron oscillator. An oscillator using a mag-netron, most generally one in which the tubecontains cavities that are the circuit com-ponents.

magnet wire. Insulated copper wire in sizes com-monly used for winding coils in electromag-netic devices.

magnitude. The amount or value of a quantity.mains. Ordinary power lines.

major lobe. The loop in the radiation pattern ofan antenna that is the path of maximumradiation.

manganin. A metal alloy commonly used in rheo-stats and resistors, because it is not appreci-ably affected by changes in temperature.

man-made static. High -frequency noise signalsproduced by sparking in electrical apparatusor power lines and picked up by receivers.

manometer. A pressure -measuring gauge.mantissa. The part of a logarithm to the right of

the decimal point. It is always a decimal andalways positive. Example: In log 4612.6637, the mantissa is .6637.

manual tuning. Tuning a receiver to a desiredstation by rotating the tuning -control knob byhand.

Marconi antenna. An antenna directly connectedto ground or close enough to ground so thatthe ground plays an essential part in theradiation of energy.

marker. See radio marker beacon. Also, a bearingor range indication on a radar screen.

marker pip. A frequency index mark used incathode ray oscilloscope alignment of TV setsand in conjunction with a sweep -driven signalgenerator. The marker pip is produced bycoupling a fixed -frequency oscillator to theoutput of the signal generator.

marking wave. In telegraphic communication, thewave on which the code characters are beingtransmitted.

mask. A plastic, metal, or wood covering used toconceal those portions of a picture tube facenot being used for reproduction of the image.

masking. The shift of the threshold of audibilityof a sound because of the presence of anothersound.

masking disc. A baffle used in an electron gun torestrict the cone of electrons to a small sizeto prevent spherical aberration.

Magnetron

CourtesyRaytheon MID. Co.

Masonite. Fiberboard thatexploded under steamhard sheets.

mass. The property of athe acceleration it willby a given force.

consists of wood fibersand compressed into

body that determineshave when acted upon

51

mast. A vertical pole or structure supporting anantenna.

master. The negative die made from an originalwax recording, which is used to produce otherdies, from which are made the stamping diesused to produce phonograph records.

master control board. The panel on which all themain operating controls of a broadcast studioor transmitter are located.

master oscillator. The oscillator that establishesthe carrier frequency of a transmitter.

master -oscillator power -amplifier. A combinationof a vacuum -tube oscillator followed by a

radio -frequency amplifier stage.matched load. A load whose impedance exactly

equals the impedance of the source.matching. Connecting two circuits or parts to-

gether in such a way that their impedancesare equal.

matching stub. Two wires or a section of trans-mission line of such a length that, when prop-erly tapped, or when connected to the properpoint along a transmission line, will match theimpedances of the load and source.

matching transformer. A transformer for matchingtwo or more impedances.

matrix. A negative from which duplicate phono-graph records are molded.

matter. Anything that occupies space.

maximum. Greatest quantity or amount of any-thing.

maximum available power. The power any devicecan deliver when its source and load imped-ances are matched.

maximum output. The greatest output power thatcan occur regardless of distortion.

maximum rated carrier power. The greatest powerat which a transmitter can be operated satis-factorily or safely.

maximum undistorted output. The maximum audiopower output a receiver or audio amplifierwill deliver without having more than a statedamount of total harmonic distortion.

maximum usable frequency. The highest frequencythat can be used for reliable radio transmis-sion at a specified time between two pointson the earth by reflection from the regularionized layers of the ionosphere.

maxwell. The unit of magnetic flux, equal to onemagnetic line of force.

MAYDAY. The international distress call forradiotelephone communication. It is thephonetic spelling of the French "M'aider,"meaning "Help me."

M -derived filter. A filter with infinite attenuationat some specific frequency, producing asharper cut-off than can be obtained from astandard filter.

mean carrier frequency. The resting frequency orassigned carrier frequency of a frequency -modulation transmission system.

mechanical bandspread. The use of a vernier tun-ing dial to make a gang tuning condenser ro-tate more slowly than is possible with theregular tuning -control knob, making stationtuning easier in crowded short-wave bands.

mechanical damping. The use of rubber or plasticblocks with the moving parts of a record-ing cutter or reproducer to absorb undesiredvibrations.

mechanical rectifier. A vibrator.

mechanical scanning. Breaking down an imageinto a number of picture elements by mechan-ical means such as a Nipkow disc.

mechanical television. Any television system inwhich the scene to be transmitted is brokenup into picture elements, and reconstructedat the receiving end by a mechanical devicesuch as a rotating scanning disc.

megacycle (mc). One million cycles per second.megatron. See lighthouse tube.

megger. A high -range ohmmeter used for measur-ing leakage resistances and insulation resist-ances.

megohm (meg). One million ohms.

Meissner oscillator. An oscillator in which thegrid and plate circuits are inductively coupledthrough an independent tank circuit that de-termines the frequency.

mercury. A heavy, silver -colored metal that isliquid at ordinary room temperatures. Whenheated, it gives off a vapor that is highly con-ductive when ionized.

mercury barometer. An instrument in which thepressure of the atmosphere is indicated bythe height of a column of mercury.

mercury switch. An electric switch made by plac-ing a large globule of mercury in a glass tubehaving electrodes arranged in such a way thattilting the tube will cause the mercury tomove and make or break the circuit.

mercury-vapor tube. A tube containing a smallamount of mercury, which is ionized. The re-sulting ionization of the mercury-vapor mole-cules gives a high plate current.

meridian. A great circle on the face of the earth,passing through both poles.

Mershon condenser. An early wet -electrolytic con-denser.

meson. A particle having a unit charge like anelectron but a mass in between that of elec-trons and protons. Also called heavy electron,barytron, mesotron, penetron, X particle, etc.

metal detector. An electronic deirice for locatingmetal objects.

metallic insulator. A shorted quarter -wave sectionof a microwave transmission line that actsas an electrical insulator at the frequency forwhich its length is one quarter wavelength.

metallized resistor. A resistor made by depositinga thin film of high -resistance metal on thesurface of a tube or rod made of glass or otherinsulating material.

metal tube. A vacuum tube having a metal enve-lope instead of a glass envelope. Electrodeconnections are made through glass beadsfused into the top and the bottom of the metalenvelope.

meteorograph. An apparatus for recording simul-taneously several meteorologic phenomena,such as temperature, moisture, etc.

meter. The unit of length in the metric system.One meter is equal to 3.28 feet. Also an instru-ment used for making electrical measure-ments. A voltmeter measures voltage; an am-meter or milliammeter measures current; awattmeter measures power; an ohmmetermeasures resistance.

metric system. A decimal system of measures andweights, using the meter and the gram as basic

52

units. The system of units based on metersfor length, grams for mass.

mho. The unit of conductance, which is the recip-rocal of resistance.

mica. A transparent flaky mineral that splitsreadily into thin sheets and has excellent in-sulating and heat -resisting qualities, used ex-tensively to separate the plates of condensers,to insulate electrode elements of vacuum tubes.and for other insulating purposes in radioapparatus.

mica condenser. A condenser using sheets of micaas the dielectric material that insulates ad-jacent plates from each other.

Micarta. An insulating material made by com-pressing mica and a binding material such asBakelite.

micro. Prefix meaning one millionth of. Abbre-viated µ (Greek letter mu) or m.

microammeter. A meter designed to measure ex-tremely small currents.

microampere (pa). A unit of current, one mil-lionth of an ampere.

microfarad (mfd). A unit of capacity, one mil-lionth of a farad.

microhenry. A unit of inductance, one millionthof a henry.

micromho. A unit of conductance, one millionthof a mho.

micromicro. A prefix meaning one millionth ofone millionth of. Abbreviated no, (the Greekletter mu) or mm.

micromicrofarad (mmf). A unit of capacity, onemillionth of a microfarad.

micron. A unit used to express wavelengths oflight. One micron is equal to 10,000 angstromunits or .0001 cm.

Courtesy The Turner Co.Microphones

microphone. A deviceinto correspondingenergy. It containsphragm that moveswave variations to

that converts sound wavesaudio -frequency electricalsome form of flexible dia-in accordance with sound -generate a voltage.

microphone adapter. A device that slips under atube or is otherwise connected to a radio re-ceiver, providing terminals to which a micro-phone can be connected to convert the re-ceiver into a public-address system.

microphone button. A button -shaped containerfilled with carbon particles. When attachedto the diaphragm of a microphone, the resist-ance between the terminals of the buttonvaries in accordance with movements of thediaphragm.

microphone cable. The group of wires connectinga microphone to an amplifier or mixer.

microphone preamplifier. An audio amplifier thatamplifies the output of a microphone so thatthe audio signal can be sent over a transmis-sion line to the main amplifier.

microphone stand. 'A table or floor stand used tosupport a microphone in a desired position.

microphone transformer. The iron -core of trans-former that couples the microphone to a micro-phone amplifier, to a transmission line, or tothe input circuit of the main audio amplifier.

microphonic. A condition in which mechanicalmovement of some radio part other than amicrophone causes variations in circuit cur-rent.

microsecond. One millionth of a second.microswitch. A switch in which a very small

movement of its actuating plunger suffices tochange the switch from on to off or vice versa.

microvolt. One millionth of a volt.microvoltmeter. A highly sensitive voltmeter that

indicates differences of potential in micro-volts.

microvolts per meter. A measure of radio fieldintensity, equal to the signal strength at theantenna in microvolts divided by the effectiveheight of the antenna in meters.

microwave. A very short electromagnetic wave,having a wavelength less than one meter.

microwave oscillator. An oscillator that generatesa frequency higher than 300 megacycles (lessthan one meter).

microwave relays. A system of increasing therange of television coverage by reception andrebroadcast of the signal over a chain of tow-ers located 10 to 25 miles apart. Each towercontains a receiver to pick up the signal anda transmitter to rebroadcast it, operating inthe part of the microwave region from 3000to 30,000 mc.

mike. Microphone.

mil. A unit of measurement equal to one thou-sandth of an inch (.001 inch).

mil -foot. A wire one foot long having a diameterof one mil.

Miller effect. The reflection across the input ofthe grid -plate capacity increased by a factordetermined by the stage gain and the phaseangle of the load voltage with respect to theequivalent ac plate voltage.

milli. Prefix meaning one thousandth of. Ab-breviated m or k.

milliammeter. A meter that indicates current flowin milliamperes.

milliampere (ma). A unit of current, one thou-sandth of an ampere.

millihenry. A unit of inductance, one thousandthof a henry.

millimeter. A metric unit of length, one thou-sandth of a meter. One millimeter is approx-imately equal to one twenty-fifth of an inch.

millimicron. A unit of length, one thousandth ofa micron, or one millionth of a millimeter.

millivolt. A unit of voltage, one thousandth of avolt.

milliyoltmeter. A voltmeter that indicates voltagein millivolts.

milliwatt. A unit of power equal to one thou-sandth of a watt.

53

minimum. Lowest, least, or smallest quantity ofanything.

minor lobe. Any lobe except the major lobe in aradiation pattern of an antenna.

minus sign. A sign (-) used in mathematics toindicate subtraction or a negative value. Usedin radio to indicate the negative terminal ofa voltage source, or negative polarity.

minute. One -sixtieth part of a degree. One com-plete revolution of an angle -generating line is360°, which is 360 X 60 or 21,600 minutes.

mismatch. The condition in .which the impedanceof a source does not match or equal the im-pedance of the connected load.

mixed -high frequencies. The part of the televisioncolor signal that carries the finer details (highfrequencies) of the transmitted image.

mixer. A control that permits combining the- out-put signals of two or more af signal sourcesin any desired proportion before these signalsare fed to the input of the main af amplifier.Also, popularly, a mixer -first detector.

mixer -first detector. The stage in a superhetero-dyne receiver in which the incoming modulatedrf signals are combined with the local oscilla-tor signals to produce the i-f signal.

mixing. Feeding two or more signals to the samecircuit.

mobile receiver. A receiver designed to be op-erated while in motion.

mobile station. A radio station operated from amovable location such as an automobile, firetruck, train, ship, or airplane.

mobile transmitter. A transmitter designed to beoperated while in motion and normally sooperated.

mode. One of the methods of operation of amicrowave system that will produce usablesignals.

mode number. The number of whole cycles duringwhich a mean -speed electron remains in thedrift space of a reflex klystron.

modulate. To vary the amplitude, frequency, orphase of a signal.

modulated amplifier. See modulated stage.modulated continuous wave (mew). In telegraphy,

emission in which the carrier is modulated bya constant audio -frequency tone.

modulated stage. A transmitter stage in which thefrequency, phase, or amplitude of a signal tobe modulated is changed in accordance withthe modulating signal.

modulated wave. A radio wave that varies eitherin frequency, in phase, or in amplitude in ac-cordance with the wave form of the intelli-gence signal being transmitted.

modulating electrode. An electrode used in acathode-ray tube to control the beam current.

modulating wave. The af signal, picture signal,facsimile signal, or code signal that is madeto modulate the carrier wave of a transmitter.

modulation. Changing the amplitude, phase, orfrequency of one wave in accordance with somecharacteristic of another wave. In amplitudemodulation, the amplitude of the modulatedwave varies in step with the amplitude varia-tions in the modulating wave at a rate deter-mined by the frequency of the modulatingwave. In phase modulation, the phase of suc-cessive peaks of the modulated wave varies instep with the amplitude variation of the mod-ulating wave at a rate determined by the fre-

quency of the modulating wave. In frequencymodulation, the frequency of the modulatedwave varies in step with the amplitude varia-tions of the modulating wave at a rate deter-mined by the frequency of the modulatingwave.

modulation' capability. The maximum percentagemodulation that is possible without objection-able distortion.

modulation distortion. Distortion of wave formdue to a greater plate -current change on onehalf -cycle than on the other half -cycle.

modulation envelope. A curve drawn through thepeaks of a graph showing the wave form of amodulated rf carrier signal.

modulation factor. The ratio of the maximumamplitude of the modulation envelope to theamplitude of the unmodulated carrier. Multi-plying this factor by 100 gives the percentageof modulation.

modulation grid. An electrode used between thecathode and focusing electrodes in a cathode-ray tube to control the amount of emission andthereby the brilliance of the spot.

modulation index. See modulation factor.modulation monitor. An instrument used to pro-

vide a continuous indication of the modulationpercentage at a transmitter.

modulation percentage. The ratio of the modu-lating voltage to carrier voltage, expressed inper cent.

modulator. A transmitter stage that supplies themodulating signal.

molded condenser. A condenser cast in Bakeliteor other insulating material to keep out dustand moisture.

molecular theory of magnetism. The theory thattreats each molecule of matter as a completepermanent magnet. When a piece of materialis magnetized, all the molecular magnets lineup with like poles pointing in the same direc-tion.

molecule. The atom or group of atoms that con-stitutes the smallest particle in which a com-pound or material can exist separately.

molybdenum. A metallic element of the chromiumgroup used in the manufacture of tubes.

monitor. A person who checks the quality of aradio or television program at the studio ortransmitter. Also, a receiver used in check-ing or monitoring programs.

monitoring. The act of listening to or observinga program either during rehearsals or actualbroadcasts, to check quality and set the levelsfor proper sound or visual effects.

monitor oscilloscope. An oscilloscope whose timebase is permanently set at line or frame fre-quency, or a sub -multiple of either, for con-tinuous indication of the video voltages of atransmission.

monitor panel. A group of controls used to gov-ern the level of sound signals from a studio,or of television video signals.

monkey chatter. Garbled speech or music heardalong with a program, occurring when theside frequencies of an adjacent -channel stationbeat with the desired station signal.

monochromatic. Of or pertaining to one coloronly.

monoscope. A cathode-ray tube that producesfixed television picture signals correspondingto the design or picture that has been printedon its screen.

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Monoscope

monotron. A monoscope.

Morse Code. A system of dot and dash signalsused in the transmission of messages by radioor wire telegraphy. The International MorseCode is used universally for radiotelegraphy,and the American Morse Code is used only forwire telegraphy in the United States.

Morse sounder. A telegraph receiving instrumentthat produces an audible sound at the begin-ning and end of each dot and dash. From thesesounds a trained operator can read the mes-sage.

mosaic. The light-sensitive surface of an icono-scope, consisting of millions of tiny silverglobules on a sheet of ruby mica, each globuletreated with caesium vapor to make it photo-sensitive.

mother. A positive recording produced directlyfrom the metal master or negative.

motion -picture pickup. Use of a television camerato pick up scenes directly from motion -pic-ture film.

motor. A machine that converts electrical energyinto mechanical energy. It consists essentiallyof a large number of conductors mounted onan armature that rotates in a magnetic field.

motorboafing. Regeneration occurring at a lowaudio frequency in a radio receiver or audioamplifier, resulting in putt -putt -putt soundsresembling those made by a motorboat.

motor -generator. An electric motor directly con-nected to one or more generators for the pur-pose of converting one voltage to another volt-age or frequency.

mouth. The large end of a horn loudspeaker.moving -coil instrument. Any instrument in which

the moving system is a coil that carries thepointer or mirror or other indicating device.

moving -coil loudspeaker. A loudspeaker in whichthe mechanical forces acting on the diaphragmare produced by interaction between the mag-netic field of the moving conductors (voicecoil) and the steady applied magnetic fieldproduced by a field coil or permanent magnet.

moving -coil meter. See moving -coil instrument.moving -coil microphone. A moving -conductor

microphone in which the conductor is a coillocated in a strong magnetic field produced bya permanent magnet. A dynamic microphone.

moving -conductor microphone. A general term ap-plying to all microphones in which the out-put voltage depends upon motion of a con-ductor in a magnetic field.

Moving Target Indicator (MT!). An electronic de-vice that will permit only moving targets toshow on a radar scope.

mu factor. The ratio of the change in one elec-trode voltage to the change in another elec-trode voltage when the current and all otherelectrode voltages are maintained constant.For example, the amplification factor.

multi -band antenna. An antenna that can be usedwith satisfactory results on a number of fre-quency bands.

multi -channel transmitter. A transmitter havingtwo or more complete radio -frequency sec-tions capable of operating on different fre-quencies either individually or simultaneously.

multielectrode tube. A vacuum tube having morethan three electrodes associated with a singleelectron stream.

multi -frequency transmitter. A radio transmittercapable of operating on two or more select-able frequencies, one at a time, using presetadjustments.

multigrid tube. A vacuum tube having more thanone grid electrode.

muitimeter. A test instrument having provisionsfor measuring voltages, currents, and resist-ance.

multipath reception. The reception of a directwave from the transmitter accompanied byone of more reflected waves. See ghost andecho.

multiple connection. The connecting of two ormore devices in parallel.

multiple -contact switch. A switch in which themovable contact can be set to any one of anumber of different fixed contacts.

multiple modulation. Modulation in which a car-rier wave of one frequency is modulated byan intelligence signal, and the resultant waveis then made to modulate a second carrier wavehaving a second frequency, etc.

multiple scanning. The process of scanning animage in two or more individual fields, eachcontaining a fraction of the total picture in-formation. Interlaced scanning.

multiple -tuned antenna. An antenna connected toground through tuning coils or condensers atmore than one point, so that the total of thereactance in parallel will make the antennaresonant at the desired frequency.

multiple -unit tube. A vacuum tube having two ormore groups of electrodes in a single envelope,each with its own electron stream.

multiplex operation. Simultaneous transmission oftwo or more messages in either or both direc-tions over the same transmission path in atelegraph system.

multiplex radio transmission. The simultaneoustransmission of two or more signals using acommon carrier wave.

multiplication. The process of determining by abriefer computation the result of adding anygiven number or quantity a certain number oftimes. Thus, 3 x 4 is 4 added together 3 times,or 4 + 4 + 4. Multiplication is indioated bythe sign X. In algebra, the multiplication signis usually omitted between general numbers(numbers expressed by letters), or the sym-bol is used to denote multiplication. Exam-ples: I X R, IR, and FR all mean that I isto be multiplied by R; 2srfL means 2 timesr times f times L. In algebra, the productof two numbers having like signs is positive.The product of two numbers having unlikesigns is negative.

55

multiplier. A resistor used in series with a volt-meter to increase the range of the meter.

multiplier tube. A tube in which emitted electronsare pulled along by increasingly higher po-tentials and are made to strike a number ofplates (called dynodes) successively. At eachplate, secondary emission occurs, resulting ina high current from the last plate and givingthe effect of high gain.

multipolar. Having more than one pair of mag-netic poles.

multivibrator. A relaxation oscillator consistingof two tubes connected so that energy fromthe plate circuits is fed to the opposite gridcircuits at the proper time and in the properphase to produce the desired output signal.

muting. Silencing, or reducing in volume.muting switch. Device used in automatic -tuning

systems to silence the audio system while sta-tions are being selected or tuned in.

mutual conductance. The ratio of the change inplate current to the change in grid potentialproducing it, under the condition of constantplate voltage. See transconductance.

mutual inductance. The common property of twoassociated coils or electric circuits that deter-mines how much electromotive force will beinduced in one by a change of current in theother. Mutual inductance is measured inhenrys, and is designated by the letter M.

mutual induction. The generation of a voltagein one circuit by the varying current in an-other circuit when inductive coupling exists.

Mycalex. A hard, molded insulating materialconsisting chiefly of ground mica and leadborate.

NNational Electric Code. A set of rules governing

construction and installation of electrical ap-paratus, as approved by the National Boardof Fire Underwriters.

natural frequency. The fundamental resonant fre-quency of a coil -condenser circuit, not a har-monic frequency.

natural frequency of an antenna. The fundamentalresonant frequency of an antenna alone (with-out added inductance or capacity).

natural wavelength. The wavelength correspond-ing to the natural frequency of a circuit.

nautical mile. The length of a minute along agreat circle on the earth. A U. S. land mileis .8684 of a nautical mile.

needle. The part of a phonograph pickup thatconverts the variations in the record groovesinto mechanical movements, which are in turnconverted into audio frequency signals.

needle pressure. Effective weight of the tone armand pickup on the phonograph record at thepoint of contact (needle point).

needle scratch. Noise components in the output ofa phonograph pickup due to the friction ofthe needle riding in the groove.

needle talk. Sounds produced by vibrations ofthe phonograph needle and/or other associatedparts of a phono pickup, heard directly fromthe pickup, not through the amplifier. Alsocalled needle chatter.

negative. Having more electrons than normal, ormore than some reference point. Also, in thenumerical scale, a number below zero.

negative bias. A voltage that makes the controlgrid of a radio tube negative with respect tothe cathode.

n egative charge. More than the normal numberof electrons.

negative feedback. Degeneration, which decreasesthe amplification. Also called inverse feed-back or stabilized feedback.

negative ghosts. Duplicate images that appearon a television screen with intensity varia-tions opposite to those of the picture.

negative image. A reversed television image inwhich the dark portions of the televised sceneappear bright, and the bright portions dark.

n egative modulation. In television, a method oftransmission in which a decrease in scene il-lumination causes an increase in the radiatedpower of the transmitter. In an AM facsimilesystem, that form of modulation in which themaximum transmitted power corresponds tothe maximum density of the subject copy. Inan FM facsimile system, the form of modula-tion in which the highest transmitter frequencycorresponds to the maximum density of thesubject copy.

negative picture phase. A condition wherein in-creases in brilliancy make the television pic-ture signal voltage swing in a negative direc-tion.

negative resistance. A characteristic of an electricarc, or, to a limited degree, of vacuum tubes,wherein an increase in voltage produces a de-crease in current.

negative -resistance oscillator. A tube operated onits negative resistance characteristic so that itdelivers energy to a tank circuit to produceoscillation.

negative terminal. A terminal having more thanthe normal number of electrons, or one havingmore electrons than another to which it is be-ing compared.

negative transmission. The transmission of tele-vision signals in such a way that a decreasein initial light intensity causes an increase inthe transmitted power.

neon. A gas used in electronic tubes. It producesa characteristic red glow when ionized.

neon glow lamp. A neon -filled gaseous tube havinga glass envelope through which can be seenthe characteristic red glow of neon whenionization occurs during operation of the tube.

neon oscillator. A relaxation oscillator using aneon glow lamp instead of a vacuum tube todischarge the condenser.

neper. A unit of power gain or loss using thenatural system of logarithms as its base, re-placed by the decibel and volume unit.

network. Any complex electrical circuit. Also,a group of broadcasting stations connected to-gether -by radio or wire telephone lines so thatall stations can broadcast a program originat-ing at one of the stations.

neutral. An object that has its normal numberof electrons and therefore is uncharged elec-trically.

neutralization. Any process that balances out orprevents an undesirable effect. Specifically,preventing oscillation in an amplifier by in-troducing a voltage into the input equal inmagnitude but opposite in phase to the feed-back through the interelectrode capacitance.

neutralizing condenser. A variable condenser usedin transmitting and receiving circuits to feeda portion of the ac plate voltage back to thegrid circuit for neutralizing purposes.

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neutralizing indicator. A device for indicating thedegree of neutralization of an amplifier.

neutralizing tool. See aligning tool.

neutralizing voltage. The ac voltage fed from thegrid circuit to the plate circuit (or vice versa),deliberately made 180° out of phase with andequal in amplitude to the ac voltage trans-ferred through undesired paths, usually thegrid -plate tube capacitance.

neutral wire. The middle wire of a three -wire,two-phase power line, usually grounded.

neutrodyne circuit. A circuit in which a portionof the rf plate voltage is fed back into thegrid circuit 180° out of phase to reduce thetendency toward oscillation.

neutron. An electrically neutral particle havingabout the same mass as a proton.

Nichrome. An alloy of nickel, iron, and chromiumthat has a high resistance per volume unit andis capable of withstanding high temperatures.

Nicol prism. Two prims of Iceland Spar crystalcemented together with Canada balsam, usedto polarize light.

night errors. Errors introduced by variations interrain, time of day, season of year, differenttransmission characteristics, etc., that affectbearings taken with loop antennas of radiodirection finders.

Nipkow disc. A flat round plate having one ormore spirals of holes around the outer edge,used in mechanical television scanning.

noctovision. A television system using opticallyinvisible rays, usually infra -red, for scanningpurposes at the transmitter.

nodal point keying. A method of keying an arctransmitter in which the transmitting keyconnects to a point in the antenna circuit thatis essentially at ground potential at all times.

node. Any point, line, or surface that has zeroamplitude.

noise. Any unwanted sounds or electrical dis-turbance interfering with the desired program.In television, an interfering voltage producinga grainy or streaked picture.

noise filter. A device inserted between a walloutlet and the power cord plug of a receiverto block noise interference that might other-wise enter the receiver. Noise filters are alsoplaced between the power line and the deviceproducing the noise, to prevent escape of thenoise signals into the power line.

noise level. The strength of noise signals in acircuit, or of acoustic noise in a particularlocation.

noise limiter. A circuit that limits the effects ofinterfering noises by cutting off all noise peaksstronger than the highest signal peak beingreceived.

noise -reducing antenna system. An antenna systemin which the only part capable of picking upsignals is the antenna proper, this beingerected high enough to be out of the noise -interference zone. The lead-in is a shieldedcable of twisted two -wire line that can passthrough the interference zone without pickingup noise signals.

noise silencer. See squelch circuit.nomograph. A chart or graph containing a series

of scales on which equations can be solved byplacing a ruler on two known values and read-ing the answer where the ruler intersects thescale for the unknown value. Also known as anomogram.

non-conductor. Any material that offers very highopposition to the flow of electricity. An insu-lating material.

non -corrosive flux. Flux that is free from acid andother substances that might cause corrosion.

non -homing tuning system. A motor -driven auto-matic tuning system in which the directionof motor rotation is reversed at the ends ofthe tuning range. When a station -selectingbutton is pressed, the motor will rotate in thedirection in which it was last rotating. If thedial setting for the desired station is in theother direction, the motor will rotate the tun-ing mechanism to the end of the scale andwill then reverse and proceed to tune the re-ceiver to the desired station frequency.

non -inductive circuit. A circuit having practicallyno inductance.

non -inductive condenser. A condenser having prac-tically no inductance. The layers of foil andpaper are staggered in winding so that onelayer of foil protrudes at one end, and theother layer protrudes at the other end, so theleads make contact to the entire edge of thefoil strips rather than just one end.

non -inductive load. A load having practically noinductance.

non -inductive resistor. A wire -wound resistor soconstructed that the wire coil has practicallyno inductance. Used at high frequencies.

non -inductive winding. A method of winding sothat the magnetic field about a turn cancelsthe field produced about the next adjacentturn. Used in making non -inductive resistors.

non-linear. Not proportional.

non-linear detection. Square -law detection. Detec-tion in which the operating point is at thepoint of maximum curvature of the tube char-acteristic.

non -linearity. The crowding of television pictureelements in the horizontal direction or crowd-ing of lines at top or bottom due to a distor-tion of the sweep sawtooth.

non-magnetic. Pertaining to materials such asglass, wood, copper, brass, and paper whichare not affected by magnetic fields.

non -resonant line. A transmission line of anylength having terminating devices matchingthe surge impedance so that there are no re-flected (standing) waves. Also a transmissionline having a physical length much shorterthan a quarter wavelength at the operatingfrequency so that the distributed voltage andcurrent are practically uniform.

non -shorting contact switch. A selector switch inwhich the width of the movable contact is lessthan the distance between contacts,

non -storage camera tube. A television camera tubethat produces a picture signal proportionalat any instant to the intensity of the illumina-tion on the corresponding elemental area ofthe scene.

non -synchronous vibrator. A vibrator that only in-terrupts a direct current, without rectifyingthe resulting stepped -up ac pulses.

normal. The perpendicular to the point of con-tact. Also, the expected or regular value.

north pole. The pole of a magnet from which themagnetic lines of force leave.

Novachord. An electronic musical instrument thatcreates the sounds by means of oscillator andamplifier circuits.

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noval socket. A tube socket with openings fornine pins.

nucleonics. The science dealing with phenomenaassociated with the atom nucleus.

nucleus. The central portion of an atom, con-sisting of a proton alone or various combina-tions of electrons and protons. The plural isnuclei.

null. Zero.

null indicator. Any device that will indicate whenthe current is zero.

null method. Any method of measurement inwhich the reading is taken at zero.

number. One or more written or printed charac-ters used to express an amount of units.

numeral. One or more written or printed charac-ters used to express a number. Example:Arabic numerals 1, 2, 3, etc. Roman numeralsI, V, X, etc.

numerator. The part of a common fraction writtenabove the line. Example: In 1/2, the numer-ator is 1.

Oobsolescence -free. Not liable to become out of

date because of new developments or new in-ventions.

obtuse angle. An angle that is greater than aright angle (greater than 90°).

octal base. A tube socket base having eight equal-ly spaced prongs and a central aligning key.

Octal Base

octal socket. A tube socket with openings foreight equally spaced pins, and a slot for acentral aligning key.

octode. A vacuum tube having eight electrodes.oersted. Unit of magnetic intensity or magnetiz-

ing force equal to one gilbert in one centi-meter. Also, formerly the unit of magneticforce of one gilbert divided by a flux of onemaxwell.

ohm. The unit of resistance. The resistance of adevice is one ohm when a de voltage of onevolt will send a current of one amperethrough that device. The Greek letter omega(f/ or a) is commonly used to represent ohm.

ohmic value. The resistance in ohms that a partor circuit offers to the flow of current.

ohmmeter. A test instrument that measures andindicates directly the resistance of a part or theresistance between any two points in a circuit.

Ohm's Law. A fundamental electrical law thatexpresses the relationship between voltage,current, and resistance in a direct current cir-

cult, or the relationship between voltage, cur-rent, and impedance in an ac circuit. Thethree forms of the law in each case are givenbelow, in which E is the pressure in volts,I is the current in amperes, R is the resistancein ohms, and Z is the impedance in ohms.

DC FORMS AC FORMSE=IxR E=IXZI= E R I= E ZR= E= I Z= E= Iohms -per -volt. A sensitivity rating for meters,

obtained by dividing the resistance (of themeter and multiplier resistors) by the full-scale voltage value. The higher the ohms -per -volt rating, the more sensitive is the meter.

omnidirectional. In or from all directions, as theradiation pattern of a vertical antenna.

omnigraph. An instrument for producing MorseCode messages for instruction purposes bymeans of a buzzer and perforated tape.

O network. A network composed of four im-pedance branches connected in series to forma closed circuit similar to a squared letter

opaque. Preventing the passage of light rays.open circuit. A circuit that is not electrically

continuous, that is, one in which current can-not flow.

open -circuit jack. A jack whose circuit contactsare normally open and are closeable onlythrough a properly connected plug.

'open core. In iron core inside a coil withoutan external path, so that the magnetic circuithas a long path through air.

open -wire transmission line. A transmission lineformed by two parallel wires, held apart byspacers.

operating angle. In an amplifier, the portion of acycle during which plate current flows.

operating point. The point on a grid -voltage plate -current characteristic curve of a tube that cor-responds to the de grid bias value and deplate current value for operating conditions.

operating power. The power that is actually sup-plied to the transmitting antenna.

operating voltages. The de voltages applied tothe filament, plate, screen grid, and controlgrid elements of a tube to establish its op-erating characteristics.

operator. A person whose duties include the ad-justment, maintenance, and operation oftransmitting equipment.

opposite side. In a right triangle, the side op-posite an acute angle.

optical pattern. See Christmas tree pattern.optical twinning. A defect occurring in natural

quartz crystals resulting in small regions ofunusable material.

optics. The science that treats of the phenomenaof light.

optimum. Best possible.optimum coupling. That amount of coupling be-

tween two circuits that gives maximum trans-fer of signal energy.

orbital multiplier. A thermionic secondary emis-sion tube in which electrons given off fromthe two sides of a disc cathode are acceleratedand bent into two semi -circular paths thatconverge on a dynode from which the sec-ondary electrons are collected on a plate.

ordinary wave. One of two components into which

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a radio wave is split in the ionosphere by theearth's magnetic field. The 0 wave. See extra-ordinary wave.

ordinate. The coordinate that specifies distancein a vertical direction on an ordinary graph.

orient. To turn or adjust in a definite directionwith respect to some reference.

orthicon. A television pickup tube using a low -velocity scanning beam so that secondaryemission from the caesium -silver globules isreduced.

orthiconoscope. See orthicon.

oscillating current. A current that alternately in-creases and decreases in magnitude and re-verses polarity with respect to time in a defi-nite pattern.

oscillation. The condition of oscillating.oscillator. The stage in a receiver, transmitter,

or other apparatus in which a vacuum tubeand associated parts generate alternating cur-rent energy when fed with direct current en-ergy. Also, a signal generator used by service-men.

oscillator harmonic interference. The result of in-teraction between incoming signals and har-monics of the local oscillator (usually the sec-ond harmonic) in a superheterodyne receiver.

oscillator -mixer -first detector. A single stage thatcombines the functions of the local oscillatorand the mixer -first detector in a superhetero-dyne receiver.

oscillator padder. An adjustable condenser inseries with the oscillator tank circuit of asuperheterodyne receiver, used to make pos-sible better tracking between oscillator andpreselector at the low -frequency end of thetuning dial.

oscillatory circuit. A circuit containing inductanceand capacity having values such that a voltagepulse will produce an oscillatory (alternating)current.

oscillogram. The recorded trace or permanentrecord produced by an oscillograph.

oscillograph. A test instrument that records thewave form of a varying current or voltage.Also, loosely, an oscilloscope.

oscilloscope. A test instrument that shows visual-ly on a screen the wave form of a varyingcurrent or voltage.

osophone. A telephone receiver for use by thedeaf. It applies sound vibrations directly tothe bones of the head.

outlet. A set of terminals to which a device maybe connected. For example, the wall outletfrom which electric power can be obtained.

out of phase. Having wave forms that do not passthrough corresponding values at a particularinstant.

out of sync. Not synchronized Television orfacsimile reception, in which the line or framesweeps or both are not in step with the trans-mitted signals.

output. The useful electrical energy delivered bya signal or power source.

output capacitance. The sum of the direct capac-itances between the output electrode (usuallythe plate) and all other electrodes that con-nect directly or indirectly to the other sideof the circuit.

output impedance. The impedance as measuredbetween the output terminals of an electronic

device, receiver, or amplifier at a definite fre-quency.

output indicator. A meter, tuning eye, or otherdevice used to show changes in output.

output meter. A meter connected to the outputof a receiver or amplifier for the purpose ofmeasuring the output signal strength.

output stage. The final stage in a receiver or afamplifier.

output transformer. An iron -core af transformerused to provide efficient coupling betweenthe output stage of a receiver or af amplifierand its load.

output tube. See power output tube.

overcutting. Defective recording caused by ex-cessive swing of the cutting stylus due to ex-cessive signal level.

overlap. The amount by which the effectiveheight of the scanning spot exceeds the nomi-nal width of the scanning line in a facsimilesystem.

overload. A load greater than that which an elec-trical device is designed to carry.

overload capacity. The current, voltage, or powerlevel beyond which permanent damage occursto an electrical device.

overload relay. A relay that opens a circuit auto-matically when current becomes excessive.

over -modulation. Modulation greater than 100%,resulting in distortion because the carrier iscut off during portions of each modulatingcycle.

overshoot. A peak, spike, or sharp rise beyondthe desired terminating point on a square orpulsed wave.

overtone. A harmonic of a fundamental soundfrequency.

oxide. A combination of an element with oxygen.Rust is an oxide of iron.

oxide -coated cathode. A cathode that has beencoated with oxides of alkaline -earth metals toimprove electron emission at moderate tem-peratures.

oxide -coated filament. A filament coated with ametallic oxide to increase the electron emis-sion.

Ppad. A network of resistors, sometimes variable,

inserted in a circuit to introduce a loss. Usedwhere input and output impedances must bematched or maintained constant.

padder. In a superheterodyne receiver, the trim-mer condenser placed in series with the os-cillator tuning circuit to control the receivercalibration at the low -frequency end of thetuning range.

pairing. Imperfect interlace of lines composingthe two fields of one frame of a television pic-ture. Instead of having the proper equal spac-ing, the lines appear in groups of two.

pan. To move a television camera verticallyand/or horizontally to keep it trained on amoving object or secure a panoramic effect.

panel. A board on which the operating controlsof a radio device are mounted.

panoramic receiver. A radio receiver that permitscontinuous observation on a cathode-ray tube

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screen of the presence and relative strengthof all signals within a wide frequency range.

paper condenser. A fixed condenser consisting offoil plates separated by paraffined or oiledpaper.

parabola. A wave shape in the form of a conicsection resulting from the intersection of acone with a plane parallel to its side. Also aparabolic reflector.

parabolic microphone. A microphone placed at thefocal point of a parabolic sound reflector.

parabolic reflector. A device for collecting light,sound, or radio waves and focusing them to asingle point, or for reflecting them in beamsconsisting of parallel rays.

para-curve cone. A loudspeaker diaphragm hav-ing a paraboloidal shape, used to secure pis-ton action whereby the entire cone moves asa unit. Sometimes called curvilinear cone.

parallel. Connected so that current can flowthrough two or more paths. Also, equally dis-tant and never meeting, as parallel lines. Also,one of the imaginary circles on the surface ofthe earth parallel to the equator, markinglatitude.

parallel cut. A Y cut in a quartz crystal.parallel -plate oscillator. A push-pull ultra -high -

frequency oscillator circuit in which twoparallel metal plates form the tank circuitthat determines the frequency.

parallel resonant circuit. A tuning circuit consist-ing of an inductance and a capacity connectedin parallel with the source.

parallel -rod oscillator. A microwave oscillatorwhose grid and plate tank circuits are formedof parallel rods, wires, or pipes.

parameter. A variable (or changing quantity)that can be used to find other variables.

parasitic element. An antenna director or reflectorthat receives its excitation by induction ordirect radiation from the driven element, andthat reradiates the energy in the proper phaserelationship to get the desired results.

parasitic oscillations. Unintended self-sustainingoscillations or transient pulses in a circuit.

parasitic suppressor. A combination of inductanceand resistance inserted in the grid circuit ofan amplifier to suppress parasitic oscillations.

patchboard. A panel containing a series of singleor double jacks at which various circuits areterminated. The circuits are interconnected byshort cables called patchcords.

> c csa 47Cl Q,OQ

,Q0_10

Courtesy Gates Radio Co.Patch boa rd

patchcord. A short two- or three -conductor cablewith male plugs at each end, used to inter-connect various circuits terminated at a con-trol panel, or patchboard.

peak. The maximum instantaneous value of avarying voltage or current.peak forward anode voltage. The maximum in-

stantaneous plate -cathode voltage in the di-rection in which a vacuum tube is designed topass current.

peaking. Providing more amplification for thehigh frequencies than for the low, used incompensating for loss of high frequencies.

peaking coil. A small coil placed in an amplifyingcircuit to increase response at certain fre-quencies. Specifically, an inductance used ina video amplifier to resonate with the circuitcapacitance beyond the upper limit of theband and thus compensate for high -frequencyloss of gain and to correct the amplifier phaseshift.

peak inverse anode voltage. The maximum in-stantaneous plate -cathode voltage in the di-rection opposite to that in which a tube isdesigned to pass current.

peak load. The maximum current consumed orproduced in a stated period of time.

peak plate current. The maximum instantaneousplate current flowing in a tube.

peak response. Maximum response.peaks. Momentary high volume levels producedduring a program as a natural result ofchanges in pitch, accent, or speech emphasis,

causing the volume indicator to swing upward.Also rises in the response characteristic of anamplifier.

peak -to -peak voltage. The voltage amplitude be-tween the maximum positive and maximumnegative peaks of an ac signal. For a sinewave, this is twice the peak voltage or is 2.82times the rms voltage.

peak voltmeter. A voltmeter that indicates thepeak value of a voltage.

pedestal. The constant voltage value existingjust before and after the synchronizing pulsesoccur in a television signal.

penetration frequency. The highest frequency atwhich a radio wave traveling vertically up-ward will still be reflected regularly by aparticular ionized layer of the ionosphere. Alsocalled the critical frequency.

pentagrid converter. A pentagrid tube used as amixer -detector in a superheterodyne receiver.

pentagrid tube. A tube having five grids.pentatron. A five -electrode vacuum tube contain-

ing two anodes.pentode. A vacuum tube having five electrodes.percentage modulation. In an amplitude -modu-

lated wave, the ratio of half the difference be-tween the maximum and minimum amplitudesof the modulated wave to the average ampli-tude, multiplied by 100 to express it as a per-centage. In a frequency -modulated wave, theratio of the actual frequency deviation to thefrequency deviation required for 100% modu-lation, multiplied by 100 to express it as apercentage.

percentage modulation meter. An instrument usedto measure the percentage of modulation of atransmitter. It may be a meter or a cathode-ray oscilloscope.

percent ripple. The ratio of the rms ripple volt-age value to the average de voltage value atthe output of a rectifier or dc generator, mul-tiplied by 100 to express it as a percentage.

perfect dielectric. A theoretical dielectric ma-terial without losses regardless of frequencyor potential. A perfect vacuum is the onlyknown perfect dielectric.

period. In alternating current, the time requiredfor one cycle or one complete change to takeplace.

periodic. Recurring at equal intervals of time.60

Permalloy. An alloy of nickel and iron used ascore material for high -quality audio -frequencytransformers.

permanent magnet. A piece of hardened steel orother magnetic material that has been arti-ficially magnetized and retains its magnetism.

permanent magnet dynamic loudspeaker. A movingcoil loudspeaker with its field supplied by apermanent magnet.

permatron. A thermionic vacuum tube in whichthe plate current is controlled by a magneticfield instead of a grid.

permeability. A measure of how much better aparticular material is than air as a path formagnetic lines of force. The permeability ofair is assumed as 1.

permeability tuning. A method of varying the in-ductance of an iron -core rf coil by movinga powdered -iron core in or out of the coil.

permeance. The reciprocal of reluctance, mag-netic conductivity.

persistence. The measure of the length of timethe screen of a cathode-ray tube remainsluminescent after the excitation is removed.

persistence of vision. The ability of the eye toretain the impression of an image for a lengthof time after the image has disappeared fromview. The property of the eye that enablesit to fill in the intervals between successiveimages and to produce the illusion of motion.

phanotron. A hot -cathode diode gaesous tube.phantom circuit. A circuit superimposed on two

other circuits. Used in telephone and broad-cast work to make two pairs of wires providethree complete circuits.

phase. An expression of how much of the timeperiod of one cycle of a regularly recurringquantity has been completed, usually measuredfrom a reference time when the quantitypasses through zero from negative to positive.The phase difference of two or more quantitiescan be determined by comparing their phasesat the instant one quantity is at the referencetime. Phase is usually expressed as a phaseangle measured in degrees or radians.

phase angle. A means of expressing the phase ofa regularly recurring quantity in degrees orradians. Phase multiplied by 27r gives thephase angle in radians, and by 360. the phaseangle in degrees. If a cycle has advanced fromzero to maximum, Y4 of the cycle has passed,or the phase is 1/4 and the angle is Y4 X 360 =

7r90°, or 1/4 X 2r = - radians. When two or

2more quantities are being compared, eithertheir phase difference can be converted intoa phase angle, or the difference between theirphase angles can be found, to express theangle of lead or angle of lag between them.

phase deviation. In phase modulation, the amountby which the instantaneous carrier phase dur-ing modulation differs from the unmodulatedphase.

phase difference. The amount by which the phaseof one quantity leads or lags the phase of an-other. It is usually expressed as a phaseangle in degrees or radians.

phase distortion. A condition in which unequalfrequency response causes time delays thatshift the phase of components of a signal.Particularly important in video amplifiers be-cause it changes the peak values of the videosignal and thus alters the contrast and reso-lution.

phase modulation. A system of radio broadcastingin which the amount of deviation in phase of

the carrier signal varies in accordance withthe amplitude of the modulating signal, at arate corresponding to the frequency of themodulating signal.

phaser. In facsimile, a device for adjusting theequipment so that the recorded elemental areabears the same relation to the record sheet asthe corresponding transmitted elemental areabears to the subject copy in the direction ofthe scanning line.

phase reversal. A change in phase of one-halfcycle or 180 degrees.

phase -shift oscillator. An oscillator made by con-necting between the output and the input anynetwork having a phase shift of an odd multi-ple of 180° (per stage) at the frequency ofoscillation.

phase -splitting circuit. A circuit that producesfrom the same input waveform, two outputwaveforms that differ in phase from eachother.

phase velocity. Product of frequency and wave-length.

Phasitron. A tube producing frequency modula-tion. The cathode emits a rotating sheet ofelectrons, the outer edge of which is sinu-soidally modulated. The amount of energyreaching the second anode through holes inthe first anode is determined by the speed ofthe rotating sheet of electrons, which is modu-lated by the intelligence signal.

phasmajector. See monoscope.

phenolic material. An insulating plastic such asBakelite.

phenomenon. Any observable action, change, oroccurrence.

Phillips screw. A screw having an indented crossin its head in place of the conventional slot.

phon. A term sometimes used in place Of decibelto specify equivalent loudness levels.

phone. A headphone.phono adapter. A device connected to an ampli-

fier to provide terminals to which a phono-graph pickup can be connected.

phonograph. See record player. Also a machineusing a spring motor, reproducing recordingsby mechanical means.

phonograph amplifier. An audio -frequency ampli-fier for use with a phonograph pickup.

phonograph connection. Two terminals or a jacksometimes provided on a receiver for makingconnections to a phonograph pickup, permit-ting use of the audio amplifier and loudspeak-er to reproduce phonograph records.

phonograph oscillator. An rf oscillator arrangedfor modulation by the output of a phonographpickup, so that the resulting modulated rf sig-nal can be radiated to the antenna and groundterminals of a radio receiver. This permitsthe playing of records without having to makeany direct connection to the receiver.

phonograph pickup. A device that converts varia-tions in the grooves of a phonograph recordinto corresponding audio signals. It consistsessentially of a needle that converts record -groove variations into mechanical movements,and a crystal, dynamic, or photoelectric cart-ridge that converts these mechanical move-ments into audio signals, mounted in a tonearm.

phosphor. A chemical that has the characteristicof emitting cold light, either fro internalchemical action or from external bxcitation.Specifically, a chemical coating on the face

61

of a cathode-ray tube that becomes luminouswhen bombarded by electrons.

phosphor bronze. A hard, springy alloy of copper,tin, and phosphorous, widely used in radio forcontact springs.

phosphorescence. Light emitted without tangibleheat. Specifically, light given off by a phos-phor after the exciting light of the electronstream has ceased to act. Persistence, after-glow.

photocathode. A cathode that emits electronsunder the influence of light.

photocell. A device for converting variations oflight intensity or color into equivalent elec-trical variations.

photoconductive cell. A light-sensitive cell whoseohmic resistance varies with changes in lightfalling on the cell.

photoelectric. Electrically sensitive to changes inlight.

photoelectric cell. A light-sensitive cell; whichcan be any one of three basic types-photo-emissive, photoconductive, or photovoltaic. Itconverts variations in light into correspondingvariations in voltage or current.

photoelectric emission. Emission of electrons froma body under the influence of light.

photoemissive. Emitting electrons when struckby light.

photoemissive cell. A light-sensitive cell in whicha treated cathode, mounted in a glass enve-lope, emits electrons under the action of light,these electrons being collected by the anode.

photographic recording. Facsimile recording byexposure of a photosensitive surface to a sig-nal -controlled light beam or spot.

photo -ionization. Ionization occurring in a gas asa result of visible light or ultraviolet radia-tion.

photo -island grid. A thin sheet of metal havingmany very fine perforations, used as thephotosensitive surface in the storage -typeFarnsworth television dissector tube.

photometer. An instrument for measuring thebrightness of sources of light.

photometry. A branch of the science of opticsdealing with the measurement of illumination.

photophone. An instrument for transmittingsound over short distances by means of a beamof light.

photosensitive. Responsive to changes in lightintensity.

phototelegraphy. See wire photo.

phototube. A vacuum tube in which the cathodeis radiated with visible or invisible light forelectron -emitting purposes.

photovoltaic cell. A light-sensitive cell that gen-erates a voltage when illuminated, this voltagevarying with the amount of light falling onthe cell. Also called a self -generating cell.

pickup. See phonograph pickup. Also, any devicethat converts original intelligence into anequivalent electrical signal, such as a tele-vision camera or a microphone. Also, the valueof voltage or current at which a relay willoperate.

pictorial wiring diagram. A diagram containingsketches of radio parts and showing the wir-ing between the parts.

picture black. The signal produced at any pointin a facsimile system by the scanning of aselected area of subject copy having maximumdensity.

picture control. See contrast control.

picture element. In a television system, the small-est portion of a picture or scene- that is in-dividually converted into an electrical signal.

picture frequency. See frame frequency.picture jump. Unsteadiness in the vertical direc-

tion of a television picture or of a picture pro-jected by a motion -picture machine.

picture signal. The electrical pulses resultingfrom scanning of successive elements of avisual scene by a scanning device. The videosignal.

Courtesy SylvaniaPicture Tube

picture tube. The image -reproducing cathode-raytube in a television receiver.

picture white. The signal produced at any pointin a facsimile system by the scanning of aselected area of subject copy having minimumdensity.

pie. One layer or section of a multisection wind-ing. Sometimes written pi.

Pierce oscillator. A form of crystal oscillator cir-cuit in which the frequency -controlling crystalelement is connected between grid and plateof the oscillator tube. It needs no tuned platecircuit, and may therefore drive a final ampli-fier or buffer stage with but one tuning con-trol. Used primarily by amateur radio opera-tors.

pie winding. A method of constructing coils froma number of individual washer -shaped coilscalled pies. Also called pi winding.

piezoelectric. Possessing the ability to produce avoltage when mechanical force is applied, orto produce a force when a voltage is applied,especially of a -crystal.

pigtail. A flexible connection between a sta-tionary terminal and a part or terminal thathas limited motion. Also, the connecting leadson parts such as resistors and condensers.

pilot jewel. A clear or colored glass or plasticplaced over or in front of a pilot lamp.

pilot lamp. A small lamp mounted on the panelof a radio receiver to illuminate the tuningdial, or mounted on the panel of other radioapparatus to indicate when the apparatus isturned on.

pi mode. The mode of resonance of a multicavity

62

magnetron for which the phase difference be-tween adjacent anode segments is r radians.

pin connections. Connections made to the pinsof a vacuum tube. The following abbreviationsare used to identify pin connections: NC, noconnection; IS, internal shield; IC, internalconnection (but no electrode connection); P,plate; G, grid; SG, screen grid; K, cathode;H, heater; F, filament; RC, ray -control elec-trode; TA, target.

pine -tree array. Dipole antennas aligned in avertical plane known as the radiating curtainwith a second array containing correspondinghalf -wave antennas parallel to and a quarterwavelength behind, forming a reflecting cur-tain.

pi network. A network of three impendances, twoacross the line and the third inserted in oneline between the two so as to resemble theGreek letter r.

pin jack. A small receptacle into which is pusheda pin -like plug to complete a circuit connectedto the two parts.

pip. A pulse or peak on a wave pattern.piped program. A program that has been trans-

mitted over wires.pipe line. A shielded transmission line consisting

of a wire inside a pipe. Also called coaxial line,coaxial cable, concentric line.

piston action. The movement in or out as a unitof the cone or diaphragm of a loudspeakerwhen driven at bass audio frequencies.

pitch. The frequency of a tone.

plane. A flat surface.plane of polarization. In a radio wave, a plane

perpendicular to the wave front and parallelto the electric component of the wave. In avertically polarized wave, this plane is per-pendicular to the earth. In a horizontallypolarized wave, this plane is parallel to theearth.

plane -polarized wave. A wave in which the direc-tion of the displacement at all points in acertain space is parallel to a fixed plane.

plano-concave. Having one flat and one inwardlycurved surface.

piano -convex. Having one flat and one outwardlycurved surface.

elan -position indicator (PPI). A radar system inwhich a plan or map of an area is shown ona cathode-ray tube.

plate. The principal anode in a tube, usuallyat a high positive potential with respect to thecathode to attract the electrons emitted by thecathode.

plate circuit. A circuit including the plate voltagesource and all other parts connected betweenthe cathode and plate terminals of a tube.

plate current. The current flowing through theplate circuit of a tube and between the plateand cathode inside the tube.

plate detection. Rectification of the radio -fre-quency signals in the plate circuit of a vacuumtube.

plate dissipation. The power in watts expendedas heat in the plates or anodes of tubes. Itis the difference between the plate input powerand the power delivered to the load.

plate efficiency. The ratio of power delivered tothe load (ac) to the plate input power (dc).

plate impedance. See ac plate resistance.

plate input power. The product of the dc voltageapplied to the plates of the tubes in the finalradio stage and the total current flowing tothese plates, measured without modulation.

plate keying. Keying a telegraph transmitterstage by interrupting the plate supply of atransmitter.

plate -load impedance. The total impedance con-nected between anode and cathode.

plate modulation. Modulation produced by intro-duction of the modulating wave into the platecircuit of any tube in which the carrier -fre-quency wave is present.

plate neutralization. A method of neutralizing anamplifier in which a portion of the plate -cathode ac voltage is shifted 180° and appliedto the grid -cathode circuit through a neutral-izing capacitor.

plate resistance. The resistance in ohms of theplate -cathode path in a tube. See de plateresistance and ac plate resistance.

plate saturation. The condition in which furtherincrease of the plate voltage will not resultin an increase of the plate current becauseall of the electrons being emitted by the cath-ode are being collected by the plate. Alsoknown as voltage saturation.

plate supply. The voltage source used in a tubecircuit to place the plate at a high positivepotential with respect to the cathode.

plate -to -plate -impedance. The load impedancemeasured between the plates of a push-pullamplifier stage.

plate voltage. The de voltage existing betweenthe plate and cathode terminals of a tube.

pliotron. A high -vacuum thermionic tube havingone or more grid electrodes to control themagnitude of the unidirectional current flow.

plug. A device inserted in a terminal jack or out-let, used for conveniently making or breakingconnections.

plug-in coil. A coil having as its terminals anumber of prongs arranged to fit into a socketmounted on the radio chassis.

plug-in resistor. A filament voltage -droppingresistor mounted in a metal or glass enclosureand provided with a plug-in base.

plumbing. Popular term for microwave wave -guides and associated equipment.

plus sign. A sign (±) used in mathematics toindicate addition or a positive value. Used inradio to indicate the positive terminal of avoltage source or positive polarity.

PM dynamic loudspeaker. See permanent magnetdynamic loudspeaker.

pneumatic loudspeaker. A loudspeaker in whichthe output is created by controlled variationof an air stream. Also, a loudspeaker encasedin a hornlike baffle into which air is pumpedunder pressure to raise its efficiency.

pointer. The part of a meter or tuning dial thatmoves over the scale; an indicator.

point-to-point communication. Radio communica-tion between two definite fixed stations.

point-to-point resistance. A method of testingwherein the resistance between given pointsin a set is measured and checked against ex-pected normal values.

poison. In television or electronics, a substancethat reduces phosphorescence in a luminescentmaterial. Also, a contaminant that reducesemission.

63

proton. The natural, elemental quantity ofpositive electricity. The mass of the protonis 1849 times that of the electron. A protonhas the same quantity of positive electricityas an electron has of negative electricity.hence one proton balances one electron.

protractor. An instrument for measuring or con-structing angles.

public address amplifier. An audio amplifier capa-ble of supplying sufficient audio power toloudspeakers for adequate sound coverage ofpublic gatherings.

public address system. A complete system for re-producing voice and speech with adequatevolume for large public gatherings. It in-cludes one or more microphones, a powerfulaudio amplifier with suitable power supply,and a sufficient number of loudspeakers togive coverage of the audience area.

pulling. Forcing the frequency of an oscillatorto change toward another frequency by someform of coupling or loading.

pull-up current. The minimum current that willcause the armature of a relay to be pulled upagainst the relay core.

pulsating current. A current that changes invalue but not in direction.

pulse. A momentary sharp change in a currentor voltage.

pulse -amplitude modulation (PAM). Amplitudemodulation of a pulse carrier.

pulse cross. When driving or synchronizing pulsesare displaced from their usual positions andare fed to the picture tube, a cross appearson the raster showing graphically the rela-tions between the pulses.

pulse -decay time. The time required for the in-stantaneous amplitude to go from 90% to 10%of the peak value.

pulsed oscillator. An oscillator that is made tooperate during recurrent intervals by self -generated or externally applied pulses.

pulse duration. The elapsed time between thestart and finish of a single pulse.

pulse -duration modulation (PDM). A form of pulse -time modulation in which the duration of thepulse is the characteristic varied.

pulse -frequency modulation (PFM). A system inwhich the number of pulses in a given time isvaried according to the modulation.

pulse generator. A device that generates pulses.Specifically, one for generating pulses forsynchronizing purposes in a television system.

pulse -interval modulation (PIM). A form of pulse -time modulation in which the pulse intervalis the characteristic varied.

pulse -length modulation (PLM). See pulse -durationmodulation.

pulse modulation. The modulation of a carrierconsisting of a series of pulses, by changingeither the amplitude, frequency, or a timecharacteristic of the pulses.

pulse modulator. A device that applies pulses tothe element in which modulation takes place.

pulse operation. Method of operation in whichthe energy is delivered in pulses.

pulse -position modulation (PPM). A form of pulse -time modulation in which the position intime of a pulse is the characteristic varied.

pulser. Electronic equipment for the production

of high voltage pulses of extremely shortduration occurring at definite recurrencerates.

pulse repeater. A device used for receivingpulses from one circuit and transmitting cor-responding pulses into another circuit.

pulse repetition rate. The number of pulses oc-curring in a given unit of time.

pulse -rise time. The time required for the in-stantaneous amplitude to go from 10% to90% of the peak value.

pulse separator. A television receiver circuit thatseparates the horizontal and vertical pulses.

pulse -time modulation (PTM). Modulation in whichthe time of occurrence of some characteristicof a pulse carrier is varied, such as the pulseduration, the pulse position, or the intervalbetween pulses.

pulse width. See pulse duration.

pulse -width modulation (PWM). See pulse -durationmodulation.

pure tone. A sound produced by sinusoidal soundwaves of a single frequency.

push -back hookup wire. Tinned copper hookupwire covered with a loosely braided cottoninsulation that can be pushed back from theend of a wire length to expose sufficient barewire for a connection.

push-button switch. A device that opens or closesa circuit by means of pressure upon a button.

push-button tuner. A tuning unit that automati-cally tunes a receiver to a station when thebutton assigned to that station is pressed.

push-pull circuit. A two -tube circuit so arrangedthat both tubes operate simultaneously andtheir individual plate currents add in thecommon load to balance out all even har-monics that would otherwise cause distortion.

push-pull oscillator. A balanced oscillator withtwo similar tubes in phase opposition.

push-pull transformer. An iron -core of transform-er designed for use in a push-pull amplifiercircuit.

push -push circuit. A two -tube circuit so arrangedthat the tubes operate alternately into acommon load.

pyrometer. An instrument for measuring hightemperatures.

QQ. The merit (degree of perfection) of a coil

or condenser, equal to its reactance dividedby its resistance.

Q factor. See Q.

9 signal. One of the three -letter abbreviationsstarting with Q in the International List ofAbbreviations, used to represent complete sen-tences in radiotelegraphy. When the questionform of the sentence is intended, the codesignal for an interrogation mark is sent afterthe abbreviation. Thus, QRM means "I ambeing interfered with," and QRM? means"Are you being interfered with?" Other com-mon Q signals used in a similar manner are:QRN, Atmospheric interference. QRT, Stopsending, used to clear bands in emergency.QRX, Wait. QSY, Shift frequency.

QSL card. A card sent by a radio amateur toverify communication with another amateur.

66

quadrantal error. Error in direction finder read-ings caused by re -radiated energy from metalsurfaces of an airplane that is 90° out of phasewith the original signal.

quadratic equation. An equation containing thesquare of the unknown quantity and no higherpower. Examples: P = I°R; 9x, + 7x = 60.

quadrature. Displaced 90° in phase angle.

quantitative. Capable of measurement.

quarter -wave antenna. An antenna electricallyequal to one-fourth the wavelength of the sig-nal transmitted or received.

quarter -wave transformer. A section of transmis-sion line one -quarter wavelength long, usedas an impedance -matching transformer.

quarter -wave transmission line. A transmission linethat is an electrical quarter -wavelength of thefrequency for which it is designed.

quartz. A natural crystalline material widelyused as the source of piezoelectric crystals.

Courtesy Bell '1'elenhoia

Quartz Crystal

Laboratories

quartz crystal. A thin slab cut from a naturalcrystal of quartz and ground to a thicknessthat will make it vibrate at the desired fre-quency when supplied with energy. It is usedas the master carrier frequency source in thecrystal oscillator stage of a transmitter.

quartz oscillator. See crystal oscillator.quasi -optical. Having properties similar to light

waves in their propagation; said of micro-waves.

quasi -single sideband. See vestigial sideband.quenching frequency. A locally generated fre-

quency produced in a super -regenerative de-tector stage at regular intervals to preventoscillation during reception.

quenching signal. See quenching frequency.

quick -break fuse. A fuse that opens a circuitrapidly when it is overloaded, to preventarcing.

quiescent carrier telephony. A radiotelephony sys-tem in which the carrier is suppressed when-ever there are no voice signals to be trans-mitted.

quiescent operating point. The value of voltage orcurrent characteristic of a vacuum tube cir-cuit when no signal is being transmitted orreceived.

quiet automatic volume control. A noise limiter cir-cuit that blocks an i-f or of stage until a cer-tain signal strength is reached, and whichdoes not therefore apply full amplification tobackground noise when tuning between sta-tions.

quiet tuning. A means of silencing the output of areceiver at all times except when it is accurate-ly tuned to an incoming carrier wave.

quieting sensitivity. The minimum signal inputrequired to give a prescribed output signal-to-noise ratio.

quotient. The result obtained by division. Ex-ample: in 1400 -+- 70 = 20, the quotient is 20.(The dividend is 1400, and the divisor is 70.)

Rracon. Radar beacon used as a navigational aid.

radar. (Coined from the phrase, RAdio Detec-tion And Ranging.) A system for determin-ing the presence and location of a distant ob-ject by transmitting high -power microwavepulses that are reflected back by the object.This reflected energy appears as a "pip' onthe screen of a cathode-ray tube; the positionof this pip on a calibrated axis indicates thedistance of the target.

radar trace. The pattern produced on thecathode-ray screen of a radar unit.

radar transmitter. The transmitter of a radiodetecting and ranging system.

radial lead. A lead coming from the side of acomponent, rather than axially from the end.

radian. An angle which, when placed with itsvertex at the center of a circle, intercepts anarc equal in length to the radius of the circle.A complete circle contains 2ir radians, hence1 radian is 57.2959°, and 1° is 0.01745 radian.

radiant energy: Energy in the form of electro-magnetic radiation such as radio waves, heatwaves, or light waves.

radiate. To emit electromagnetic or heat wavesinto space.

radiating curtain. An antenna array of dipolesplaced in a vertical plane to reinforce eachother.

radiating guide. An ultra- to super -high -frequencywavegu.ide designed to radiate energy intofree space.

radiation. The process of emitting waves, as ofradio waves from an antenna.

radiation efficiency. A transmitting antenna rat-ing, equal to the ratio of the power radiatedto the total power supplied to the antenna ata given frequency.

radiation field. Space containing electromagneticlines of force.

radiation pattern. A diagram showing how wealan antenna system radiates or picks up radiowaves in all directions in one plane.

radiation resistance. That part of the total re-sistance of an antenna that causes energy tobe radiated into space instead of being dissi-tpoa

tehdear aheat ed

sp aw erh e( aenenmnian. eIdt throughl

field strength measurements) divided by thesquare of the antenna current at a point ofmaximum current.

radical sign. The sign V, placed before a num-ber to indicate that its square root is to beextracted. When some other root is to be ex-tracted, the index number of that root isplaced in the angle of the radical sign. Exam-ples: 1/49 means square root of 49, which is7; NY64 means cube root of 64, which is 4.

radicand. The number or quantity after a radicalsign. Example: In fix, the radicand is x.

radio. The art of communication by means ofradio waves traveling through free space, as

67

In sound, television, facsimile, etc., as dis-tinguished from wired radio, in which rf cur-rents are transmitted over wire lines. 'Also, areceiving set capable of picking up radio wavesand reproducing the intelligence they convey.

radioactivity. The emission of radiant energy byan element or material, either spontaneouslyor under the influence of an activating device.

radio altimeter. A device for determining thealtitude of an airplane, consisting of a trans-mitter sending pulses which are reflected fromthe earth to a receiver. The time between thesending and receiving of a pulse indicates thealtitude.

Radio and Television Manufacturers Association(RTMA). Formerly Radio Manufacturers As-sociation (RMA). An organization of leadingmanufacturers of radio and television equip-ment, active in proposing standards of sizesand designs of parts and standardizing termsand definitions.

radio beacon. A radio transmitting station thatis fixed in location and transmits a character-istic signal that can be used by mobile (shipor aircraft) stations to determine bearings,locations, or courses.

radio bearing. The angle between the directionof travel of a radio wave and due north.

radio communication. The radio transmission andreception of any form of intelligence, such aswriting, signs, signals, pictures, and soundsof all kinds.

radio compass. A radio direction finder used chief-ly in marine and aircraft radio stations fornavigational purposes.

radio control. The control of moving objects suchas airplanes, automobiles, ships, and torpe-does, by means of signals transmitted overradio waves from the transmitter location tospecial radio receiving equipment in the ob-ject being controlled. Also called remote con-trol.

radio direction finder. A radio receiving devicethat can be used to determine the line oftravel of radio waves.

radio direction finding (rdf). Determining directionby means of radio. Also British term for radar.

radio fadeout. Partial or complete blocking ofradio waves by a sudden ionospheric disturb-ance.

radio field intensify. See field intensity.radio frequency. A frequency at which It is pos-

sible to get useful electromagnetic radiationfor communication purposes.

radio -frequency amplifier. A vacuum tube ampli-fier stage to provide amplification at radiofrequencies.

radio -frequency choke. A choke coil designed tohave high impedance at radio frequencies.

radio -frequency transformer. An air -core or pow-dered -iron core transformer used in rf cir-cuits.

radio landing beam. A radio beam that serves forvertical guidance of aircraft when landingduring unfavorable weather conditions.

radio link. The carrying of a program (sound ortelevision) from point of pickup to main studioby means of radio instead of telephone lines.

Radio Manufacturers Association (RMA). See Radioand Television Manufacturers Association.

radio marker beacon. A radio beacon station usedfor marking the location of a point, a boun-

dary, or a small area, such as for aircraftblind -landing systems.

radio metal locator. A radio instrument that in-dicates the presence of metal nearby by achange in meter reading or a change in a tonesignal heard in headphones.

radio meteorograph. A combination meteorographand radio transmitter carried aloft by an un-manned balloon and so designed that it willtransmit back to earth ultra -high -frequencysignals that can be interpreted by ground ob-servers in terms of the pressure, temperature,and humidity at regular intervals during theascent of the balloon into the stratosphere.When the balloon bursts, the instrument islowered to earth by a parachute. Also calledradiosonde.

radio navigation. Use of radio signals for course -plotting.

radio photogram. A photograph transmitted byradio.

radio prospecting. Use of radio equipment tolocate mineral or oil deposits.

radio proximity fuze. A radio device contained ina missile to detonate it within predeterminedlimits of distance from a target by means ofelectromagnetic interaction with the target.

radio range station. A radio beacon station thattransmits waves in definite directions, in sucha way that departures from a given course canbe observed by aircraft or ships.

radio receiver. An instrument that amplifiesradio -frequency signals, separates the rf car-rier from the intelligence signal, amplifiesthe intelligence signal additionally in mostcases, then converts the intelligence signalInto sound waves.

radiosonde. See radio meteorograph.radio spectrum. All the wavelengths or frequen-

cies that can be used for the transmission ofenergy, communications, or signals by radio.These frequencies are classified into bandswith designations and abbreviations as givenin the table on the next page.

radio station. A station equipped to engage inradio communications or radio transmission ofenergy. A station includes all apparatus usedat a particular location for one class of serv-ice. Radio stations are classified according tothe nature of the service they furnish.

radio station interference. Interference caused byradio waves from one or more undesired sta-tions.

radio telegraphy. Radio communication by meansof the International Morse Code.

radiotelephone transmitter. A transmitter capableof sending voice and music, as contrasted witha radiotelegraph transmitter, which can sendonly code.

radio telephony. The transmission of voice ormusic through space by means of modulatedrf waves.

radio transmitter. A device for producing rf powerfor radio transmission.

Radlotrician. A graduate of the National RadioInstitute, thoroughly trained as a radio serv-iceman or radio operator.

radio wave. A combination of electric and mag-netic fields varying at a radio frequency, andcapable of traveling through space.

radio -wave propagation. The transfer of energyby electromagnetic radiation.

68

radius. The distance from the center of a circleor arc to any point on that circle or arc.

radome. A streamlined antenna housing used onairplanes.

random winding. A winding made with no regardfor the position of the turns or layers in refer-ence to each other.

range. Extent of coverage or effectiveness, ormeasure of distance.

raster. The illuminated rectangular area scannedby the electron beam in a picture tube, visi-ble when the brilliancy control is turned upwith no signal.

rated output. The power, voltage, or current adevice will provide when operated under spe-cified conditions.

ratio. The value obtained by dividing one num-ber by another.

ratio detector. An FM detector that uses a pairof diodes connected in such a manner that theaudio output is propotional to the ratio ofthe FM voltages applied to the two diodes.

ray. The path along which electrons or lightwaves travel in space.

RC circuit. A time -determining network of re-sistors and capacitors in which the time con-stant is defined as the product of the resistanceand the capacitance.

R -C coupling. Resistor -capacitor coupling betweentwo circuits.

R -C oscillator. Any oscillator in which the fre-quency is determined by resistance -capacitanceelements.

reactance. That part of the impedance offered tothe flow of alternating current by the induct-ance or capacity of a part or circuit. React-ance is measured in ohms, and depends uponthe frequency of the alternating current aswell as upon the value of inductance or capac-ity.

reactance modulator. A stage used in frequency -modulation transmitters in which a vacuumtube acts as a reactance that varies in ac-cordance with the intelligence modulation,causing the frequency of the oscillator stageto vary accordingly.

reactance tube. A tube that draws plate currentout of phase with the plate voltage because ofthe circuit arrangement, and therefore resem-bles a reactance.

reactive. Pertaining to inductive or capacitivereactance.

reaetor. A device that introduces reactance,either inductive or capacitive, into a circuit.A coil or condenser.

receiver. A device for receiving radio waves.

receiving antenna. A conductor or system of con-ductors used for the reception of radio signals.

receptacle. A socket or outlet into which a plugcan be pushed or screwed for the purpose ofmaking an electrical connection.

reciprocal. The reciprocal of a number is 1 di-vided by that number. Example: IA is thereciprocal of R.

recorder. An instrument that makes a record ofa signal.

recording. A phonograph record. Also, the processof making records or of registering the re-ceived signal upon the record sheet of a fac-simile receiver or measuring instrument.

recording disc. An unrecorded or blank disc usedfor sound recording purposes. Also called arecording blank.

recording head. The device that cuts a grooveon a disc, or magnetizes a steel wire or mag-netic tape in accordance with the sound beingrecorded.

recording level. The db or vu output of an audioamplifier used for recording.

record player. A motor -driven turntable and anelectric pickup used for converting the vari-ations on a phonograph record into electricalsignals.

rectangular coordinates. The two values thatspecify the position of a point on a graph withrespect to two reference linesto each other.

rectification. The process of changing alternatingcurrent into a current that flows in only onedirection, usually a pulsating direct current.

rectifier. A device that changes an alternatingcurrent into a pulsating direct current.

rectilinear scanning. The process of scanning anarea in a predetermined sequence of narrowstraight parallel strips.

re-entrant cavity. A resonant cavity with one ormore sections directed inwards, so the electricfield is confined to a small area or volume.

reference level. The starting or zero point fromwhich a scale is laid out or from which meas-urements are made.

FREQUENCY CLASSIFICATION IN THE RADIO SPECTRUM

Frequencies Designations Abbreviations

AboveCC

gi

10 ke to30 kc to

300 kc to3 mc to

30 mc to300 mc to

3000 me to

30 kc inclusive300 kc

3 me30 mc

300 me3000 mc

30,000 me

it

it

CC

Cl

CC

Very LowLowMediumHighVery HighUltra HighSuper High

VLFLFMFHFVHFUHFSHF

69

reference recording. Recording of a radio pro-gram or other material, made for the purposeof checking.

reflected impedance. The effective impedance thatappears across the primary of a transformerwhen a load is connected to the secondary.

reflected resistance. The effective resistance thatappears across the primary of a transformerwhen a load is connected across the secondary.

reflected wave. The wave caused by the reflectionof part of an incident or oncoming wave.

reflecting curtain. A vertical array of half -wavereflecting antenna elements, generally usedbehind a radiating curtain of a number of di-poles, to form a high -gain antenna array.

reflection. A change in the direction of wavesafter impinging on a surface.

reflection altimeter. An aircraft altimeter depend-ing on the reflection of radio waves from theearth for the determination of altitude. Seeradio altimeter.

reflection, law of. The angle of reflection is equalto the angle of incidence, both measured fromthe normal to the surface.

reflection loss. The power lost in a transformeror transmission line because of a difference inthe impedances of the source and load.

reflector. In a directional antenna system, aparasitic element in back of the antenna, thatIncreases radiation or reception along a linepointing away from it toward the antenna.Also, an electrode, sometimes called a repeller,whose primary function is to reverse the di-rection of an electron stream.

Courtesy The American Phenolic Corp.

Antenna with Reflector

reflector voltage. The voltage between the re-flector electrode and the cathode in a reflexklystron.

reflex circuit. A circuit through which a radiosignal passes both before and after a changein its frequency.

reflex klystron. A klystron tube in which one setof grids is made to act both as the buncher andthe catcher through the use of a reflector orrepeller plate.

refracted wave. The wave caused by the refrac-tion (change in direction) of the part of anIncident or oncoming wave that travels into adifferent mediurh.

refraction. The bending of a light, heat, sound,or radio wave passing obliquely from onemedium into another, in which the velocity ofpropagation is different from that in the *firstmedium.

regeneration. A method of securing increased out-put from an amplifier by feeding a part of theamplifier output back to the amplifier in sucha way that the signal is in phase with theinput. Also called positive feedback.

regenerative detector. A vacuum tube detector inwhich intentional feedback of rf energy fromthe plate circuit to the control grid circuit

produces regeneration, greatly increasing theuseful amplification.

regenerative receiver. A radio receiver that usescontrolled regeneration to increase the ampli-fication provided by a vacuum tube stage.

registry. The superposition of one image on an-other, as in the formation of an interlacedscanning raster.

regulated power supply. A power supply designedto have a constant voltage or current outputunder conditions of varying load or inputpower.

regulation. Ability to maintain constant outputdespite variations in load.

regulator. A device that accomplishes regulationwithin desired limits.

Relnartx crystal oscillator. A crystal -controlledvacuum -tube oscillator featuring a resonantcircuit connected between cathode and ground,tuned to half the crystal frequency.

reinserter. A circuit for establishing the dc levelof a wave form. See clamping.

reinsertion of carrier. The combining of an in-coming suppressed -carrier signal with a local-ly generated carrier signal in the receiver.

relaxation oscillator. An oscillator circuit in whichalternate charging and discharging of a con-denser through a resistance determines thenumber of pulses, so the frequency is deter-mined by the time constant of the condenserand resistor.

relay. An electromagnetic switch that permitscontrol of current in one circuit by a muchsmaller current flowing in another circuit.

relay transmitter. A transmitter that rebroadcaststelevision or sound programs to increase theservice area. Often called repeater station.

reluctance. Opposition offered to magnetic flux.reiuctivity. The reciprocal of permeability.remanence. The magnetic flux density remaining

in a magnetic circuit after the removal of anapplied magnetomotive force.

remote control. Control of any device from a dis-tance.

remote cut-off tube. A variable -mu tube in whichthe spacing of the control grid wires is widerat the center than at the ends. The amplifica-tion of the tube does not vary In direct pro-portion to the bias, and some plate currentflows even at high values of negative bias onthe grid.

remote pickup. Any program not originating Inthe studio.

repeater. An amplifying station used to boostthe volume on long telephone lines.

repeat point. A second position of a superhetero-dyne tuning dial at which reception of a givenstation recurs.

reproducer. A device for converting an electricalsignal into some form capable of being per-ceived by the senses. Specifically, a loud-speaker, picture tube, or facsimile reproducer.

reproduction speed. The area of copy recordedper unit time in a facsimile system.

re -radiation. Return of energy to space by a de-vice such as a receiving antenna that has ex-tracted energy from space.

re-recording. A recording made from the play-back of a recording.

70

residual charge. The charge remaining on theplates of a capacitor after discharge.

residual gases. The small amount of gas remain-ing in a tube after evacuation.

residual magnetic induction. Residual magnetism.residual magnetism. Magnetism that remains in

the core of an electromagnet atter the elec-trical circuit has been broken.

resistance. The opposition a device or materialoffers to the now of current, as a result ofwhich electric energy is converted into heator radiant energy. Resistance is the only op-position to dc. In an ac circuit, the total op-position is known as the impedance; wherethere is negligible reactance, the impedanceequals the resistance, but where there is ap-preciable reactance, the impedance is a com-bination of the two. Because of skin effect,losses in iron cores, etc.. the resistance in acircuit may be somewhat higher for ac thanfor dc, and is called ac resistance to distinguishit from the lower dc resistance of that samecircuit.

resistance box. See decade box.

resistance bridge. See Wheatstone bridge.resistance -capacitance coupling. The coupling to-

gether of two vacuum tube stages or circuitsby means of resistors and condensers.

resistance coupling. Another name for resistance -capacitance coupling.

resistance drop. The voltage drop occurringacross a resistance when a current flowsthrough it. An IR drop.

resistance loss. See 12R loss.resistance pad. A system of resistors used to re-

duce signal strength, change impedance, orisolate one circuit from another.

resistance wire. Wire made from an alloy havinghigh resistivity.

resistivity. The resistance of a unit cube of amaterial.

resistor. A radio part that offers resistance to theflow of electric current.

resistor core. The support on which a resistorelement is wound.

resistor element. The part of a resistor that pos-sesses the resistance property.

resolution. Degree of reproduction of the detailof a televised scene. The definition.

resolution chart. A television test pattern con-taining a number of converging lines. Thepoint on the screen where these lines seem tomerge into one, determines the maximumresolution of the image.

resolution pattern. See resolution chart.resolution wedge. On a television test pattern, a

group of gradually converging lines used tomeasure resolution.

resonance. In a circuit containing both induc-ance and capacity, a condition in which theinductive reactance is equal to and cancelsout the capacitive reactance.

resonance bridge. See impedance bridge.resonance curve. A frequency response curve that

shows in graphical form the manner in whichany apparatus containing a resonant circuithandles or amplifies the various frequenciesat or near the resonant frequency.

resonance indicator. A device, such as a meter or

neon lamp, that provides visual means ofshowing resonance in a circuit.

resonant circuit. A circuit containing inductanceand capacity. Specifically, a circuit in whichthe inductance and capacity values have beenchosen so the circuit will resonate at a desiredoperating frequency.

resonant current step-up. The increase of the cur-rent in a parallel resonant circuit at resonance,over the line current fed into it.

resonant frequency. The frequency at which theinductive and capacitive reactances are bal-anced.

resonant line. A transmission line whose lengthmakes it resonant at the transmitted fre-quency, or one tuned to such a frequency byadding the proper inductance or capacity to it.

resonant -line oscillator. A self-excited ultra -highfrequency oscillator using parallel rods toform the grid and plate inductances.

resonant resistance. The resistance offered by aparallel resonant circuit at resonance.

resonant voltage step-up. The increase in voltageacross each element of a series resonant cir-cuit at resonance, over the source voltage.

resonate. To bring to resonance, as by tuning.resonator. A hollow chamber forming the tuned

circuit of a microwave oscillator. See cavityresonator.

response. The amplification of a device at a par-ticular frequency.

response characteristic. A curve showing theresponse of a radio device, circuit, or systemover a range of frequencies.

resting frequency. The assigned carrier frequencyof a radio station using the frequency modu-lation system of broadcasting. The restingfrequency is radiated only during intervalswhen no sound waves are being transmitted.

retarding -field oscillator. An oscillator using avacuum tube in which the electrons oscillateback and forth through a grid maintainedpositive with respect to the cathode and theplate. The field in the region of the grid exertsa retarding effect that draws electrons backafter passing through it in either direction.

retentivity. The property of retaining magnetismafter the magnetizing force has been removed.

retentivity of vision. See persistence of vision.retrace. The path traveled by an electron beam

from the end of one line or field to the startof the next line or field. Flyback.

retrace lines. Lines on a cathode-ray tube madeduring the retrace.

retrace time. The time required for the spot toreturn after each sweep. It is also referredto as return time or flyback time.

return wire. The ground or common lead.reverberation. The continuation of sound by ex-

cessive reflection.reverberation time. The time in seconds required

for a sound of a given frequency to decrease,after the sound source is stopped, to one mil-lionth of its initial value.

rf power supply. A high -voltage "power supplysometimes used in television receivers, con-sisting of an rf oscillator whose output is fedthrough a step-up transformer to a rectifier.

rheostat. A variable resistor having a movablecontact controlled by a knob, so that the71

amount of resistance in use can be easily ad-justed while the circuit is electrically alive.

rhombic antenna. A directional antenna consistingof tour long wires arranged to form a rhombus(a parallelogram with all four sides equal,like a diamond).

Rhumbatron. See cavity resonator.ribbon microphone. A moving -conductor micro-

phone in which the moving conductor is asingle corrugated metal ribbon mounted be-tween the poles of permanent magnets. Oftencalled a velocity microphone.

ride gain. To control the volume range of a pro-gram electrically in order to transmit it overlines and equipment at a level above the noiselevel but below the overload level.

Rieke diagram. A graph used to determine thefrequency of operation and power output of amagnetron from the standing wave ratio andthe phase of the reflected signal.

rig. A complete system of components. Thus, anamateur rig is the complete amateur stationconsisting of receiver, transmitter, and all ofthe accessories used with this equipment.

right angle. The angle formed by two straightlines which meet at an angle of 90°.

right-handed elliptically polarized wave. An ellip-tically polarized wave in which the rotationof the direction of displacement is clockwisefor an observer looking in the direction thewave is traveling.

right-hand taper. A concentration of the resistancetoward the counter -clockwise end of a po-tentiometer or a rheostat when held with theshaft pointing toward the observer.

right triangle. A triangle in which one of theangles is a right angle (90').

rim -drive. A method of driving a phonograph orsound recorder turntable with a rubber -cov-ered wheel in contact with the rim of theturntable.

ringing. An oscillation occurring as a result of asudden change in input signal.

ring oscillator. An arrangement of two or morepairs of tubes operating as push-pull oscilla-tors around a ring, usually with alternatesuccessive pairs of grids and plates connectedto tank circuits. Adjacent tubes around thering operate in phase opposition.

ripple. An alternating -current component presentin the output of a dc voltage supply.

ripple current. The alternating -current componentof a pulsating unidirectional current.

ripple factor. The effective value of the alter-nating components of voltage or current di-vided by the direct or average values of thevoltage or current.

ripple filter. A filter that passes only frequenciesbelow a critical cut-off frequency, used toreduce the ripple current of a rectifier or degenerator while allowing direct current to passfreely.

ripple frequency. The frequency of the ripplecurrent.

ripple voltage. The alternating component of theunidirectional voltage from a rectifier or gen-erator used as a source of direct -current power.

rise time. See pulse rise time.RMA color code. A standard method of designat-

ing part values and part leads by coloredmarkings, developed by the Radio Manufac-turers Association.

rms. Root mean square, the effective value of analternating current. It corresponds to the di-rect current value that will produce the sameheating effect.

Rochelle salt crystal. A crystal of sodium potas-sium tartrate, having a pronounced piezoelec-tric effect, used in crystal microphones andcrystal phonograph pickups.

rocking. A term applied to the back and forthrotation of the main tuning gang as the os-cillator padder in a superheterodyne receiveris adjusted at the low -frequency end of thedial.

Roentgen ray. The x-ray.Roentgen. Wilhelm Konrad. German physicist

(1845-1923), the discoverer of the X-ray.root. A number which, when multiplied by itself

a number of times, equals a given number. Theradical sign V is used to indicate square root,and the radical sign with an index numberin its angle is used to indicate any other root.Example : NY312 = 5, which means that thefifth root of 3125 is 5.

root mean square (rms). The square root of theaverage of squares of values uniformly dis-tributed throughout a cycle.

rosin -core solder. Solder that has as its core thecorrect amount of rosin flux for effective radiosoldering work. The rosin is released auto-matically as the solder is applied to the heatedjoint.

rotary beam antenna. A highly directional short-wave receiving or transmitting antenna systemmounted in such a way that it can be rotatedto any desired position either manually or byan electric motor drive.

rotary converter. A dynamo having a single arma-ture equipped with both slip rings and a com-mutator, so that both ac and dc can be ob-tained from it simultaneously if used in con-junction with a motor or engine.

rotary spark gap. A type of spark gap using arotating disc having studs from which sparksleap to one or more stationary electrodes whenhigh voltage is connected between disc andstationary electrodes.

Rotary Switch

rotary switch. Any switch thatrotating a control knob.

rotor. A rotating part, such as the rotating arma-ture of an electric motor or generator.

rotor plates. The movable plates of a variablecondenser.

Ruhmkorff coil. See induction coil.

is operated by

rumble. Low -frequency vibration mechanically72

transmitted to the recording or reproducingturntable and superimposed on the reproduc-tion.

Ssafety factor. The ratio of the normal operating

rating, to the maximum safe rating.sal ammoniac. Ammonium chloride. A chemical

used in primary cells.sampler. A switching arrangement used to con-

nect circuits in rapid succession. In color tele-vision, the sampler of the transmitter switchesin signals for each of three colors in a specifiedorder. At the receiver, the sampler routes thethree color signals in proper order to the re-producer.

sampling. The process of switching to get smallsegments of each cycle at a time.

sapphire. A gem used in the tips of high-gradephonograph needles and in cutting needlesused with sound recorders.

saturation. In a magnetic circuit, the conditionwherein increases in magnetomotive force pro-duce negligible additional flux. Also see platesaturation and temperature saturation.

sawtooth. A voltage or current wave form thatrises linearly to its peak and then drops rapid-ly back to its starting level.

sawtooth generator. A neon or thyratron relaxa-tion oscillator or a vacuum -tube oscillator pro-viding an alternating voltage characterizedby a sawtooth wave form.

scalar quantity. A quantity that has only magni-tude, and no direction.

scale. A series of marks printed on a surfaceover which an indicator moves, or which movespast an indicator.

scale division. A region between one line and thenext adjacent line on a scale.

scaling circuit. A circuit that actuates a countingdevice on receiving a predetermined number ofpulses.

scanner. The part of a facsimile transmitter thatsystematically translates the densities of theelemental areas of the subject copy into signal -wave form.

scanning. The process of successively convertingthe amount of light present in each of thepicture elements that make up the total areaof a picture or scene into electrical signals fortelevision or facsimile transmission. Also, thereverse process at the receiver.

scanning disc. A rotating disc having a spiral rowof holes or lenses near the edge, used in somemechanical television systems to break up apicture or scene into elemental areas, or toreconstruct televised scenes.

scanning line. A single continuous narrow strip,produced by the process of scanning in tele-vision or facsimile.

scanning linearity. In television, the uniformityof scanning speed during the trace interval.

scanning spot. The area viewed at any instant bythe scanner in a facsimile system. Also, thecross-sectional area of the electron beam ateither the camera or picture tube in a TVsystem.

scanning yoke. The electromagnetic coils that pro-vide controlled deflection of the electron beamin a cathode-ray tube.

scattered reflections. Reflections from a regionof the ionosphere, which interfere and causerapid fading. They are variable in respect totime of occurrence, geographical distribution,intensity, and frequency range.

schematic diagram. A diagram that shows elec-trical connections of an electronic device bymeans of symbols used to represent the parts.

Schmidt system. An optical system used to pro-duce large projection images. A large hemi-spherical mirror is used to project the imageiormeu on a small picture tube onto a trans-lucent screen. Optical distortion is compen-sated for by interposing a corrector lens in theprojection path.

scrambled speech. Radio -telephone speech thathas been made unintelligible to those not hav-ing the proper receiving equipment.

scratch filter. A filter circuit used in connectionwith a phonograph pickup to block those fre-quencies at the higher end of the audio rangeat which needle scratch is most prominent.

screen. The surface of a cathode-ray tube uponwhich the visible pattern is produced. Also ashield.

screen grid. An electrode mounted between thecontrol grid and plate of a vacuum tube forthe purpose of reducing the capacity betweenthese two electrodes.

screen -grid modulation. Modulation produced byintroduction of the modulating signal into thescreen -grid circuit of a multi -grid tube inwhich the carrier is present.

screen -grid tube. A vacuum tube having a screengrid.

screen -grid voltage. The de voltage applied be-tween the screen grid and the cathode of avacuum tube to make the screen grid positivewith respect to the cathode.

screen persistence. The property of the fluorescentscreen of a picture tube to continue the radia-tion of light for a short time after the electronbeam causing the light spot has passed.

seal -disc tube. A tube in which the grid is a por-tion of a disc, sealed into the glass envelope.See lighthouse tube.

sealing compound. Wax or pitch used in condenserblocks and transformer housings to preventair and moisture from reaching the parts.

sealing off. Final closure of the glass or metalenvelope of a vacuum tube or lamp afterevacuation.

search coil. A tiny exploring coil of wire usedwith a ballistic galvanometer or fluxmeter tomeasure flux density in a magnetic field.

secant (sec). A trigonometric function. Thesecant of an acute angle of a right triangle(written sec 0) is equal to the hypotenuse di-vided by the adjacent side. The secant is thereciprocal of the cosine.

second anode. The electrode in a cathode-ray tubethat is maintained at a constant positive po-tential and used to accelerate the electronbeam.

secondary. A transformer winding that receivesenergy by electromagnetic induction from an-other or primary winding.

secondary cell. A dc voltage source capable ofstoring electrical energy. When exhausted, itcan be recharged by sending direct currentthrough it in the reverse direction. Each cellof an ordinary storage battery is a secondarycell.

73

secondary electrons. Electrons emitted from abody due to the impact or bombardment ofother electrons.

secondary emission. Emission of electrons froman electrode when it is hit or bombarded byhigh-speed electrons.

secondary voltage. The voltage across the sec-ondary winding of a transformer.

secondary winding. See secondary.

second detector. The, stage of a superheterodynereceiver that separates the modulation fromthe intermediate frequency carrier signal.

sectoral horn. An electromagnetic radiator, twoopposite sides of which are parallel, and theremaining two sides of which diverge.

selective fading. Fading that is not the same atall frequencies.

selective interference. Radio interference concen-trated in a narrow band of frequencies. Someexamples are other radio stations on the sameor adjacent frequencies, or harmonics of otherradio stations.

selective reflection. Reflection of waves of only acertain group of frequencies.

selectivity. The degree to which a receiver Iscapable of reproducing signals of one stationwhile rejecting signals from all other stationson adjacent channels.

selectivity control. The device or circuit thatchanges the selectivity of a receiver.

selector. A device, mechanical, electronic, or elec-trical, for making connections to any one ofa number of circuits at will.

selector switch. See selector.selenium cell. A photoconductive cell using some

form of selenium as the light-sensitive mate-rial. The resistance of the cell varies with theamount of light falling on the cell.

selenium rectifier. A dry -dish rectifier made of acrystalline selenium layer between two elec-trodes. A chemical barrier action between theselenium and one electrode produces a uni-directional current flow when ac voltage isapplied.

self -bias. See automatic grid bias.self-cleaning contacts. Contacts designed to close

with a rubbing motion that keeps them clean.self -excitation. Supplying of field current to a

generator from its own armature.self-excited oscillator. An oscillator that starts

itself. Any change in plate current will inducea voltage in a tank circuit, which changes thegrid voltage so that oscillations are developedand maintained.

self -healing capacitor. A capacitor that repairs it-self after dielectric breakdown.

self-inductance. The property that determineshow much electromotive force will be inducedin a coil or circuit by a change of current inthat same coil or circuit; often simply calledinductance.

self -modulated oscillator. See blocking oscillator.self -quenched detector. .A super -regenerative de-

tector in which the time constant of the gridleak and grid capacitor is sufficient to causeintermittent oscillation above audio frequen-cies, stopping normal regeneration each timebefore it becomes squealing.

Selsyn motor. A synchronous motor that accurate-ly follows the phase of the voltage fed to it.

semi -conductors. Materials characterized by com-paratively high resistivities. Many of theseare salts or oxides in which conduction is ionic.Another group, more important in communica-tions, are semi -metallic elements or oxides inwhich conduction is electronic.

sending. Transmitting, as Morse code.

sense antenna. A non -directional antenna usedwith a direction finder to cause reception tobe unidirectional rather than bidirectional.

sense finder. The portion of a radio directionfinder that determines which of two oppositedirections (180° apart) a radio wave is com-ing from.

sensitive relay. A relay requiring very smallamounts of current for operation.

sensitivity. A measure of the ability of a receiverto reproduce weak signals with satisfactoryvolume. The smaller the input necessary togive a standard test output, the higher thesensitivity.

sensitivity control. A device that governs the gainof the rf or i-f amplifier stages of a receiver.

sequential system. A system of color televisiontransmission in which the colors are trans-mitted one after the other and which dependson eye retention and picture tube storage tocombine them.

series. An arrangement of parts In such a waythat the same current flows through all ofthem.

series connection. A connection in which the samecurrent must flow through all of the series -connected parts.

series feed. Application of a do operating voltagethrough a circuit carrying a signal current.

series modulation. Modulation in which plate cir-cuits of the modulating tube and the modu-lated amplifier tube are in series with theplate voltage supply.

series peaking. The use of an inductance in serieswith the plate of a video amplifier tube tocompensate for loss of high -frequency gainand to correct high -frequency phase shift.

series resonant circuit. A circuit in which a coiland condenser are connected in series withthe source of voltage, or in which the excitingvoltage is induced in the coil, and where theinductive reactance of the coil is equal to thecapacitive reactance of the condenser at thedesired resonant frequency.

serrated pulse. In television, a vertical synchron-izing pulse divided into a number of smallpulses that act for only half a line.

serrated rotor plate. A variable condenser rotorplate having slots cut along its edge to dividethe plate into sections that can be bent in orout to adjust the capacity during alignment.

service area. The region around a station inwhich its signal strength is strong enough toinsure satisfactory reception at all times.

service band. A band of frequencies allocated toa given class of radio -communication service,such as the broadcast band, a police band. etc.

serviceman. A radio repairman or radio technician.

service oscillator. A test instrument used to gen-erate radio -frequency oscillations for align -Merit and test purposes.

74,

sesqui-sideband transmission. The transmission ofa carrier with one full sideband and half ofthe other. See vestigial sideband.

set analyzer. A test instrument for measuringvoltages and currents in electronic equipment.

set-up. The Initial adjustment of a receiver ortransmitter before it is placed in service.

shaded -pole induction motor. An Induction motorutilizing field displacement caused by a smallcoil wound around a part of one field pole forinitiating rotation.

shading ring. A large copper ring placed aroundthe central pole piece of a loudspeaker fieldmagnet to act as a shorted turn and buck outhum voltages. Also called shading coil, andused on part of one pole of small ac motors toproduce a rotating magnetic field.

shading signal. . signal that raises the gain ofthe amplifier of a television camera for thoseintervals of time when the electron beam isin a dark -spot area. .

shadow tuning indicator. A tuning meter having asmall square metal vane mounted on a shaft,which in turn is connected to a meter move-ment. A pilot lamp is mounted behind the vaneso that a shadow is thrown upon a glass screen.The meter is so constructed and connectedinto a radio receiver circuit that the shadowwill be narrowest when the receiver is accu-rately tuned to a station.

shank. The portion of a phonograph or record-ing needle that is clamped into position by aset -screw in the pickup or cutting head.

sharp. A term usually used to describe the selec-tivity of a circuit that will respond to a verylimited range of frequencies or to a singlefrequency only.

sheath. The external conducting surface of ashielded transmission line. Also, the metal wallof a wave guide.

shell -type transformer. A transformer whose ex-ternal metal covering resembles a shell or adish, and whose core has three legs, with thecoils wound on the center leg. Contrasted withthe core type which has the form of an "O"with coils wound on both sides.

Serrated Rotor Plates

shield. A metal can or housing placed around apart, wire, or circuit to prevent its electricand magnetic fields from affecting nearbyparts or to prevent qther fields from affectingIt.

shielded line. A transmission line having an ex-,ternal conducting surface (a sheath or shield)that confines the signals to the space withinthe shield or prevents pickup of undesired sig-nals by the line.

shielded pair. A two -wire transmission line sur-rounded by a metal sheath.

shielded wire. Insulated wire having around it ashield of tinned, braided copper wire.

shielding. Metal covering used on a wire, or the

metal can, partition, or plates used aroundparts to prevent undesirable radiation, pickupof signals, magnetic induction, stray current,or ac hum.

shock excitation. Production of oscillations in anoscillatory circuit by a sudden electrical dis-charge or pulse.

shoran. (Coined from SHOrt RAnge Navigation.)A system for determining distance from fixedknown points by measuring the time takenfor a pulse signal to travel from the airplaneto a receiver -transmitter at the fixed point andreturn.

short circuit. An undesirable current path, occur-ring accidentally or because of a part break-down, that exists between the two sides of acircuit or between any two circuit terminals.

shorting contact switch. A rotary selector switchin which the width of the movable contact isgreater than the distance between contactstuds, so the circuit is never completely open.Also called a make -before -break switch.

short-wave converter. A radio device that can beconnected between a broadcast receiver andits antenna system to convert high -frequencysignals to a broadcast -band frequency that canbe handled by the receiver.

short waves. Wavelengths shorter than those in-cluded in the broadcast band, hence wavesshorter than 200 meters. Short waves corre-spond to frequencies higher than the highestbroadcast -band frequency of 1600 kilocycles.

short-wave transmitter. A radio transmitter thatradiates short waves.

shot effect. The uneven or non -uniform impact ofelectrons on the plate of a vacuum tube, whichshows up as noise in a sensitive amplifier.

shunt. A resistor placed across the terminals ofan ammeter to allow a definite part of thecircuit current to go around the meter. Also,any parallel -connected part, or the act of plac-ing one part in parallel with another.

shunt feed. The application of a de operating volt-age through a circuit parallel to and separatedfrom the signal circuit. Parallel feed.

shunt peaking. The use of an inductance in . aparallel circuit branch of a video amplifier tocompensate for the high -frequency loss due tothe shunt circuit capacitance or to correct thehigh -frequency phase shift.

shunt-wound. A motor or generator wound so thearmature and field are in parallel.

shutter. A device for cutting off light.sideband. A band of frequencies on either side of

the carrier frequency of a modulated radiowave.

sldeband attenuation. Attenuation in which thetransmitted amplitude of some component orcomponents of a modulated signal (excludingthe carrier) is smaller than that produced bythe modulation process.

side frequency. A frequency on either side of thecarrier frequency, a component of a sideband.

sign. A symbol used to indicate a particular op-eration in arithmetic, algebra, or mathematicsin general. Examples: +, X. -÷, =. Alsocharacters indicating polarity and positive andnegative numbers.

signal. A radio wave or alternating current thatcarries intelligence of any form.

signal generator. A test instrument used to pro-duce a modulated or unmodulated rf carrier

75

signal having a known radio -frequency value,sometimes also at a known voltage.

signalnoise ratio. See signal-to-noise ratio.signal plate. The metal plate on the back of the

mica sheet supporting the mosaic of one typeof cathode-ray television camera tube. A ca-pacity exists between each globule and thisplate, and as each globule loses electrons, theeffect is relayed electrically to the signal platethrough the mica dielectric.

signal -shifter. A variable -frequency rf exciter oroscillator intended chiefly for amateur trans-mitters.

signal strength. A measure of the signal level ata particular location, usually expressed asmillivolts per meter of effective height of thereceiving antenna.

signal -strength meter. A meter connected in theavc circuit of a receiver and calibrated in dbor arbitrary units to indicate the strength ofa received signal.

signal-to-noise ratio. The ratio of the intensity ofa desired signal at any point to the intensityof noise signals at that same point.

signal tracer. A test instrument designed to in-dicate the presence of signals at any point ina receiver.

signal tracing. A receiver servicing technique thatinvolves tracing the progress of a signalthrough an entire receiver, stage by stage,while the receiver is in operation. Measure-ments made during this procedure by a signaltracer indicate when the defective part orstage has been reached.

signal wave. A wave that conveys a signal.

silent period. A period during each hour in whichship and shore radio stations must remainsilent and listen for distress calls.

silk -covered wire. Wire insulated with one ormore layers of silk.

simplex operation. Operation of a telegraph orradio system in only one direction at a time.

simultaneous transmission. A system of color tele-vision transmission in which all three primarycolors are transmitted at the same instant overseparate channels, and are superimposed oneover the other at the receiver.

sine (sin). A trigonometric function. The sine ofan acute angle of a right triangle (writtensine 9) is equal to the opposite side dividedby the hypotenuse.

sine wave. The wave form of a single -frequencyalternating current. A wave whose displace-ment is the sine of an angle proportional totime, or distance, or both.

singing. An undesired self -sustained oscillation.singing point. The adjustment of gain or phase

or both, at which singing will start.single -button carbon microphone. A microphone

having a carbon -filled button on only one sideof its diaphragm.

single -dial control. Tuning in a station by meansof a single control that is mechanically linkedto all tuning condensers or tuning inductancesin the set.

single ended. Using a single tube or tubes con-nected in parallel rather than in push-pull.

singleended stage. An amplifier in which onlyone tube is normally used, or, if more than onetube is used, they are connected in parallelso that operation is not balanced with respectto ground.

single -ended Tube. A tube with all grid connectionson the base (no top cap).

single phase. A circuit or device that is energizedby a single alternating voltage. Also, one ofthe phases of a polyphase system.

single -pole switch. A toggle or knife switch hav-ing only one movable contact arm or blade.

single-sideband transmission. A method of broad-casting in which one sideband is transmittedbut the other sideband is suppressed. The car-rier wave may be either transmitted or sup-pressed.

single -signal receiver. A superheterodyne receiverequipped with a crystal filter usually locatedin the intermediate -frequency amplifier to pro-vide single -frequency (code) reception. Alsoa set designed to receive only one station.

single -throw switch. A toggle or knife switch ofthe ON -OFF type, capable of closing or open-ing only one circuit for each blade of theswitch.

sink. Term sometimes used by telephone engi-neers to designate a load or power -consumingdevice.

sinusoidal. Having a sine -wave form.

skew. Distortion produced by a facsiniile recorderdue to lack of synchronism between scannerand recorder.

skin effect. The tendency of a high -frequencycurrent to flow near the surface of the con-ductor, rather than through the entire cross-section of the conductor. This decreases theuseful diameter of the conductor, so it acts asif it has more resistance than it does to dc.

skip distance. Distance between the transmittingantenna and the nearest point at which thereflected sky wave comes back to earth.

skip zone. A ring -shaped region around a trans-mitter within which there is no reception fromthe transmitter except that from ground waves.The outer edge of the ring is fixed by the skipdistance.

sky waves. Radio waves that travel up into thesky from the transmitting antenna, some ofwhich are reflected back to earth by the Ken-nelly -Heaviside ionized layer.

sleeve. The cylindrical metal contacting partimmediately back of the tip in a telephone- orradio -type plug. Also, the insulating jacketthat fits over the cone of metal -cone televisionkinescopes. Also, insulating tubing or spa-ghetti, used as a sheath over wire.

slide. A title or picture mounted for transpar-ency projection.

slider. A sliding type of movable contact.slide rule. A device consisting of sliding ruler -

like scales and a movable indicator, arrangedto give a convenient mechanical equivalent ofa table of logarithms. It is used for perform-ing the operations of multiplication, division.squaring, cubing, extracting square roots, anddetermining trigonometric functions.

slide -rule dial. A tuning dial used on receivers, inwhich a vertical marker moves horizontallyover long straight scales resembling the scalesof a slide rule.

slip. The difference between synchronous andactual speed in an induction motor.

slip rings. The rings of an ac motor or generator,corresponding to the commutator of a dc motoror generator, through which connection ismade to the rotating member of the device.

76

slot antenna. A radiating element formed by aslot in a metal surface.

slow -acting relay. A time delay relay in which anadjustable interval of time exists between en-ergizing or de -energizing of the coil and at-traction or releasing of the armature.

slow -release relay. A relay in which there is anappreciable delay between de -energizing of thecoil and release of the armature.

slug. A brass rod or powdered -iron core used inan rf coil. Also, a heavy metal ring or short-circuited winding placed on the core of a relayto give a time delay in its operation.

slug tuning. Varying the frequency of a resonantcircuit by introducing a slug of material intoeither the electric or magnetic fields or both.

smear ghost. A spurious image caused by a num-ber of multiple reflections.

S meter. See signal strength meter.smoothing choke. An iron -core inductor used in a

filter to remove pulsations in the unidirec-tional output current of a rectifier or direct -current generator.

smoothing filter. A filter composed of Inductanceand capacitance for removing ac componentsfrom the unidirectional output current of arectifier or direct -current generator.

snap switch. A switch in which the contacts areseparated or brought together suddenly by theaction of a spring placed under tension or com-pression by the operating knob or lever.

snow. Television slang for the effect of randomnoise on the reproduced picture. It has theappearance of a grainy, speckled pattern super-imposed on the picture.

socket. A mounting device for tubes, plug-incoils, plug-in condensers, plug-in resistors, andcrystals, having holes with spring clips ar-ranged to fit and grip the terminal prongs ofthe part being plugged in. Also, a bayonet orscrew -type socket for pilot lamps.

soft tube. A vacuum tube in which a small amountof gas is allowed to remain when the bulb isevacuated.

solder. An alloy of lead and tin that melts at afairly low temperature and is used for makingpermanent electrical connections between partsand wires.

soldering gun. A soldering iron resembling apistol. It has a fast -heating resistance elementat the tip, that operates at high current andlow voltage from a step-down transformerbuilt into the unit.

Colo Icso

Soldering Gun

vat cr .11f II. Co.

soldering iron. A device used to apply heat to ajoint to be made permanent by soldering.

soldering pencil. A soldering iron with a thinbarrel and tip for soldering in small spaces.

solderless connections. Wiring connections madeby the use of small screw clamps that firmlyhold the wires to be joined.

solenoid. An electromagnet having a movableiron core.

solid conductor. A single wire. A conductor thatis not divided into strands.

sonar. (Coined from SOund Navigation AndRanging.) A system for determining the di-rection and position of an object by means ofreflected sound waves.

sonic. Pertaining to or utilizing sound waves.sound. A general term used to specify a sound

wave (a traveling vibration in air or someother elastic medium) or a sound sensation(the effect of this sound wave on human ears).Sound is sometimes defined as a vibration of abody or material at a rate that can be heardby human ears. The extreme limits of humanhearing are 20 cycles and 20,000 cycles, butanimals can hear still higher frequencies. Batscan hear sound waves as high as 50,000 cycles.Sound can travel through any medium that canvibrate; the resulting traveling vibrations arecalled sound waves.

sound analyzer. An electronic apparatus, such asan oscilloscope, harmonic analyzer, or audio-meter, used to measure sound levels andanalyze frequency components in an audiosignal.

sound carrier. The television signal carrier thatconveys the audio part of the signal.

sound effects. Life -like sound imitations producedby various devices or recordings.

sounder. A telegraph receiving instrument.sound gate. The mechanism through which sound

motion picture film passes for the purpose ofconverting the sound track on the film intoaudio signals.

sound Intensity. The sound energy transmitted perunit of time in a specified direction through aunit area perpendicular to this direction. Itis expressed in ergs per second per squarecentimeter or in watts per square centimeter.Also called flux density or sound -energy fluxdensity.

sound -level meter. An instrument for measuringsound intensities electrically, having an out-put indicator calibrated in db or directly inunits of sound intensity.

sound panel. Movable panels of rock wool forsound absorption, or hard surfaces for reflec-tion.

sound -powered telephone. A telephone operatingentirely on current generated by the speak-er's voice, requiring no batteries or powersupply. A diaphragm, activated by soundwaves, moves a small coil through a magneticfield, producing a current in the coil.

sound pressure. The effective (rms) value of thesound pressure, measured in dynes per squarecentimeter.

sound sensation. The sensation produced in thehuman ear by a sound wave.

sound track. A recording of sound on film or onsensitized paper for reproduction.

sound wave. A traveling wave produced by vibra-tion of an elastic medium (air, metal, wood,etc.) at a rate that can be heard.

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source. The part supplying electrical energy orradio signals to a circuit.

south pole. The pole of a magnet at which themagnetic lines of force enter.

space charge. The electrons accumulated in thespace between the cathode and plate of a vac-uum tube, usually close to the cathode.

space -charge effect. The repulsion exerted onelectrons emitted from the cathode of a vac-uum tube by electrons accumulated in spacenear the cathode.

space -charge grid. A grid located next to thecathode and made positive with respect to thecathode, for the purpose of controlling thespace charge.

space cloth. Carbon -impregnated cloth used as awaveguide termination.

space current. The current made up of electronsmoving from the cathode to the plate and theother positive electrodes in a thermionic vac-uum tube.

spacing wave. In telegraphic communication, theemission that takes place in between the codecharacters or when no code characters are be-ing transmitted.

spaghetti. Heavily varnished cloth or plastic tub-ing sometimes used to provide additional in-sulation for wires.

spark. A momentary flash due to an electric dis-charge through air or some other dielectricmaterial.

spark coil. An induction coil used to producespark discharge.

spark frequency. The number of sparks occurringper second in a spark transmitter.

spark gap. An arrangement of electrodes acrosswhich a spark will jump at a predeterminedvoltage.

spark -gap modulation. A modulation process thatproduces one or more pulses of energy bymeans of a controlled spark -gap breakdownfor application to the element in which modu-lation takes place.

sparking. Intentional or accidental spark dis-charges, as between the brushes and com-mutator of a rotating machine, or betweencontacts of a relay or switch.

sparking voltage. The minimum voltage at whicha spark discharge occurs. Also, the startingpotential of a cold -cathode gas tube.

spark transmitter. A radio transmitter using theoscillatory discharge of a condenser througha coil and a spark gap as the source of its rfpower.

speaker. See loudspeaker.specific gravity. The weight of a substance as

compared to the weight of an equal volumeof water.

specific inductive capacity. Another name for di-electric constant, the ratio of condenser ca-pacity with a given dielectric to the capacityof a similar condenser with air as the dielec-tric.

specific resistance. The resistance of a unit con-ductor having a cross-sectional area of 1 cir-cular mil and a length of 1 foot, a circular -mil -foot. Also called resistivity.

spectrum. All frequencies used for a particularpurpose. Also, any series of radiant energies(or light), arranged in order of wave length.

spectrum analyzer. A -device for sweeping over a

spectrum or band of frequencies to determinewhat frequencies are being produced, and theamplitudes of each such component.

speech amplifier. An audio amplifier.

speech clipper. An electronic circuit for the pur-pose of limiting the wave crests of speech fre-quency signals.

speech -frequency range. Audio frequencies fromabout 100 to 3000 cycles. In audio equipment,the frequency range necessary for intelligiblespeech.

speech inverter. See scrambled speech,.

spherical. Having the form of a ball or sphere.spherical aberration. A lens defect in which the

light rays coming from a single point arebrought to different focal points by the edgesof the lens.

spherical wave. A wave whose wave front is aspherical surface.

spider. A highly flexible fiber ring that serves tocenter the voice coil of a dynamic loudspeakerbetween the pole pieces and at the same timeprovide a restoring force, causing the voicecoil to return to the same starting point aftereach movement. Also, a small metal cap usedto couple the driving pin to the apex of thecone in magnetic speakers.

spike. A spurious pulse of relatively short dura-tion, superimposed on the main pulse. Seeovershoot.

WESTERN UNION SPLICE

Splices

BELL SPLICE

splice. A joint between two wires that possessesmechanical strength as well as electrical con-ductivity.

split -anode magnetron. A magnetron in which thecylindrical anode is divided longitudinally intohalves, between which extremely high -fre-quency oscillations are produced.

split rotor plate. See serrated rotor plate.split -stator variable capacitor. A variable capaci-

tor having a rotor section that is common totwo separate stator sections.

sporadic E layer. A portion of the normal E layerof the atmosphere that sometimes breaks awayand exhibits special characteristics.

sporadic reflections. Sharply defined reflections ofsubstantial intensity from an ionized layer ofthe ionosphere at frequencies greater than thecritical frequency of the layer. They are ex-tremely variable in respect to time of occur-rence, geographic distribution, and frequencyrange.

spot. The luminous area produced on the view-ing screen of a cathode-ray tube by the elec-tron beam.

spot speed. The product of the length of scanningline and the number of scanning lines persecond in a facsimile system.

spottiness. The effect in a television picture re-sulting from variations in the instantaneouslight value of the reproduced image due to

78

electrical disturbances between the scanningand reproducing devices.

spreader. The insulating cross -arm used to spaceaerial wires when more than one wire is used.

spring contact. A relay or switch contact mountedon a spring, usually of phosphor bronze.

spurious radiation. Any emission from a radiotransmitter at frequencies outside its assignedcommunication band.

spurious response. A condition wherein a receiveris resonant at one or more frequencies otherthan that to which it is tuned.

square. The product obtained by multiplying anumber by itself. Example: 49 is the squareof 7, because 7 X 7 = 49.

square -law detector. A detector whose output cur-rent is proportional to the square of the rfinput voltage.

square -loop antenna. An FM antenna consisting offour dipoles arranged in the form of a square.

square mil. The area of a square whose sides are.001 inch (one mil).

square root: A number which, when multiplied byitself, equals a given number. Examples: 2is the square root of 4; 13 is the square rootof 169.

square wave. The waveform of a quantity thatshifts abruptly from one to the other of twodefinite values, giving a square or rectangu-lar pattern when amplitude is plotted againsttime.

squealing. A condition in which a high-pitchednote is heard along with the desired radio pro-

. gram. It can be due to interference betweenstations.

squegging oscillator. (Pronounced to rhyme with"dredging.") See blocking oscillator.

squelch. To automatically quiet or reduce the' output signal of a receiver when the applied

input signal strength is less than a certainvalue.

squelch circuit. An ave circuit that reduces thenoise otherwise heard in a radio receiver be-tween signals by blocking some stage whenthe signal amplitude is below a value calledthe squelch level.

SS loran. A loran system synchronized by skywaves instead of ground waves.

stability. Freedom from oscillation.stabilized feedback. Another term for negative

feedback, degeneration, or inverse feedback.stacked array. An array in which half -wave an-

tenna elements are placed one above the other.stacked dipoles. Two or more dipole antennas

arranged one above the other on a vertical sup-porting structure.

stage. A circuit containing either a single tubeor two or more tubes connected in push-pull,push -push, or parallel.

stage -by -stage elimination method. A method ofservicing receivers similar to the circuit dis-turbance method except that the test signalis introduced by means of a test oscillator.

stage efficiency. The ratio of useful power de-livered to the load (ac) and the plate powerinput (dc).

staggered tuning. Interstage coupling circuits of avideo i-f amplifier are said to be staggered whenthey are tuned to different frequencies within

a desired pass band. Staggered tuning is usedto give broadband response.

standard de -emphasis characteristic. The amountof de -emphasis necessary to correct standard-ized pre -emphasis. In FM, a response, decreas-ing as the modulating frequency increases, ata rate equal to that provided by a simple R -Ccircuit having a time constant of 75 micro-seconds.

standard pre -emphasis characteristic. A standard-ized amount of pre -emphasis. Especially inFM, a response, increasing as the modulatingfrequency increases, at a rate equal to thatprovided by a simple coil -resistor circuit inthe modulating source having a time constantof 75 microseconds.

standard test output. The output power into astandard dummy load at which a receiver istested. For receivers that can produce morethan 1 watt of undistorted output power, it is..5 watt. For receivers that can produce nomore than 1 watt, it is .05 watt.

standing wave. The wave -like distribution ofvoltage or current along a transmission lineas the result of the interaction between thewave from the source and the one reflectedfrom the load, when there is a mismatch atthe load end of the transmission system.

standing wave ratio (SWR). The ratio of the volt-age maximum to the voltage minimum along atransmission line.

stand-off insulator. An insulator used to support awire at a desired distance away from the sup-port on which the insulator is mounted.

starting anode. An electrode used to establish theinitial arc or to prevent extinction in a mer-cury -arc rectifier or similar tube.

static. Interfering noises heard in a receiver dueto waves created by atmospheric electrical dis-turbances such as discharges of lightning.

static characteristic. The characteristic of a tubewhen supplied only with dc operating voltages(no signal voltages).

static charge. An electric charge accumulated onan object, usually by friction.

static eliminator. A device designed to attenuatethe effect of static interference in a receiveror other electronic equipment.

static machine. A machine for generating electriccharges.

station. An assembly of radio transmitting equip-ment and its transmitting antenna.

stationary wave. See standing wave.station selector. The switch or tuning element

in the receiver used to select the desired signal.stator. The fixed set of plates in a variable con-

denser. Also, the non -rotating part of an elec-tric motor or generator.

steady state condition. Normal operation reachedby a device after the transients produced asa result of turning it on have died out.

steatite. Soapstone talc. A mineral consistingchiefly of a silicate of magnesium, with ex-cellent insulating properties.

step-down transformer. A transformer in whichthe secondary winding has fewer turns thanthe primary, so that the secondary delivers alower voltage than is applied to the primary.

step-up transformer. A transformer in which thesecondary winding has more turns than theprimary, so that the secondary delivers ahigher voltage than is applied to the primary.

79

storage battery. One or more secondary or stor-age cells connected together, usually in series.

Courtesy Exide

Storage Battery

storage cell. A secondary cell. More specifically,one of the cells in the ordinary storage bat-tery, capable of being recharged.

storage -type camera tube. A television cameratube on which the elemental areas on thephotosensitive plates build up their chargesgradually, developing a picture signal propor-tional to the time of charging of the plates bylight from the scene.

straight-line characteristic. Any action that canbe represented by a straight line on a lineargraph, that is, when one quantity varies indirect proportion to another.

strain. The change of shape, size, or form causedby applied force.

strain insulator. An insulator designed to with-stand the tension in a guy wire, antenna, orother stretched wire, used to break up thewire into insulated sections.

strand. One of the small wires in a group of wirestwisted or braided together.

stranded wire. A number of small wires twistedor braided together and used as a single con-ductor.

stray capacity. Capacity that exists betweenparts, between wires, or between a chassis andvarious parts and wires.

stray field. Stray inductance. Leakage magneticflux that spreads outward from an inductorand does no useful work.

streaking. In television, a broad streak follow-ing an outline representing a sharp change inshade from light to dark or vice versa. Thestreak is intermediate in shade and is causedby inability of the system to reproduce thechange as rapidly as necessary.

stress. The force that opposes a displacement ordistortion in the shape of a substance.

striking potential. The grid potential of a gas -filled triode at which plate current begins flow-ing.

stroboscope. An instrument used to permit visualinspection of vibrating or revolving objectsby illuminating them periodically, as theyreach the same definite points in their rota-tion or recurring movement.

Or -abaft -on. A glow lamp that is made to produceaccurately timed flashes of light that permitvisual inspection of high-speed moving parts.

stub. A shorted or open impedance path betweenthe two conductors of a transmission line orin a wave guide. It is adjustable as to posi-tion so as to match the impedance of an an-tenna or transmitter to that of a transmis-sion line. Also, a quarter -wave length of trans-mission line used between a transmission lineand either its source or load, used for imped-

ance matching by making connections at theproper points along its length. Also, an openquarter wave or shorted half wave length oftransmission line, connected across the an-tenna terminals of a receiver so as to act as ashort circuit at the frequency of an interfer-ing station.

studio. A room in which programs originate.

stylus. A specially shaped needle used to cutgrooves and record sound waves in wax or pre-pared record blanks.

stylus drag. The effect of the friction between therecord surface and the reproducing stylus.

stylus force. Effective weight of the reproduceror the force in the vertical direction on thestylus when in operating position.

subcarrier. An intermediate wave modulated byfacsimile signals and in turn used to modu-late the main carrier, either alone or in con-junction with subcarriers for other channels.

subharmonic. A frequency that is a fraction of thefundamental frequency. Thus, the second sub -harmonic is 1/2 the fundamental frequency;the third subharmonic is 1/3, etc.

subject copy. The material in graphic 'form to betransmitted in facsimile reproduction.

subscript. A small number or letter written at theright of and below another letter, for dis-tinguishing purposes. Example: In XL and Xc,the subscripts L and C serve to distinguishinductive reactance (XL) from capacitive re-actance (Xc); in R = Rl + R2 + R3 + R4,numeral subscripts serve to distinguish differ-ent resistor values. Xr, is pronounced "X subL" ; R3 is pronounced "R sub three" or "Rthree."

subtraction. The process of finding the numericaldifference between two quantities or numbers.

super. Popular name for superheterodyne re-ceiver.

superaudible. Having a frequency above approxi-mately 20,000 cycles per second, beyond nor-mal hearing range. Also called supersonic.

superaudio frequency. A sound -wave frequencyabove 20,000 cycles per second.

super -control tube. See variable -mu tube.superhet. Popular name for a superheterodyne

receiver.superheterodyne receiver. A radio receiver in

which the incoming modulated rf signal ismixed with a local oscillator signal in a fre-quency converter section where it is convertedinto a fixed, lower frequency signal called theintermediate -frequency signal of the receiver.This modulated i-f signal is given very highamplification in the i-f amplifier stages, thenfed into the second detector for demodulation.

super high frequency (shf). A frequency in theband between 3000 mc and 30,000 mc.

superimpose. To put one over another, as tele-vision images, in such a way that they mayboth be seen, intermingled.

super -regenerative detector. A form of regener-ative detector in which the feedback is pe-riodically reduced by a quenching frequencyto prevent oscillation and still maintain highsensitivity.

super -sensitive relay. A relay that operates on acurrent value less than about 250 microamperes(1/4 ma).

supersonic frequency. A frequency above theaudible range.

80

supersonic vibrations. Vibrations that cannot beheard by the unaided human ear because theyare above the audible frequency range.

supply. A voltage source.

suppressed carrier transmission. A system of trans-mission used in telephony in which the car-rier component of the modulated wave is sup-pressed, only the side frequencies being trans-mitted.

suppressor. A resistor inserted in series with thespark -plug lead or the distributor lead of anautomobile engine to suppress spark inter-ference that might otherwise interfere withreception of radio programs in the auto radioset. Also, a resistor or choke coil used in aradio circuit to suppress oscillations.

suppressor grid. A grid placed between the screengrid and the plate of a vacuum tube and main-tained at or near cathode potential, in orderto force secondary electrons back to the plate.

surface defects. Defects readily visible on top ofthe radio chassis or in the connections to aradio, such as: tube top cap off; disconnectedantenna lead-in; a dead tube, etc.

surface leakage. A leakage of current over thesurface of insulation.

surface noise. The noise reproduced in playing arecord due to rough particles in the recordmaterial and/or irregularities in the walls ofthe groove left by the cutting stylus.

surge impedance. The impedance in ohms at theinput of an infinitely long line, or of a prac-tical line with its far end closed by a match-ing impedance. It is equal to VL/C of theline for all but very low frequencies. Alsocalled characteristic impedance.

surges. Sudden increases of current in a powerline or circuit.

susceptance. The reciprocal of reactance.sweep. The motion of an electron beam over the

screen of a cathode-ray tube.sweep circuit. An oscillator circuit that generates

a voltage having a sawtooth waveform suit-able for making the electron beam of a cath-ode-ray tube sweep across or up and down thefluorescent screen.

sweep generator. A generator of a radio -frequencysignal, the frequency of which varies aboveand below the mean frequency at a rapid andconstant rate.

sweep voltage. The periodically varying voltageproduced by a sweep oscillator.

swinging. A momentary variation in the freqeuncyof a radio wave.

swinging arm. A mounting and feed used to movethe cutting head at a uniform rate across therecording disc in some sound recorders.

swinging choke. An iron -core choke operated withan almost saturated core, in order to make theinductance vary or swing as the average cur-rent changes.

switch. A device for opening and closing an elec-trical circuit, or for changing the connectionsbetween parts or circuits.

symbol. A simple design used to represent a parton a schematic diagram. Also. a letter used informulas to represent a particular quantity.

symmetrical. Balanced. Equal on each side of anormal or center line.

sync. See synchronizing.

sync clipper. A vacuum tube circuit that is biasedso as to remove the sync signals from thecomposite video signal.

sync generator. Electronic equipment designed toproduce the driving, blanking, and synchroniz-ing pulses necessary to the operation of atelevision system.

Synchroguide. A control circuit for horizontalscanning in which the sync signal, oscillatorvoltage pulse, and the scanning voltage arecompared and kept in synchronism.

synchronism. The state of being synchronous.synchronization. The process of causing to be

synchronous. Specifically, the process of keep-ing the image -reconstructing action of a tele-vision or facsimile receiver in step with thecorresponding action at the transmitter.

synchronized. In step With.

synchronizing. Causing two elements of a systemto coincide in speed, frequency, relative posi-tion, or time.

synchronizing generator. An electronic generatorthat supplies synchronizing pulses to televisionstudio and transmitter equipment.

synchronizing pulses. In television, the portions ofthe transmitted signal that control horizontaland vertical scanning of the receiver. Seehorizontal and vertical synchronizing pulses.

synchronizing separator. The circuit that separatesthe control pulses from the video signals.

synchronizing signals. Electrical pulses used tokeep a television or facsimile receiving systemin step with the transmitting system, so thatthe picture or scene will be reconstructedproperly.

synchronous. Simultaneous in action and in time(in phase).

synchronous condenser. A synchronous motor thatis over -excited so that it produces a leadingcurrent, used to correct power factor whereinductive loads are across the power line.

synchronous switch. A circuit in which thyratronscontrol the operation of ignitrons in such ap-plications as resistance welding.

synchronous vibrator. A vibrator that serves thedual function of converting a low de voltage toa low ac voltage and at the same time rectify-ing a high ac voltage.

sync inverter. A vacuum tube circuit that pro-duces a phase shift of 180° of the sync pulsesto provide the necessary polarity for control

. of the scanning oscillator.sync limiter. A vacuum tube circuit that pro-

duces sync pulses of uniform height.sync segregator. The circuit used to separate the

norizontal from the vertical sync pulses.sync separator. See sync clipper. Also, a sync

segregator.synthesis. The building up of a whole out of

parts or elements, as a complex waveform bysuperimposition of harmonics on a fundamen-tal frequency.

table model receiver. A receiver having a cabinetof suitable shape and size for placing on atable.

tachometer. An instrument for measuring rota-tional speed in revolutions per minute.

81

talk -listen switch. A switch used In intercom-munication systems to enable the operator touse the receiving loudspeaker as a microphone.

tandem. See cascade.tangent (tan). A trigonometric function. The

tangent of an acute angle of a right triangle(written tan 0) is equal to the opposite sidedivided by the adjacent side.

tank circuit. An L -C resonant circuit capable ofstoring electrical energy at its resonant fre-quency.

T antenna. A fiat -top antenna, the lead-in ofwhich is taken from the center of the hori-zontal portion.

tantalum. A refractory metal possessing theproperty of absorbing gases, used for gridsand plates of power tubes.

tap. A connection made somewhere along an inductance or resistance, other than at the ends.

toper. Distribution of resistance over the rangeof rotation of a volume or tone control.

tape recorder. An electronic instrument for therecording and playing back of sound. An audio -modulated magnetic field influences the mag-netization of particles of iron in a movingpaper or plastic tape in accordance with theamplitude of the audio frequency signal. Forplayback, the tape is moved between the polesof the playback device, causing field fluctua-tions that can be amplified.

tape transmitter. A code -transmitting deviceactuated by pre -punched paper tape.tapped control. A volume or tone -control poten-

tiometer having a fixed tap somewhere alongthe resistance winding for the purpose ofproviding fixed bias or automatic bass com-pensation.

tapped resistor. A fixed resistor with extraterminals along the resistance element to pro-vide various voltage values needed in voltage -divider applications.

tap switch. A multipoint switch.

target. The electrode that collects electrons ina Farnsworth television dissector tube. Also,the fluorescent screen in a tuning -eye tube.

tearing. An undesirable effect in a received tele-vision picture in which groups of lines aredisplaced, giving the appearance of a tornpicture. Caused by unstable horizontal syn-chronization.

telautograph. A device that converts handwritinginto electrical impulses at the transmittingposition, and back to handwriting at the re-ceiving position.

telecamera. A television camera.telecast. A television broadcast.telecine protector. A device used to televisemotion -picture film.telegenic. Of a subject or model, suitable fortelevision.

telegraph -modulated wave. A continuous wave thatis varied in amplitude or frequency by meansof telegraphic keying.

telegraph sounder. A telegraph receiving devicethat converts code signals into sounds.

telegraphy. Communication by code signals sentby electrical or electronic means, with or with-out connecting wires.

telephone. A device containing a microphone for

converting sound waves into electrical signals,and an earphone receiver for producing soundfrom electrical signals.

telephony. An electrical method of reproducingsounds, especially those of the voice. at adistance.

telephotography. Radio or wire transmission ofstill pictures or photographs.

telephoto lens. A lens used to produce large pic-tures of an object quite distant irom thecamera.

Teletrician. A graduate of the National RadioInstitute, thoroughly trained in televisiontheory and service.

teletypewriter. A printing telegraph instrumenthaving a typewriter keyboard for sending mes-sages, and a motor -driven signal -actuatedmechanism for printing received messages di-rectly.

televise. To convert a scene or image into atelevision signal.

television. The transmission and reception of arapid succession of images of fixed or mov-ing objects by means of radio waves travelingthrough space or over wires.

television camera. In a television system, an as-sembly consisting of a pickup tube, sweepchains, preamplifier, and a means of focusingthe image on the pickup tube.

television channel. A band of frequencies 6 mewide, assigned to a television broadcast sta-tion.

television test chart. A chart placed before thecamera of the transmitter, having geometricpatterns that enable the observer to determinethe resolution and linearity of the receiver.

televisor. The scanning apparatus used in a me-chanical television system.

temperature coefficient. The change in character-istics of a substance for each degree Centigradechange in temperature.

temperature coefficient of resistance. The changeper ohm in the resistance of a given materialfor each degree of change in the temperature.

temperature -compensating condenser. A condenserused to compensate for reactance changes inoscillator circuits due to changes in tempera-ture, being designed to change in capacity inthe opposite manner so the reactance changewill be canceled.

temperature control. A relay actuated by a ther-mostat.

temperature relay. A relay that functions whenthe temperature of equipment associated withthe relay changes to a predetermined value.

temperature saturation. Also known as filamentsaturation. The condition in which increasingthe temperature of the cathode does not in-crease the plate current because the spacecharge forces the excess electrons to returnto the cathode as rapidly as they are emitted.

tension. Potential difference or voltage. Also, aforce causing or tending to cause extension.

term. A portion of an algebraic expression thatis separated from other parts by a plus orminus sign. Example: In the expression 17a2- 3a 2b2, the terms are 17a2, 3a, and21)2. Like terms have the same literal parts(the same letter combinations). Thus, the ex-pression 17a,x 6.7a.2x - 2aix contains alllike terms, and they can be combined by di-rect addition and subtraction to give 21.7a2x.Unlike terms contain different letter combina-tions, and cannot be combined directly by ad-

82

dition and subtraction. Example: 17ab81t, + 3x.

terminal. A point to which electrical connectionsare made.

terminal impedance. The impedance measured atthe input or output terminals of a device.

terminated line. A transmission line terminatedin the characteristic impedance of the line.

termination. The load connected to the output endof a transmission line.

Tesla coil. An air -core transformer having a fewturns of heavy wire as the primary and manyturns of fine wire as the secondary. The os-cillatory discharge across a spark gap appliedto the primary results in an extremely highvalue of high -frequency voltage across thesecondary, which is capable of producing abrush discharge between widely separatedelectrodes in air.

test board. A board or panel provided with in-struments, terminals, and equipment for test-ing electronic apparatus.

test lead. A flexible insulated lead used chieflyfor connecting meters and test instruments toa circuit under test.

test oscillator. A test instrument that will gen-erate an unmodulated or tone -modulated radio -frequency signal at a desired frequency. Alsocalled a signal generator or an all -wave signalgenerator.

Courtesy NBC

Television Test Pattern

test pattern. A geometric design periodicallytransmitted by a television station intended tofacilitate adjustment of a television receiver.

rest probe. See test prod.test prod. A sharp metal point provided with an

insulated handle and a means for connectingthe point to a test lead. It is used for makinga touch connection to a circuit terminal.

test set. A combination of instruments neededfor making a particular combination of testsor for servicing a particular type of electricalequipment.

tetrode. A four -electrode vacuum tube.TE waves. Transverse electric waves. Electro-

magnetic waves in a wave guide when theelectric field waves are transverse, and themagnetic field is in the direction of propaga-tion.

Theremin. An oscillator whose output frequencyand amplitude are variable, and are controlled

by capacity, changes, as by moving one's handswith respect to a rod or loop. An electronicmusical instrument.

thermal agitation. Tiny pulses of electron currentproduced by the random movement of freeelectrons in a conductor, due to heat.

thermal flasher. An electric device that opens orcloses a circuit automatically at regular inter-vals owing to alternate heating and coolingof a bimetallic strip.

thermal instrument. An instrument in which cur-rent is measured by sending it through a finewire, which is thereby heated, and the result-ing expansion or sag of the wire is used todeflect the meter pointer. Also called hot-wire instrument.

thermionic. Relating to electron emission underthe influence of heat.

thermionic emission. Emission of electrons froman electrode under the influence of heat.

thermionic tube. A vacuum tube in which thecathode is heated for electron -emitting pur-poses.

thermistor. A resistor element consisting ofmetallic oxides in inert binders, which havevery high negative temperature coefficients.

thermocouple. A pair of dissimilar conductors sojoined as to produce a voltage when the junc-tion is heated.

thermocouple ammeter. An ammeter dependent forits indications on the voltage produced in athermocouple when heated by the current tobe measured.

thermogalvanometer. An instrument for measuringsmall high -frequency currents by their heatingeffect.

thermometer. An instrument for measuring tem-perature.

thermopile. A unit consisting of a number ofthermocouples connected in series to increasethe voltage sensitivity.

thermostat. A device used to open or close circuitswith changes in temperature.

third harmonic. A sine -wave component having afrequency three times that of the fundamentalfrequency of a complex wave.

thoriated filament. A vacuum tube filament madeby compounding thorium and tungsten.

thorn needle. A soft playback point or phono-graph needle, such as a cactus or fiber needle.

thread: The material cut from a phonograph discby the recording stylus during recording. Alsocalled chip.

three -band receiver. A radio receiver having threedifferent tuning ranges.

three-phase current. Current delivered throughthree wires, with each wire serving as thereturn for the other two and with the threecurrent components differing in phase succes-sively by one-third of a cycle, or 120 electricaldegrees.

three -pole switch. An arrangement of three single -pole switches coupled together to make orbreak three contacts simultaneously.

three -wire system. A direct -current or single-phase alternating current system comprisingthree conductors, one of which (the neutralwire) is maintained at a potential midwaybetween the potential of the other two.

threshold. The point just at the verge of observa-tion by the senses or by an indicator, or the

83

point at which a circuit action will be initiated.threshold of audibility. The loudness level at which

sound is just barely heard.

threshold of feeling. The loudness level at whichsound is felt rather than heard.

throat microphone. A contact microphone that isstrapped to the throat and operated by throatvibrations.

throw -out spiral. A blank spiral groove cut in aneccentric manner at the end of a recording;provided to actuate the mechanism of an auto-matic record changer.

thump. A telegraph key click.

thyratron. A grid -controlled gaseous tube.tickler. A coil connected in the plate or grid cir-

cuit for the purpose of feeding a portion ofthe amplified signal current back into thegrid circuit by induction for repeated ampli-fication.

tiedown point. A frequency at which a receiver isaligned. Also, sometimes a tie point.

tie point. An insulated terminal used for con-necting a number of parts together.

tier array. An arrangement of antennas one abovethe other, used chiefly in ultra -high frequencywork.

tight coupling. The closest possible coupling between two circuits under given conditions.

tilting. An up or down movement of a televisioncamera.

time constant. In a capacitive -resistive circuit, thenumber of seconds required for the capacityto receive 63% of its full charge after the emfis applied. The time constant is equal to theproduct of the circuit's capacity in farads andits resistance in ohms. In an inductive -resistivecircuit, the number of seconds required forthe current to reach 63% of its final value afterthe emf is applied. The time constant is equalto the circuit's inductance in henrys dividedby its resistance in ohms.

time delay. The time that elapses between thetime an action should occur and the time atwhich it actually does occur,

time -delay circuit. A circuit that delays the trans-mission of a pulse, a signal, or a portion ofa signal for a definite desired period of time.

time -delay relay. A relay whose contacts openor close a specified length of time after thecontrolling pulse has been applied.

time gate. A transducer that gives output onlyduring chosen time intervals.

time multiplex. Successive transmission of pulsesamples of each of several signals.

time switch. A time -controlled switch. A timer.timing axis oscillator. An oscillator circuit that

generates a sawtooth voltage for the hori-zontal deflecting plates or horizontal deflectingcoils of a cathode-ray tube.

tinned wire. Copper wire that has been coatedwith a layer of tin or solder to simplify sol-dering.

tinsel cord. A highly flexible insulated cord inwhich the conductor is composed of strips ofthin metal foil, or tinsel, wound around astrong but flexible central Insulating cord.

tip. The contact at the end of a telephone -typeplug. Also the soldering surfaces of a solderingiron.

tip lack. A small receptacle into which a metalplug can be inserted to complete a circuit.

tip plug. A small plug that fits into a tip jack.TM waves. Transverse magnetic waves. Electro-

magnetic waves in a wave guide, when themagnetic field is transverse, and the electricfield waves are in the direction of propaga-tion.

T -network. A network composed of three im-pedance branches connected two in series withone side of a line, the third across the linebetween the other two.

toggle switch. A small switch operated by meansof a lever that is joined to the contact arm ina knee joint in such a way that the contactfingers move in the same direction as the forceactuating the lever.

tolerance. The permissible variation from a ratedor assigned value.

tone. The general character of a reproducedsound as it affects the human ear; the qualityof sound. Also, a single -frequency audio sound.

tone arm. In a record player, phonograph, orchanger, the arm that contains the cartridgeand stylus.

tone control. A circuit control sometimes pro-vided on a receiver to permit strengtheningthe response either at low or at high audiofrequencies at will.

tone generator. An audio -frequency signal gen-erator.

tone -modulated wave. An interrupted continuouswave, which is a continuous wave modulatedat an audio frequency.

tone modulation. Modulation of a carrier with afixed audio -frequency tone.

top cap. A metal cap sometimes placed on thetop of a vacuum tube and connected to one ofthe electrodes.

top -loaded antenna. A vertical antenna having thetop structure enlarged to increase the appar-ent length.

toroid. Ring -shaped. A doughnut -shaped coil.torque. The force that produces rotation.tower. A tall metal structure used to support an

antenna, or which itself is an antenna.T -pad. A resistive T -network used for providing'

attenuation and/or impedance matching.tracer. A thread of contrasting color in wire

insulation that aids in identification and trac-ing of the wire during maintenance and servic-ing of the equipment.

tracking. A term used to indicate how the tunedcircuits in a receiver follow the frequencyindicated by the tuning dial pointer as thereceiver is tuned over its entire tuning range.

transceiver. A radio device used for both trans-mitting and receiving.

transconductance. The effect on one electrode cur-rent of an ac voltage on another electrode.Mutual conductance. The most important is thecontrol -grid to plate transconductance, meas-ured by the ac grid voltage producing it.

transcription. An electrical recording.transducer. A device that transfers energy from

one system to another.transfer relay. A relay controlled by and con-

trolling other relays.84

transformer. Two or more coils mounted on acommon support in such a way that the mag-netic lines of force produced by the flow ofalternating or pulsating direct current throughone coil will pass through the other coil andinduce in it a corresponding ac voltage.

transformer -coupled amplifier. An amplifier usingtransformers for coupling.

transformer oil. An oil in which windings of largepower transformers are immersed for coolingand insulation, and to prevent oxidation,

transient oscillation. A momentary oscillationoccurring in a circuit during switching, or ata sharp change in the signal.

transient response. The manner in which an elec-trical circuit responds to sudden changes inapplied potential.

transients. Erratic changes in voltage or current.Also, a momentary voltage or current surge.

transient time. The time necessary for an elec-trical circuit to reach a normal operating con-dition after being turned on.

transistor. A unit consisting of a semi -conductingmaterial having a point contact with one ormore wires, used in place of tubes in someapplications involving rectification, detection.amplification, or oscillation. No filament orheater voltage is required.

transit angle. The product of angular frequencyand transit time.

transit time. The time taken by an electron topass through some specific area,

transition frequency. The frequency at which thechangeover from constant -amplitude recordingto constant -velocity recording takes place.

transitron oscillator. A negative -resistance oscil-lator similar to a dynatron, in which the innergrid is used as an anode, the outer grid as acontrol element, and the plate as a collectoranode.

translucent. Permitting the passage of light, butso scattering the rays that objects cannot beclearly seen.

transmission. Transfer of electric energy fromone location to another through conductors orby radiation or induction fields.

transmission level. The ratio of the power at agiven point in a transmission system to thepower at some point in the system chosen asa reference point.

transmission line. Any set of conductors used tocarry rf or of signals or' energy from one loca-tion to another.

transmission loss. The loss of power suffered bya transmitted wave in passing along a trans-mission path or through a circuit or otherdevice.

transmission unit. The decibel.

transmitter. A comprehensive term applying toall of the equipment used for generating, am-plifying, and radiating an intelligence signalinto space.

transparent. Permitting the passage of light rayswithout scattering.

transpose. To interchange position.

transposition. Interchanging the relative positionsof wires to neutralize the effects of inductionto or from other circuits. In two -wire parallellead-ins for an antenna, to minimize radia-tion from the lead-in during transmission, orto minimize interference pickup by the lead-in during reception.

transverse

transverse

transversement istion.

electric waves. See TE waves.

magnetic waves. See TM waves.

wave. A wave in which the displace -crosswise to the direction of propaga-

trapezoidal. Having the form of a trapezoid, aplane four-sided figure with two of the sidesparallel.

traveling -wave tube. A vacuum tube in which thesignal is caused to follow a wire helix. An elec-tron stream directed down the center of thehelix interacts with the electric field of thesignal to cause bunching, which in turn am-plifies the signal.

treble. The higher audio frequencies. The higheraudible tones.

triangulation. A method of fixing the position ofan aircraft or surface vessel by taking bear-ings with a radiocompass on at least two fixedland stations.

trickle charge. The continuous charging of astorage battery at a low rate, approximatelyequal to the rate of internal loss, to maintainit in a fully charged condition.

trickle charger. A device, usually a rectifier op-erating from an ac power line, designed to

. charge a battery continuously at a low rate.

trigger circuit. A multivibrator circuit in whicheither of the two tubes can operate stably, butthe triggering of either tube cuts off the cur-rent of the other. The flip-flop action is pro-duced by a trigger pulse in the grid of eithertube.

triggering. Starting action in a circuit, whichthen continues to function for a predeterminedtime under its own control.

trigonometric function. The ratios that exist be-tween the various sides and angles of a righttriangle.

trigonometry. A branch of mathematics that dealswith the relations existing among the anglesand sides of triangles.

trimmer condenser. A small semi -adjustable con-denser used in the tuning circuits of radioreceivers and other radio apparatus to permitaccurate alignment.

triode. A three -electrode vacuum tube.triode -pentode. A vacuum tube having a triode

and a pentode in the same envelope.

tripping device. Any mechanical or electromag-netic device used to open a circuit breaker orstarter, either when certain abnormal elec-trical conditions occur or when actuated man-ually.

tri-tet oscillator. A crystal oscillator using elec-tron coupling to the output circuit, popularwith amateur radio operators because it hasstrong harmonics that make it ideal for multi -band operation.

troposphere. That part of the earth's atmosphereextending outward from the earth for aboutsix miles, in which temperature generally de-creases with altitude, clouds form, and con-vection is active,

tropospheric wave. A radio wave reflected bysome part of the troposphere.

trough. In a modulated wave, the regions ofminimum output. In the atmosphere, the spacebetween two ionized reflecting layers,

TR switch. Transmit -receive device to preventapplication of full transmitter power to re-ceiver input.

85

true power. The power measured by a wattmeter,taking phase into consideration. In a reactivecircuit it is the product of voltage times cur-rent times a power factor.

trunnion. One of two opposite projecting pivots,such as those used to support a phono pickuparm.

tube. An electronic device in which conductionby electrons takes place through a vacuum ora gaseous medium within an air -tight glass ormetal envelope.

Courtesy Sylvania

Tubes

tube heating time. The time required for a tubeto reach normal operating temperature.

tube noise. Noise originating within a vacuumtube, such as microphonics and shot -effects.

tube tester. An instrument used to test the con-dition of radio tubes.

tube voltage drop. In a tube, the plate -cathodevoltage during the conducting period.

tubular condenser. A paper or electrolytic con-denser having as its plates long strips of foilrolled into a compact tubular shape.

tuned antenna. An antenna made to resonate atthe desired operating frequency.

tuned circuit. A resonant circuit, consisting ofa coil and condenser that are preset or canbe adjusted to give resonance at a desired.frequency.

tuned filter. A resonant circuit used to attenuatesignals at the resonant frequency.

tuned -grid oscillator. An oscillator whose fre-quency is determined by a parallel -tuned tankIn the grid circuit to which the plate circuitis coupled to provide the required feedback.

tuned -grid, tuned -plate oscillator. A vacuum -tubeoscillator having a parallel resonant circuit inseries with the plate circuit and anotherparallel resonant circuit in series with the gridcircuit. The grid resonant circuit is tuned tothe operating frequency, and the plate reso-nant circuit is tuned slightly above the oper-ating frequency, so as to act like an induct-ance. Oscillation is maintained by capacityfeedback through the internal capacity of thetube.

tuned -plate oscillator. An oscillator whose fre-quency is determined by a parallel -tuned tankin the plate circuit to which the grid circuitis coupled to provide the required feedback.

tuned radio -frequency amplifier. An rf voltage am-plifier circuit using tuned circuits in the cou-pling system.

tuned radio -frequency receiver. A receiver in whichrf amplification Is provided by a number ofvacuum tube amplifier stages, each of whichhas one or more circuits that are tuned to

resonance at the incoming signal frequency bya section of the gang tuning condenser.

tuned radio -frequency stage. A stage of amplifl-' cation, usually consisting of a vacuum tube

and one or more tuned circuits that can beresonated to the received signal.

tuned radio -frequency transformer. A transformerhaving one or both windings tuned; used forcoupling two rf amplifier stages.

tuned -reed frequency meter. See Frahm frequencymeter.

tuner. A device capable of selecting the desiredsignal, and delivering rf, i-f, or demodulatedinformation to some other equipment. Also,the portion of a receiver that contains circuitstuned to resonance at the received signal fre-quency and those tuned to the local oscillatorfrequency.

tungar bulb. A phanotron (hot -cathode, gas -discharge rectifier tube) having a heated fila-ment serving as cathode and a graphite discserving as anode in an argon -filled glass en-velope, used mostly in battery chargers.

tungsten. A metal used for the filaments andother elements of radio tubes.tuning. The process of varying the inductance or

'capacity in a coil -condenser circuit to pro-vide resonance at a desired frequency. Also,the process of setting all of the tuning circuitsin a radio receiver simultaneously to a desiredfrequency by rotating the tuning dial or press-ing a button of a push-button tuner.

tuning circuit. A circuit containing inductanceand capacity or an R -C network, which canbe adjusted so the circuit will be responsiveto a particular frequency.

control. The receiver control by which theoperator varies the tuned circuits of the re-ceiver to bring in the desired sound or tele-vision program.

tuning eye. See electron ray tuning indicator.tuning indicator. A device that indicates when a

radio receiver Is tuned accurately to a radiostation.

tuning meter. A meter connected into a radioreceiver circuit for use as a tuning indicator.

tuning wand. A flexible rubber or fiber rod hav-ing a brass plug in one end and a powdered-iron core at the other end, used for checkingreceiver alignment.

turn. In a coil, one complete loop of wire aroundthe coil form.

turnover. When measuring ac, the difference inmeter readings found when the leads of a vtvmare reversed, caused by unequal capacitiesbetween the vtvm circuits and ground.

turns -per -volt. The number of turns needed onthe secondary winding of a transformer to give1 volt of output voltage for a specified primaryvoltage.

turns ratio. The ratio of the number of turns ina secondary winding of a transformer to thenumber of turns in the primary winding.

turnstile antenna. A series of crossed horizontaldoublet antennas, arranged vertically on amast and fed 90° out of phase. Used wherecircular radiation patterns are desired.

turntable. In a record player or electric phono-graph, the motor -driven disc on which thephonograph record is placed. In a sound re-corder, the motor -driven disc on which isplaced the disc to be cut.

86

turret. A revolving plate sometimes mounted atthe front of a television camera and carryingtwo or more lenses of different types, used topermit rapid interchange of lenses. Also, arotatable device on which one or more pre -tuned circuits are mounted for use in receiv-ers, transmitters, and signal generators. Ro-tating the device connects a different pre -tuned circuit into the circuit and disconnectsthe others.

tweeter. A loudspeaker designed to handle onlyhigh audio frequencies (about 2000 to 15,000cycles).

twin lead. A transmission line consisting of twoparallel wires, molded into and held apart byrubber or plastic insulation.

twin -triode. Two triode tubes in a single envelope.

twin wire. A cable composed of two parallel -laidinsulated conductors having a common cover-ing.

twisted pair. Two insulated conductors twistedtogether, without a common covering.

two -band receiver. A radio receiver having tworeception ranges.

two-way communication. Communication betweenstations each of which has both transmittingand receiving equipment.

two-way switch. A switch used for controllingelectrical or electronic equipment componentsor circuits from either of two positions.

Uultor. In a cathode-ray tube, the electrode or

combination of electrodes to which is appliedthe highest dc voltage for accelerating theelectrons prior to deflection.

ultra-audion oscillator. A variation of the Col-pitts oscillator circuit, in which the, two volt-age -dividing capacitances are the plate -to -cathode and the grid -to -cathode capacitancesof the tube.

ultra -high frequency (uhf). A frequency in theband between 300 mc and 3000 mc. See radiospectrum.

ultraviolet. A range of radiation frequencies be-yond the visible spectrum at the violet, orhigh -frequency end.

umbrella antenna. An antenna in which the wiresare guyed downward in all directions from acentral mast or tower to the ground, some-what like the ribs of an open umbrella.

uncharged. Without electrical charge. Having anormal number of electrons.

undamped oscillations. Oscillations of an electro-magnetic wave whose energy source constantlyrestores losses incurred by the load or result-ing from radiations.

undamped wave. A continuous wave.

undercutting. Cutting too shallow a groove orcutting with insufficient lateral movement ofthe stylus during sound recording.

underlap. The amount by which the effectiveheight of the scanning spot falls short of thenominal width of the scanning line in a fac-simile system.

underioad relay. A relay that operates when thecurrent in a circuit drops below a minimumvalue.

undermodulation. Incomplete modulation at atransmitter.

undistorted output. The output associated withan arbitrarily low level of distortion estab-lished for a particular test or operation.

unidirectional. In one direction only.

unidirectional antenna. An antenna designed toradiate with maximum strength or receivewith maximum sensitivity in a particular di-rection and with minimum radiation or recep-tion fn the opposite direction.

unidirectional loop. A loop that will pick up energy from one direction only.

unidirectional microphone. A microphone that hasmaximum sensitivity to sounds from a par-ticular direction and minimum sensitivity tothose from the opposite direction.

unidirectional pulses. Single -polarity pulses thatall rise in the same direction.

uniform line. A transmission line that has iden-tical electrical properties throughout itslength.

unilateral bearing. A bearing obtained with aradio direction finder having a unidirectionalresponse.

unilateral conductivity. Conductivity in only onedirection, as in a perfect rectifier.

unipotential cathode. A cathode to which heat issupplied by an independent heater element.so there is no potential difference along it asa result of heater current flow. An indirectlyheated cathode, or equipotential cathode.

unit. A reference quantity for measuring pur-poses.

unit pole. A unit of measurement of magneticstrength. A unit pole repels a similar polewith a force of one dyne at a distance of onecentimeter.

unity coupling. The condition In which all themagnetic flux of the primary passes throughthe entire secondary.

unity power factor. A power factor of 1.0 ob-tained when current and voltage are in phase,as in a circuit containing only resistance orin a reactive circuit at resonance.

universal motor. A series -wound motor that maybe operated at approximately the same speedand output on either direct current or single-phase alternating current.

universal output transformer. An iron -core audiooutput transformer having a number of tapson its windings to permit matching to a widerange of load impedances.

universal receiver. A receiver capable of operat-ing from either ac or de power.

unloaded Q. The Q of a system when there is noexternal coupling to it.

unmodulated. Without modulation. The carriersignal alone, as it exists during pauses be-tween programs.

unmodulated groove. A silent groove on a record-ing; a groove cut without sound.

untuned. Not resonant at any of the frequenciesbeing used.

Vvacuum. A space from which practically all air

or gas has been removed.vacuum tube. A tube evacuated to such a degree

that its electrical characteristics are essen-87

tially unaffected by the presence of residualgas or vapor.

vacuum -tube keying. A telegraph keying system inwhich a vacuum tube is placed in series withthe center -tap lead of the final stage, its gridbeing connected to its filament through thetransmitting key. When the key is open, thetube blocks and no plate current flows. Ground-ing the grid (closing the key) unblocks thetube, current flows, and a pulse is sent out.

vacuum -tube voltmeter (vtvm). A test instrumentthat utilizes a vacuum -tube circuit for measur-ing voltages without greatly affecting the cir-cuit to winch tne instrument is connected.

valve. British for radio tube.V antenna. See vee antenna.variable condenser. A condenser whose capacity

can be changed either by varying the spacebetween plates (as in a trimmer condenser)or by varying the amount of meshing betweenthe two sets of plates (as in a tuning con-denser).

variable coupling. Inductive coupling of two ormore coils that can be varied by moving oneor more in relation to the others.

variable -impedance tube. See reactance tube.variable inductance. A coil whose inductance can

be cnanged by varying the number of turnsin use, or by moving a core made of powderediron or brass.

variable -mu tube. A tube having a control gridso designed that the mutual conductance varieswith the C bias.

variable resistance. A resistance that can bechanged in value while in use.

Variac. A transformer whose output voltage canbe varied over a wide range by means of aswitch and a series of taps.

variocoupler. A variable rf transformer consistingof two independent windings. one stationaryand the other adjustable with relation to thefixed element so the mutual inductance can bechanged.

variometer. A variable inductance having a mov-able coil mounted inside a stationary one. Thetwo coils are connected in series. The totalinductance of the unit can be varied continu-ously through a wide range of values by ro-tating the inner coil.

Varley bridge. A variation of the Wheatstoneresistance bridge, used to determine distancefrom the bridge to the point at which a lineis grounded.

vector. A straight line whose length is propor-tional to the magnitude or amount of a quan-tity, and whose arrow head points in the di-rection of motion or force of that quantity.

vector diagram. An arrangement of vectors show-ing the relations between alternating quanti-ties.

vector quantity. A quantity that has both magni-tude and direction.

vee antenna. A single -wire antenna arranged inthe form of a "V." Also, an antenna consistingof four rods arranged to form two V's, lyingin the same plane, with apexes pointing inthe same direction, and with the correspond-ing sides connected in parallel.

velocity microphone. A microphone made up of athin, light -weight corrugated ribbon mountedbetween the poles of powerful permanent mag-nets. Sound waves move this conducting rib-bon back and forth in the magnetic field, andan of voltage is induced in the ribbon. The

ribbon responds to the velocity of the airparticles rather than to air pressure.

velocity -modulated oscillator. A vacuum -tubestructure in which the velocity of an electronstream is varied in passing through a resonantcavity, called a buncher. Energy is extractedfrom the bunched electron stream as it passesthrough a second cavity resonator, called thecatcher. Oscillations are sustained by cou-pling energy from the catcher cavity back tothe buncher cavity.

velocity modulation. A system of varying thevelocity of electrons in a stream so they bunchto form a modulated wave. Also, a televisionsystem in which the picture -tube beam currentIs maintained constant and the change inbrightness of the reproduced picture isachieved by varying the horizontal velocity ofthe spot in both the picture and camera tubein accordance with the brightness of the pic-ture on the mosaic of the camera tube.

vernier. An auxiliary device used with a maindevice to obtain fine adjustment.

vernier condenser. A small variable tuning con-denser placed in parallel with a larger tuningcondenser for the purpose of providing a fineradjustment after the large condenser has beenset roughly to the desired position.

vernier dial. A dial in which a large rotation ofthe control knob makes the controlled shaftrotate only a small fraction of a revolution,permitting fine and accurate adjustment.

vertical amplitude control. See height control.vertical antenna. A single vertical metal rod,

suspended wire, or metal tower used as anantenna.

vertical blanking pulse. In television, a pulse trans-mitted at the end of each field to cut off thecathode-ray beam while it is returning to startthe next field.

vertical centering control. A control provided ina television receiver or cathode-ray oscillo-scope to shift the position of the entire imagevertically on the screen.

vertical deflecting electrodes. The electrodes of anelectrostatic cathode-ray tube to which voltageis applied to move the electron beam up anddown (from top to bottom) on the screen.

vertical hold control. The control in a televisionreceiver that adjusts the free -running periodof the vertical sweep oscillator.

vertical linearity control. In television, a controlprovided for adjustment of the uniformity ofdistribution of picture elements in a verticaldirection.

vertical oscillator. The sawtooth scanning gen-erator that furnishes the required voltage orcurrent wave for vertical scanning.

vertically polarized wave. An electromagneticwave in which the electric field is perpen-dicular to the earth.

vertical positioning control. See vertical centeringcontrol.

vertical radiator. A conductor or system of con-ductors perpendicular to the earth, used as anantenna for transmitting or receiving.

vertical recording. A recording in which thegroove modulation is up and down. Also calledhill and dale recording.

vertical resolution. The definition or clarity of atelevision image in the vertical direction.

vertical retrace. The return path of the electronbeam across the raster from bottom to top atthe end of each field.

88

vertical scanning. The movement of the beam onthe picture tube in the vertical direction.

vertical -scanning generator. See vertical oscillator.

vertical speed control. See vertical hold control.vertical sweep. The downward movement of the

electron beam, line by line, from the top tothe bottom of a picture or scene being tele-vised.

vertical synchronization. Making the verticalscanning at the receiver occur at the same rela-tive time as the vertical scanning at thecamera. .

vertical synchronizing pulses. A series of pulses,longer in time duration than the horizontalpulses, that occur between each field and thatare used to synchronize the vertical scanningoscillator.

very high frequency (vhf). A frequency in theband between 30 mc and 300 mc. See radiospectrum.

vestigial sideband. The transmitted portion ofthe suppressed sideband.

vestigial sideband transmission. The system ofmodulation in which the carrier is modulatedby a complete sideband and a vestige or partof the other sideband.

vibrate. To move back and forth.vibrating -reed frequency meter. See Frahm, fre-

quency meter.vibrator. An electromagnetic device that con-

verts a de voltage to pulsating dc or ac.

Courtesy P. It. Mallory and Co.

Vibrator

video. A Latin word meaning "I see," applied totelevision parts and circuits that handle pic-ture signals, and to signals associated withthe picture being transmitted.

video amplifier. See video -frequency amplifier.

video frequency. The frequency of the signalvoltage containing the picture information re-sulting from the television scanning process.

video -frequency amplifier. The amplifier stagesafter the video demodulator stage that buildup video signal strength. Also any wide -bandamplifier.

video signal. The picture signal in a televisionsystem.

view finder. An attachment on a television camerato enable the cameraman to observe the areacovered by the camera.

viewing screen. In a cathode-ray oscilloscope orpicture tube, the screen that converts theuseful energy of, the electron beam into avisible pattern.

vinculum. A straight horizontal line serving asa sign of grouping, used chiefly with radicalsigns and fractions. Examples: VR2 + X2,

ab . When used with fractions, the yin -a + bculum indicates that the entire group abovethe line is to be divided by the entire groupbelow the line.

virtual cathode. The space charge or electroncloud in front of the cathode in a vacuum tube.

visible radiation. Radiation corresponding to thevisible spectrum of light. Roughly 4000 to7000 angstrom units.

vitreous. Having the nature of glass.vitreous enamel. A hard, glass -like enamel, used

as an insulation on large wire -wound resistors.voder. (Coined from Voice Operation DEmon-

stratolt.) A device consisting of vacuum tubecircuits and highly selective electrical filterscontrollable through a keyboard in such a waythat speech sounds can be artificially produced.

voice coil. A moving coil attached to the dia-phragm of a dynamic loudspeaker, to whichaudio voltages are applied.

voice frequency. The essential frequency rangeof ordinary speech, from about 100 to 3000cycles.

volt. The pratical unit of voltage or electro-motive force. One volt will send a current ofone ampere through a resistance of one ohm.

voltage. The force causing motion of electrons,measured in volts. Electromotive force.

voltage amplification. Amplification that increasesthe voltage of a signal rather than its power.Also, a rating obtained by dividing the acoutput voltage of an amplifier stage by theac input voltage.

voltage amplifier. An amplifier designed primarilyto build up voltage without supplying anyappreciable amount of power.

voltage difference. See potential difference.voltage divider. A resistor having one or more

fixed or adjustable contacts along the lengthof its resistance element, in addition to thecustomary two end terminals. The total avail-able voltage is applied between the two endterminals, and desired portions of this volt-age are obtained from any two terminals onthe voltage divider. Also, two or more resistorsconnected in series to serve the same purpose.

voltage doubler. A rectifier circuit that doublesthe output voltage by charging a condenseron one half -cycle and discharging it in serieswith the applied voltage during the next half -cycle.

voltage drop. The voltage developed across theterminals of a radio part by the flow of cur-rent through the part.

voltage feed. A method of exciting a transmittingantenna by applying voltage at a voltage loopor antjnode.

voltage feedback. A form of degeneration in whichthe feedback is proportional to the outputvoltage.

voltage gain. Voltage amplification. A rating -ofan amplifier stage obtained by dividing the acoutput voltage by the ac input voltage.

voltage multiplier. A precision resistor used In89

series with a voltmeter to extend its measuringrange.

voltage node. Any point that has zero voltage.voltage regulation. The ability of a generator

or other voltage source to maintain nearlyconstant terminal voltage for all load valuesfrom zero to the maximum rated capacity.

voltage -regulator tube. A two -element gaseoustube used to maintain a constant dc potentialacross a circuit. Also, a resistor in a glass ormetal envelope used in ac radio receivers tokeep the input ac voltage to the receiver powerpack essentially constant despite wide varia-tions in the line voltage.

voltage relay. A relay that functions at a chosenvalue of voltage.

voltage rise. A generated or source voltage.voltage saturation. The plate voltage at which

all electrons emitted from the cathode are be-ing collected by the plate so that further in-creases in plate voltage have no effect on platecurrent. Also known as plate saturation.

voltaic cell. Any cell that produces voltage.volt-ampere. The unit of apparent power in an ac

circuit containing reactance. It is equal to thevoltage in volts multiplied by the current inamperes, without regard for phase.

voltmeter. A meter used to measure electricalpressure or voltage in volts.

volt-ohm-milliammeter. See multimeter.

volume. The intensity or loudness of sound.volume compression. Limitation of volume range

so overmodulation will not take place.volume control. A device that varies the af out-

put of a receiver or public address amplifier,thereby changing the volume of the soundproduced by the loudspeaker.

volume expander. A manually adjusted audio cir-cuit that can be set to increase the volumerange of a radio program or phonograph recordby making the loud portions of the programlouder, thereby counteracting volume compres-sion at the transmitter.

volume indicator. A meter that indicates the vol-ume level of sound.

volume -limiting amplifier. An amplifier containingan automatic device that functions when theinput volume exceeds a predetermined level toreduce the gain so that the output volume isthereafter maintained substantially constantnotwithstanding further increase in the inputvolume. The normal gain of the amplifier isrestored when the input volume returns belowthe limiting level.

volume unit (vu). A unit specifying the number ofdb above a reference level of 1 mill iwatt (.001watt). When a level is given in volume units,there is no need to specify the referencelevel since it is implied in the definition ofvu. A vu is equal to a db when changes inpower are involved.

volume -unit indicator. An instrument calibrated toread af power level in vu's when connectedacross a 600 -ohm line.

wwafer socket. A socket in which the clips for

gripping the tube prongs are mounted betweentwo wafers or plates of insulating material.

wafer switch. A switch whose fixed contacts are

mounted in a circle on one or more plates ofinsulating material.

walkie-talkie. A small portable transmitter -re-ceiver.

water-cooled tube. A transmitting tube whoseplate element is cooled by circulating water.

watt. The practical unit of electrical power. Ina de circuit, the power in watts consumed bya device is equal to the applied voltage multi-plied by the current in amperes. In an ac cir-cuit, however, the power value obtained inthis manner must also be multiplied by thepower factor of the device.

wattage rating. A rating expressing the maximumpower a device can safely absorb or handle.

watt-hour. Unit of electrical energy. One wattexpended for one hour equals one watt-hour.

watt-hour meter. A meter that measures andregisters electric energy in watt-hours or kilo-watt-hours.

wattmeter. A meter used to measure the power inwatts or kilowatts that is being consumed bya device.

watt -second. One watt acting for one second,equal to one joule.

wave. A propagated disturbance or vibration ina medium, usually periodic, as an electricwave or sound wave; a single cycle of such adisturbance.

wave angle. The angle at which a radio waveleaves a transmitting antenna or arrives at areceiving antenna. The two angles needed tospecify the direction of a radio wave are theazimuth angle (corresponding to a directionabove the surface of the earth) and the devia-tion angle with respect to the surface of theearth.

wave antenna. An antenna approximately onewave -length long at the operating frequency.

wave band. A band of frequencies, such as thatassigned to a particular type of communica-tion service. Waves between two arbitrarilychosen wavelengths, including waves of alllengths between the lowest and highest chosen.

wave -band switch. A switch used in a transmitteror receiver to change from one wave band toanother.

wave duct. A tubular conductor capable of con-centrating the propagation of radio waveswithin its boundaries.

waveform. The shape of a wave as shown pic-torially or graphically, usually with referenceto changes in voltage or current. Also waveshape.

wave front. A plane parallel to the magnetic andelectrical lines of force.

wave guide. A tubular conductor through whichultra -high -frequency electromagnetic wavesare directed. More generally, any system ofmaterial boundaries capable of guiding radiowaves.

Wave Guide Section

90

wavelength. The distance traveled in a time ofone cycle by an alternating current, soundwave, or radio wave. This is the same as thedistance between successive peaks having thesame polarity in the wave.

wavemeter. A device arranged and calibrated tomeasure or indicate the length of a radiatedwave directly in meters, or its frequency.

wave trap. A device sometimes connected to theaerial system of a receiver to reduce thestrength of signals at a particular frequency.

wave velocity. The velocity of propagation ofenergy.

wave winding. A type of winding of an armaturein which each coil is connected to segmentson opposite sides of the commutator.

wax. The heavy blank wax disc used in makingthe master record required for the productionof phonograph records.

weak coupling. Loose coupling.

wedge. The convergent, fan -shaped pattern ofequidistant black and white tapering lines ona television test pattern.

weighting. The artificial adjustment of measure-ments in order to account for factors whichin the normal use of the device would other-wise be different from the conditions duringmeasurement.

wet cell. A cell in which the electrolyte is inliquid form.

wet electrolytic condenser. An electrolytic con-denser that uses a liquid electrolyte.

Wheatstone bridge. An instrument invented bySir Charles Wheatstone, English physicist, andused for accurate resistance, inductance, orcapacity measurements. The balance betweenthe known and unknown values is indicated bythe absence of current in a wire that forms abridge or path between opposite junctions ofthe circuit.

wheel static. Intereference in auto radios causedby friction between the tires and the pave-ment.

white. The signal produced at any point in afacsimile system by the scanning of a selectedarea of subject copy having minimum density.Also the brightest portion of a televisionimage.

wide-angle lens. A lens having a short focallength, so as to give a wide field of view.

width. In television the horizontal dimension ofthe picture. Also, the time duration of a pulse(pulse width).

width control. The control on a television receiverwhereby the horizontal dimension of the pic-ture is adjusted to fill the picture tube.

Wien bridge. A bridge circuit in which capacitycan be measured in terms of resistance andfrequency; also useful for measuring fre-quency and for finding power factor of con-densers.

wind charger. A generator driven by a wind -activated propeller mounted on or geared to itsshaft.

winding. One or more turns of wire that make upa continuous coil.

window end. End of a TV camera tube throughwhich the image is directed to the mosaic.

wire. A metallic conductor having essentiallyuniform thickness, used in radio chiefly toprovide a path for electric currents between

two points. Also, the act of making connec-tions.

wired radio. Communication by means of a modu-lated rf carrier signal traveling through wiresinstead of through space.

wire gauge. A system of numbers used to desig-nate wire sizes (diameters). The AmericanWire Gauge or AWG (formerly Brown andSharpe or B. & S. Gauge) is in common usein this country, and has numbers rangingfrom 0000 as the largest size to 40 and beyondfor the smallest sizes.

wireless. Radio.

wireless record player. A motor -driven turntableand phono pickup mounted in the same cabinetwith an rf oscillator. The phono pickup con-verts a recording into of signals that modu-late the rf carrier of the oscillator. The result-ing signal is radiated through space as aminiature broadcast signal, and can be pickedup by any radio receiver in the same housemerely by tuning that receiver to the broad-cast -band frequency on which the wirelessrecord player is operating.

wirephoto. A process of transmitting facsimilesof pictures over telephone wires by convertingthem into and reconverting them frofn elec-trical signals.

wawa

Wire -wound Resistor

wire -wound resistor. A resistor constructed bywinding a resistance wire on an insulatingform.

wobbulator. A device used with a signal generatorto vary the frequency between two valuesperiodically.

womp. A sudden flare-up of brightness in a tele-vision picture.

woof. A word -sound used by engineers to checkpeaks.

woofer. A loudspeaker designed particularly forthe reproduction of low audio frequencies atfairly high power levels.

work. The product of the force acting on a bodyand the distance through which the body ismoved.

working voltage. The highest voltage that can beapplied continuously to a condenser withoutcausing a breakdown of the dielectric.

wow. A flutter of low frequency, perceptible tothe ear as a change in pitch during reproduc-tion of a recording, caused by small variationsin the speed of the turntable.

X axis. A reference axis in a quartz crystal. Also,the horizontal axis of a graph, or the hori-zontal sweep path in a cathode-ray oscillo-scope.

X -cut. A piezoelectric crystal or quartz plate cutin such a manner that the X axis is perpen-dicular to its faces. Sometimes called a Curiecut.

91

x-rays. Rays having frequencies between thehigher ultra -violet frequencies and the lowergamma rays. They are produced by the strik-ing of cathode rays on a solid and are capableof penetrating opaque objects.

xtal. Abbreviation for quartz crystal.

YYogi array. An arrangement of dipole antenna

elements for television reception in whichone element acts as the antenna and the othersas parasitic elements (directors and/or a re-flector) to improve gain and directional re-ception pattern.

Y-axis. In a quartz crystal, a line perpendicularto the two diametrically opposite parallel faces.It lies in a plane at right angles to the X axis.Also, the vertical axis of a graph, or the ver-tical sweep path in a cathode-ray oscilloscope.

Y -cut. A piezoelectric crystal cut in such a man-ner that the Y-axis is perpendicular to itsfaces. Also sometimes called a face -parallelcut or 30° cut.

Y network. A circuit of three resistors or im-pedances arranged in the form of a Y or star.

yoke. See deflection yoke.

Z axis. The optical axis of a crystal, perpen-dicular to the X and Y axes.

Z-axis modulation. In a cathode-ray oscilloscope,the varying of the number of electrons in thebeam so as to change the intensity or bright-ness of the spot on the screen.

Zeppelin antenna. An antenna one-half wave-length long or a multiple thereof, fed at oneend by one lead of a transmission line.

zero -beat. A condition where no beat frequencyresults from combining two frequencies, be-cause the two frequencies are exactly thesame.

zero bias. Zero de voltage between the controlgrid and the cathode of a vacuum tube, so thatthese two electrodes are at the same de poten-tial.

zero level. The reference level used when specify-ing a level in decibels.

Z marker. A radio beacon station installed at aradio range station to mark the exact locationof the range station.

zone of silence. An area in which radio signalscannot be received.

93

Abbreviations of Radio Terms

Aa. Ampere.A. Filament circuit or filament voltage supply.

Antenna, ammeter, ampere, or area.A-. Symbol for the negative terminal of an A

battery or other filament -voltage source.A+. Symbol for the positive terminal of an A

battery or other filament -voltage source.abc. Automatic bass compensation.ac. Alternating current.adf. Automatic direction finder.af. Audio frequency.afc. Automatic frequency control.agc. Automatic gain control.Al. Aircraft interception.AIEE. American Institute of Electrical Engineers.

AM. Amplitude modulation.

amp. Ampere.

ant. Antenna.antilog. Antilogarithm.ARRL. American Radio Relay League.ATC. Air traffic control.avc. Automatic volume control.ave. Automatic volume expansion.AWG. American wire gauge.

B

B. Plate circuit or plate voltage supply. Alsomagnetic flux density.

B-. Symbol for the negative terminal of the Bbattery or other plate voltage source.

B+. Symbol for the positive terminal of a Bbattery or other plate voltage source.

back emf. Back electromotive force.BBC. British Broadcasting Corporation.bc. Broadcast.BCI. Broadcast interference.BC6. Amateur radio abbreviation for broadcast

listener.bfo. Beat frequency oscillator.B. & S. Brown & Sharpe (wire gauge), now

known as American Wire Gauge (AWG).btu. British thermal unit.

CC. Grid circuit or grid voltage supply. Capacity,

condenser, center tap, or Centigrade.C-. Symbol for the negative terminal of a C

battery or other grid voltage source.

C+. Symbol for the positive terminal of a Cbattery or other grid voltage source.

°C. Degrees Centigrade.

CAA. Civil Aeronautics Administration.CBS. Columbia Broadcasting System.cc. Cubic centimeter.cgs. Centimeter -gram -second.

CH. Choke coil.

cm. Centimeter.

coax. Coaxial.

CODAN. Carrier operated device, anti -noise.CONS. Carrier -operated noise suppression.cos. Cosine.

cot. Cotangent.cp. Candlepower.

cps. Cycles per second.cro. Cathode-ray oscilloscope.

csc. Cosecant.

cw. Continuous waves.

D

d. Distance. Diameter.db. Decibel.dc. Direct current.dcc. Double cotton -covered insulation on wires.DET. Detector tube or stage.df. Direction finder.dpdt. Double -pole, double -throw.

dpst. Double -pole, single -throw.

dsc. Double silk -covered insulation on a wire.dt. Double -throw.

DX. A slang expression for distance.

E

E. Electromotive force or voltage.Eb. Plate supply voltage. Also battery voltage.Eg. Grid voltage of a tube.,tmf. Electromotive force.

emu. Electromagnetic unit.Ep. Plate voltage of a tube.Esg. Screen -grid voltage.

esu. Electrostatic unit.

f. Frequency.F. Filament.

F

93

°F. Degrees Fahrenheit.FCC. Federal Communications Commission.FM. Frequency modulation.ft. Feet.

that a particular value is to be multiplied by1000.

ma. Milliamperes.

MBS. Mutual Broadcasting System.mc. Megacycles.

G mcw. Modulated continuous waves.G. Grid of a tube. Generator. Conductance. meg. Megohm.GCA. Ground -controlled approach. mfd. Microfarads.GCI. Ground -controlled interception. mh. Millihenry. Sometimes microhenry.GE. General Electric Co. mho. The unit of conductance.Gm. Mutual conductance of a tube. min. Minutes. Minimum.GMT. Greenwich Mean Time. mm. Millimeter.gnd. Ground. mmf. Micromicrofarads.

H

h. Henrys.

H. Heater or filament of a tube. Magnetic intensity or magnetomotive force per cm.

hp. Horsepower.

I. Current.

icw. Interrupted continuous waves.i-f. Intermediate frequency.

IFF. Identification friend or foe.ILS. Instrument landing system.In. Inches.

ip. Plate current of a tube.IRE. Institute of Radio Engineers.

J

j. An imaginary number.

K

K. Cathode of a tube. Also used to indicate thatsome value is to be multiplied by 1000. Alsoused in formulas to represent a constant ornumerical value that does not change its valueduring any one discussion. P. Plate of a tube. Power in watts. Primary

kc. Kilocycles per second. winding of a transformer.

kw. Kilowatts. PA. Public address. Power amplifier.

MO. Master oscillator.MOD. Modulator. Modulation. Modulated.MOPA. Master oscillator power amplifier.MTI. Moving target indicator.my. Millivolts. Sometimes microvolts.my/m. Millivolts per meter. Sometimes micro-

volts per meter.mw. Milliwatts.

N

N. Number of turns on a coil.NBC. National Broadcasting Company.NC. No connection.NEMA. National Electric Manufacturers AssOcia-

tion.

Oorth. Orthicon.osc. Oscillator.oz. Ounces.

kwh. Kilowatt-hours. PAM. Pulse amplitude modulation.

kv. Kilovolts. PDM. Pulse duration modulation.

kva. Kilovolt -amperes. pf. Power factor.PFM. Pulse frequency modulation.PIM. Pulse interval modulation.

I. Length.PLM. Pulse length modulation.

L. A coil or inductance in henrys. PM. Permanent magnet. Phase modulation.lb. Pounds. PPI. Plan position indicator (radar).LC. Inductance times capacity. PPM. Pulse position modulation.

ts.4 PRI. Primary winding of a transformer.m. Meters. PTM. Pulse time modulation.M. Mutual inductance. Also, used to indicate PWM. Pulse width modulation.

94

Q TV. Television.

Q. The merit (degree of perfection) of a coil orcondenser.

R

R. Resistor; resistance in ohms.R -C. Resistor -condenser coupling.

RC. Product of resistance and capacitance.RCA. Radio Corporation of America.RDF. Radio Direction Finding.rf. Radio frequency.RFC. Radio -frequency choke coil.

RMA. Radio Manufacturers Association. NowRTMA.

RMCA. Radio Marine Corporation of AmericaRTMA. Radio and Television Manufacturers As-

sociation.

rms. Root mean square.Rp. Plate resistance of a tube.rpm. Revolutions per minute.

S

S. Secondary winding.scc. Single cotton -covered insulation.sce. Single cotton covering over enamel.sec. Secant. Seconds.SEC. Secondary winding of a transformer.SG. Screen grid.shf. Super high frequencies.sin. Sine.,

SOS. International marine distress signal.spdt. Single -pole, double -throw.

spst. Single -pole, single -throw.

sq ft. Square feet.sq in. Square inches.

ssc. Single silk -covered.

SUP. Suppressor grid of a tube.super. Superheterodyne.SW. Short-wave. Switch.

SWL. Short-wave listener.SWR. Standing -wave ratio.

T

fan. Tangent.TE. Transverse electric.TM. Transverse magnetic.TPTG. Tuned -plate, tuned -grid.

TR. Transmit -receive.

trf. Tuned radio frequency.TU. Transmission unit (replaced by db).

U

uhf. Ultra -high frequency.

V

V. Volts. Voltage. Voltmeter. Vacuum tube.vhf. Very high frequency.

VT. Vacuum tube.

vfvm. Vacuum tube voltmeter.vu. Volume unit.

wW. Power in watts.

X

X. Reactance.

Xc. Capacitive reactance.

Xr,. Inductive reactance.xfal. Crystal.

Y

Y. Admittance.

zZ. Impedance.

GREEK LETTERS USED IN RADIO

e (epsilon) 2.718, the base of the natural sys-tem of logarithms.

f (theta) Angles, especially, phase angle.X (lambda) Wavelength.

p (mu) Micro (one millionth of).Amplification factor.Permeability.

ma Microampere.

pf Microfarad.Microhenry.

Micromicro (one millionth of onemillionth of).

p.p.f Micromicrofarad.pard Micromicrofarad.

Microvolt.

pv/m Microvolts per meter.Microwatt.

w (pi) 3.1416, the ratio of the circumfer-ence of a circle to its diameter.

p (rho) Specific resistance.

w (omega) Ohm. Angular velocity (2rf).0 (omega) Ohm, sometimes megOhm.

95

COMMON RADIO SYMBOLSBC ANTENNA

...(15-0-0-\. AIR -CORECOIL OR CHOKE DIODE TUBE(6)

TV -FM ANTENNA -dingPERMEABILITY-TUNED COIL

TRIODE TUBE4LOOP ANTENNA

IRON -CORE

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