a dictionary of radio terms

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A ilI[TIONARYTR A I I O T R M SConcise Definitionsof commonlyused words in Radio, Electronics

and Television

Compiled una"lth" directionofthe TechnicalStafi ofAll ied Radio Corp.

*Edited by

L . O . G O R D E RConsull ing Radio Engineer

Professorof Radio EngineeringCHICAGO TECHNICALCOLLEGE

R E Y I S E D 9 4 4 E D I T I O N

PublishedyAI,I.IEIT ANIOCORPORATIONChicago,ll., U. S. A.

COPYRIEHT I9 , I4 BY ALL IED RADIO CORPORATION


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FOHEWINilThe necd of simpleexplanations [ commonlyused adio erms asexisted evel since here hasbeen generalpublic interest n radio.This need has especial lybeen made evident from thousandroffettershanciiedannually by the TechnicalStaffof the Allied RadioCorporation. Allied has, herefore,made this dictionary availableto speed the progress [ radio beginners, xperimentersnd stu-dents and to serveas a relerence o advanced adio men who seekto refresh heir memorieson precisemeanings [ the more echnicalradio terms.This booklet containssimple, ecsy-to-understand efinitions ofcpproximately800 radio erms nd abbreviations ost ikely to beencounteredn magazine rticles, ooksand lectures n radio anditsal l ied f ieldsof electronics,elevision nd acsimil ie roadcasting.Schematic ymbols, ips on reeding ircuitdiagrams,nstructionrfor using he R.M.A. Color Code, and other useful adio dataaregroupedat the end of the book.THE TANGUAGE F RADIO Radio, l ike any other special izedfield of endeavor, asa special anguage hich aci l i tates xplana-tionsand discussionsf its problems. his anguagencludeswords,abbreviations,etters,and schematic ymbols,each representingan idea or a picture.Radio terms ike plate, choke,spider, and jammingare ordinarywords o which radiomen haveassigned pecialmeanings. nly afew entirelynewwordswerecreated uring he rapiddevelopmentof radio, superheterodyne, entode,andmicrophoneare examples.

By reading his entiredictionary areful ly_iustnce,q lew pageseachday, anyonecan becomesurprisinglyamil iarwith the verbalportiono[ the language f radio.Thiswil l includealso he abbrevia-tions and letters ured lor convenience o represent ingle words.The schemctic ymbolswhich a radio man uses o show circuitconnectionsmight be called a system f radioshoilhand,or theseodd combinations f l ines,arrowsand curvesallow him to drawcompletediagrems f radio sets n a few minutes. he meanings fthesesymbolsare given near he end of this booklet. Once youlearn to recognize each one, you will oftentimes prefer thesesymbol diagramso more elaborate ictorialdiagrams.


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A DICTIONARYOF RADIO TERMSA

A-. (A negative or A minus') Symbol usedto designate he point in a circuit to whichthe negative terminal of the filament sup-plv is to be connected.A+. (A positive or A plus.) Symbol used todesignite the point -in a circuit to whichthe positive terminal of the filament supplyis to be connected.A battery. The battery (often a single drycel l) used or supplying heating current tothe filaments of radio tubes.AB power pack. A combination of batteriesor devices in a single housing, used to sup-ply operating potentials for receivers, es-pecially portable sets.a.c. Alternating current,acousti'c. Pertaining to sound.acoustic feedback. Transfer of sound wavesfrom a loudspeaker to any. previous part,such as a microphone, n the same ampli-fying or broadcasting system. It canciusE howling and ov-el loadingof tubes.a.c.-d.c. receiver. A receiver which will oper-ate either from an a.c. or d.c. power source.It does not have a power transformer.a.c. receiver. A receiver designed to operateonly from an a.c. power source. Powerpacks of these sets invariably employ apower transformer for stepping the a.c.line voltage ttp or down.adapter. Any device used for changing tem-porarily or permanently the terminal con-nections of a circuit or part.admittance. The measure of ease with whichan alternating current flows in d circuit.The reciprocal of impedance. Measuredin micromhos or mhos.aerial. An antenna.a.f. Audio frequency.a.f.c. Automatic frequency control.air-cell A battery. A non-rechargeable wet-cell batterylvhich usually is built to deliver2 volts, for use chiefly in battery-operatedhome radio receivers. Its carbon electrodesare porous and absorb oxygen from theair during use. Rated life in normal radiouse is 500 to 1500 hours, depending uponbattery size and current drain.

air-core. A term usd to describe coils ortransformers which have no iron in theirmagnetic circuits. Air-core construction isused chiefly in r.f. circuits.air gap. A path for electrical or magneticenergy through air between two objects,such as between the electrodes of a sparkgap or between core sections of an iron-core transformer.airplane dial. Popular name for a circular-shaped radio receiver dial with a rotatingpointer, resembling the dials and pointersof airplane instruments.aff i r\on-r4erdrrc wrgncn

Non Metall ic ScrewdriverTY?Es OF ATIGNING TOOLS

aligning tool. An essentially non-metallicscrewdriver or socket wrench used for ad-justing the trimmer condensersand adjust-able coils which are provided in radio

for making quick temporary'connections.all-metal type tube. A vacuum tube havinga metal envelope instead of a glass enve-lope. Electrode connections are madethrough glass beads fused into the top andbottom of the metal envelope. The octalbakelite base is designed to take eightequally spaced terminal prongs, but som,eof the prongs are omitted on tubes havingless than eight terminals.alloy- A mixture of two or more metals.all-wave antenna. A receiving antenna de-signed to pick up stations reasonably wellover a wide range of carrier frequenciesincluding short-wave bands as well as thebroadcast band. It may be a single doubletantenna or a combination of two or moredoublets.

3

F oFl-++ sofr.--.{ F--r fr .-J

TYPESOF ALL.WAYE ANTENNAS

F- rc rr. ----t* Jo r ----1


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all-wave receiver. A receiver capable of re-ceiving stations on all of the 'commonlyused wavelengths in short-wave bands aswell as the broadcast band.alternating current. An electric current whichreverses its direction of flow at regularintervals many times per second.a.m. Amplitude modulation. Also written asa-m or AM. See amplitude modulation.amateur. Any person who operates and ex-periments with short-wave transmittersas a hobby rather than for profit.amateur bands. Bands of fiectuencies as-signed exclusively to radio amateurs by theFedera l Communica t ions Commiss ion ,Amateur band limits are:1 , 7 1 5 t o 2 , 0 0 0 k c . 2 8 , 0 0 0 t o 3 0 . 0 0 0 k c .t ,500 to 4 ,000 kc . 56 ,000 to 30.000 kc.? , 0 0 0 t o ? , 3 0 0 k c . 1 1 2 , 0 0 0 t o 1 1 6 . 0 0 0 k c .1 4 , 0 0 0 t o 1 4 , 4 0 0 k c . 2 2 4 , 0 0 0 t o 2 3 0 , 0 0 0 k c .Amateurs may also operate on any frequencyabove 300,000 kc .amateur operator. A person holding a validl icense issued by the F.C.C. authorizing

him to operate licensed amateur stations,amateur station. A radio station used bv anamateur for personal communication withother amateurs,amateur station call letters. Identifying callsignal assigned to a licensedamateur oper-ator to identify his station. Amateur callsin a given country begin with a one ortwo-letter prefix (W or N for U.S., and Kfor U.S. possessions), ol lowed by a loca-tion-indicating numeral and two or moreadditional letters.American Morse Code. A dot-and-dash codewhich is commonly used for telegraphiccommunication over wires. It difrers con-siderably from the International MorseCodewhich is used in radio.ammeter. An instrument used for measuringthe current flow in amDeres in a circuit.amp. Ampere.ampere. The practical unit of electric cur-rent flow. The movement of 6,280,000,000,000,000,000electrons past a given point ina circuit in one second corresponds to acurrent of one ampere. When a one ohmresistance is connected o a one volt source,one ampere will flow.ampere-hour. A current of one ampere flow-ing for one hour. This unit is used chieflyto indicate the amount oY electrical energya storage battery can deliver before itneeds recharging.amplification. The process of increasing thestrength (current, voltage or power) of asignal. Amplification can be provided bytransformers and feed-back circuits aswell as vacuum tubes,amplification factor. A vacuum tube ratingindicating the theoretical maximum in-crease in signal strength which can beprovided by a given tube.amplifier. A device consisting of one or morevacuum tubes and associated parts, usedto increase the strength of a signal.amplify" To increase in strength.amplitude modulation. The common systemof radio broadcasting, in which the devia-tion in frequency above and below the as-signed carrier frequency value is equal tothe frequency of the sound wave being'4

transmitted. The amplitude of the trans-mitted signal varies in accordance withthe instantaneous amplitude of the soundwave being transmitted. Abbreviated asa.m., a-m or AM.analyzer. A test instrument used for check-ing radio parts and circuits. It sometimesincludes a special plug-in system whichcan be inserted in a tube socket to extendthe socket terminals for convenience inmaking measurements.anode. The radio tube electrode to which themain electron stream flows. The anode isalso called the plate, and is usually placedat a high positive potential with respect tothe cathode. It is usually identified on dia-grams by the letter P.ant. Antenna.antenna. A metallic structure or an arrange-ment of conducting wires or rods used forpicking up or radiating radio waves. Alsoknorn'nas an aerial.

antenna coil. That coil in a radio receiverthrough which the antenna cunent flows.This coil is usually directly connected tothe antenna and ground terminals insidethe set.armature. Usually the movable portion of amagnetic circuit, such as the rotating sec-tion of a generator or motor, the pivotediron portion of a magnetic loudspeaker, orthe spring-mounted iron portion of a buz-zer or relay.aspect ratio. In television, a numerical ratioequal to picture width divided by pictureheight.atmospheric interference. Cracking and hiss-ing noises reproduced in the radio loud-speakcr due to electrical disturbancesoccurring in the atmosphere surroundingthe earth; these disturbances radiate elec-tro-magnetic waves which are picked upby antenna systems of receivers. Alsocalled static interference, and particularlynoticeableduring thunderstorms.atom. One of the elemental narticles intowhich all matter is divided. An atom has anucleus consisting of electrons and protons,rvith additional electrons revolvinE aroundthe nucleus. Each of the 93 known ele-ments has a difrerent number and anange-ment of electrons and protons in its atoms.attenuation, Reduction in the strength ofan electrical impulse.audible. Capable of being heard by thehuman ear.audio amplifier. A vacuum tube devicewhichincreases the voltage and power of anaudio frequency signal. It may be a sepa-rate piece of equipment or a section in aradio receiver.audio frequency. A frequency correspondingto an audible sound wave. The extremelimits of audio frequencies vary with theindividual and are from about 20 cycles toabout 20,000cycles per second.audio transformer. An iron-core transformer used or thedual purpose of coupling to-gether two audio amplifiercircuits and changing thevalue of an audio signal.


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audio oscillator. An oscillator which gener-ates audio frequency voltages.automatic bass compensation. A special re-sistor and condenser circuit used in someradio receivers to make low audio fre-quency notes sound more natural at lowvolume control settings. The circuit auto-matically compensates for the poor re-sponse of the human ear to weak low-fre-quency sounos.automatic brightness control. A circuit whichautomatically keeps the average bright-ness of the reproduced image constant ina television receiver.automatic frequency control. A special radiocircuit which keeps a superheterodyne re-ceiver tuned accurately to a given station.Used chiefly on push-button tuned re-ceivers to correct slight inaccuracies inoperation of the automatic tuning system.automatic record changer. An electricallyoperated mechanism which automatically

B-. (B negative or B minus.) Symbol usedto designate the point in a circuit to whichthe negative terminal of the plate supplyis to be connected.B+. (B positive or B plus.) Symbol usedto desiEnate the point in a circuit to whichthe poiitive terminal of the plate supplyis to be connected.background noise. Noise heard along with areciived radio program, due to atmosphericinterference or to circuit conditions.baffie. A wood, metal or composition hornor flat surface used with a loudspeaker toincrease the length of the air path fromthe front to the back of the loudspeakerdiaphragm, thereby reducing interactionbetween sound waves produced simultane-ouslv bv front and back surfaces of thediapirralm. A baffie thus serves to directthe sound produced by a loudspeaker andimnrove the fidelitv of reproduction.bakel:ite. A phenolic-"'ompound having highelectrical resistance, used as an insulatingmaterial in the construction of radio partssuch as panels,coil forms, tube sockets,etc.balanced armature unit. An electro-magneticsound-producing device used chiefly inmagnetic loudspeakers. It has a small mov-ing iron armature which is surrounded bywindings carrying audio cunents. The ar-mature is pivoted between the poles of apermanent magnet. Variations in the audiocurrent cause corresponding changes inmagnetism, making the armature rockback and forth. A diaphragm coupled tothe armature produces sound waves.ballast resistor. A special type of resistorused in radio apparatus to compensate forfluctuations in a.c. power line voltage. It

B

feeds, plays and rejects a number ofrecords in sequence. Consists of a motor,turntable, pickup arm and changer mech-anism.automatic tuning. An electrical, electro-mechanical or mechanical system whichtunes a radio receiver automatically to apredetermined station when a button orlever is pushed.automatic volume control. A radio circuitwhich automatically maintains the outputvalue of a radio receiver constant withinlimits while the carrier signal picked upby the antenna is varying in amplitudeover a wide range. It is used in practicallyall modern receivers, for it minimizes an-noying fading of distant stations and pre-vents blasting when tuning suddenly froma weak station to a strong station.automatic volume expansion. A special audiocircuit which increases the volume rangeof a radio program or phonograph record

by making the weak passagesweaker andthe loud passages ouder.a.v.c. Automatic volume control.aviation channels. Frequency bands assignedto aviation service for radio communica-tion between aircraft and ground stations.These bands are both above and belowbroadcast-band f requencies.

is usually connected in series with thepower supply to the receiver or amplifier.The ohmic value of a ballast resistor in-creases automatically with increases incurrent through it, thereby tending tomaintain essential constant cunent de-spite variations in line voltage.ballast tube. A ballast resistor mounted in anevacuated glass or metal envelope. Thisconstruction improves the automatic volt-age regulating-action by reducing radia-tion of heat from the resistor element.band. In radio, frequencies which are withintwo definite limits and are used for a defi-nite purpose. Thus, the standard broadcastband extends from 550 kc. to 1600 kc.B. & S. gauge. Brown and Sharpe wireg:auge, the standard gauge used in theUnited States to specify wire. sizes.band switch. A switch which simultaneouslychanges all tuning circuits of a radio re-ceiver or transmitter to a desired band offreouencies.bandsirread tuning control. A small variablecondenser connected in oarallel with themain tuning condenser of a short-wave re-ceiver to provide more accurate tuning.bantam tube. A compactly de-signed tube having a standardoctal base but a considerablysmaller glass envelope han doesa standard glass tube. Bantamtubes are usedchiefly in compacttable model receivers and in bat-tery-operated portable sets.bantam jr. tube. An extremelysmall glass vacuum tube with aspecial bantam jr. base, usedchiefly in hearing aid units.

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bass. Low audio frequencies.bass control. A manually-adjusted controlorovided on a radio receiver for the pur-'pose of emphasizing the loudness of thebass notes in a radio Program.bass compensation. Any means of offsettingthe natural drop in the response of -thehuman ear to low audio frequencies at lowvolume levels.bass resDonse. The ability of a loudspeakerto handle low audio notes, or the sensitivityof the human ear to low audio notes.battery. One or more dry cells or storagecells connected together to serve as a d.c'voltage source.batteryleceiver. A receiver which uses bat-teries as a Power source.bayonet base. A tYPe of tube andiamp base having two Projectingpini on opposite sides of thesmooth cylindrical base; these en-gage in cbrresponding slots in the

blockins condenser. Any condenserused in aladiJcircuit to block the flow of directcurrent while allowing a.c. signals toDass.bl6oner. Slang term applied to a regenera-tive receivei which radiates a signal whenimnroperlv tuned.body^caiaciiy. The capacity existing-betu'centle human body and a piece of radio appa-ratus.bonding. Connecting the metal,housings andshiel-dsof radio parts together or,to thechassis with heavy wire so they will be atthe same potential (usually ground poten-tial.)breakdown voltage. The voltage at which th.einsulation between two onductors wlllbreak down.briehtness control. In a television receiver,tEe control which varies the average illu-mination of the reproduced image. - - -broadcast. A radio transmission intended forreception by the general Public.broadcasting. A general term applyrng tothe radiation of radio waves carrying pro-grams intended for public interest, educa-tion. or entertainment.broadcast band. The band of frequencies be-trveen 550 kc. and 1600 kc., to which areassiEned all standard broadcast stationsoner-atinE n the United States'broidcast Etation. A radio station used fortransmitting programs to the generalnublic.br6ad tuning. A condition wherein two ormore statiins are picked up at one setting^of a receiver tunlng dial, due to lack ofselectivitv in the tuning circuits.brush. A m-etalor carbon block used to makecontact with a rotating or otherwise mov-ing part in an electrical cirrcuit.buck. To oppose.bufrer. Anv part or circuit used to redueeundesirabldinteraction between radio cir-cuits.bufrer condenser. Any condenser connectedin an electronic circuit for the purposeof reducing peak or surge voltage ?mp-Ii-tude in protection to other parts in thesame or following circuits.bnfrer stage. An amplifier stage used to ple-vent feed-back of energy from a powerstage to a Preceding stage.bus. A semi-automatic codetransmittingkey inwhich 14movement of a lever toonesideproducesa seriesof dots, ind movement to

inE d.c. voltages to the plate and screengr-id electrodei of radio tubes used in bat-tery-operated equiPment.beam-power amplifier tube. 4 special typeof vacuum tube designed for use in theoutput stage of a radio receiver. Deflectingelecirodes-concentrate the electrons intobeams to give high power output alongwith desirable operating characterrstrcs.beat-frequency.The frequency obtained whensiEnals of two different frequencies areco-mbined nd rectified' The beat frequencyis eeual in numerical value to the differ-ence'between the original frequencies.'beat-frequency oscillator. An audio-fre-ouencv osciilator whose output is obtained6v coinbininE and rectifying two knownhigher-frequency signals which are gener-atEd by or obtained -from separate circuits.B eliminitor. An a.c. power pack which con-verts a.c, power line voltage to the pured.c. voltagis required by plate and sc-reen

erid circuits of radio tubes, thereby ellml-iating the need for B batteries.bell wir:e. A common term for the cotton-coveredB. & S. No. 18 copper wire used fo rmaking doorbell and thermostat connec-tions in homes.bias. The fixed voltage applied between thecontrol erid and cathode electrodes of aradio tu6e. Also called C bias.

bayonet-shell socket.B battery. A batterY.ttu"y. A battery having -many smallcells connected in series, used for supply-

bias cell. A tiny 1-volt or 7r/+-voltcell used singly or in series to pro-vide a nesative C bias voltage fora vacuuti tube amplifier circuit.It will last indefinitely if not over-loaded.blasting. Overloading of an amplifier or loud-speaker, resulting in severe distortion orloud sounds.bleeder current. A current drawn continu-ously from a power pack to improve itsvoltage regulation or to increase the volt-ase diop value across a particular resistor.blee-der &istor. A resistor which is used todraw a fixed bleeder current.

6

the other side produces a single dash.built-in aerial. An aerial which is an integralnart of a radio receiver. It may be a loopierial, a power line connection or a sheetof meial mounted in the receiver cabinet'buzzer. An electromagnetic device in whichattraction of an armature by an electro-magnet interrupts the curien-t flow; aa B r r e L l I l Le [ r u l r L s l r r csnrine then pulli the armature back, clos-ine t[e circrlit aeain so that the processing tf,e circuit a_gain so that the proces-sing the circuit agarn so tnaf, tne processre6eats itself and creates a buzzing sound.BX. - Flexible metal conduit used to protectpower Iine wiring in buildings and in high-power radio aDparatus.


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by-pass condenser. A condenser used to pro-vide a low-impedance path for radio orcC. Letter used to designate a condenser, agrid bias voltage, or the centigrade tem-nerature scale.C-. (C negative or C minus.) Symbol used

to designate the point in a vacuum tubecircr:rit to which a negative terminal ofthe grid bias source is to be connected.C+. (C positive or C plus.) Symbol usedto designate the point in a vacuum tubecircuit to which the positive terminal ofthe grid bias source is to be connected.cadmium. A metal sometimes plated on asteel chassis o improve i ts app-earance ndprevent rusting.call letters. Government-assigned identifyingletters for a radio station.cam. An irregular-shaped rotating or slidingpart used to convert rotary motion to lin-ear motion, or vice versa. Used extensivelyin mechanical push-button tuning systems.capacitance. Electrostatic capacity.capacitor. Condenser.capacity. The electrical size of a condenser,determining the amount of electrical ener-gy which can be stored in a condenser bya given voltage. In radio 'lvork, capacityis measured in microfarads (mfd.) andmicro-microfarads (mmfd.) ; 1 mfd. isequal to 1,000,000mmfd.capacitive coupling. A tyae of coupling inwhich a condenser provides a direct pathfor signal energy between two circuits.capacitive reactance. The reactanee which acondenser offers to a.c. or pulsating d.c.It is measured in ohms, and decreases asfrequency and capacity are increased.carbon. An element used in the constructionof radio parts such as resistors, dry cells,and microphones.carbon resistor. A resistor made of carbonparticles and a ceramic binder molded intoa cylindrical shape, with leads attached toopposite ends.

carborundum. A compound of carbon andsilieon used in crystal form to rectify ordetect radio rvaves,as in a crystal detector.carrier. A current, voltage or radio wavehaving the assigned frequency of a radio

audio signals around a resistor or betweena circuit terminal and ground.

station, When no sounds are being trans-mitted, such as during a pause betweenportions of a program, only the unmodu-lated carrier signal is present in the trans-mitting and receiving system.carrier frequency. The frequency of theoriginal unmodulated radio wave producedby a transmitter. In the case of a broadcaststation, the carrier frequency must bemaintained within a few cycles of the fre-quency value assigned to that station bythe Federal Communications Commission,cathode The electron-emitting electrode ofa radio tube. Thermicnic vacuum tubes em-ploy heated cathodes; the heat is eithersupplied indirectly by a filament locatedinside the cathode, or is supplied by cur-rent flowing through the cathode itself.In this latter case, the cathode is also thefilament.cathode ray. A ray or beam of electronsemitted from a cathode,cathode ray tube. A special type of vacuumtube in which a beam of electrons is di-rected at a fluorescent screen by an elec-tron gun, producing a green or white glowon the screen at the point of impact. Thebeam passes between electrostatic deflect-ing plates or electromagnetic deflectingcoils which can make it bend enough toproduce any desired pattern or picture onthe screen when the proper varying volt-ages are applied to the deflecting system.

( l ) Cathode Ray Osc i l l oscope.(2) Ca thode Ray Tun inq Ind i ca ior .(3) Cathode Ray Television Tube.cathode ray television tube. The cathode raytube used in modern television receivers toreproduce the scenesbeing transmitted.cathode ray tuning indicator. A small cathoderay tube used in radio receivers to indicatewhen a station is tuned in accuratbly.cathode ray oscilloscope. A test instrumentusing a cathode ray tube to make visiblethe wave form of a varying current orvoltage.catwhisker. A small, sharply pointed wireused in a crystal detector to make contactwith a sensitive point on the surface ofthe crystalC battery. The battery used for supplying anegative C bias to the control grid of avacuum tube.C bias. An applied voltage used to make thecontrol grid of a vacuum tube negative'with respect to the cathode.

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cell. A single unit capable of serving as ad.c. voltage source. A primary cell, suchas a dry cell, cannot be recharged whenexhausted. A secondary cell, such as thecell of a storage battery, can be rechargedwhen exhausted by passing a currentthrough it in the reverse direction.centering control. In a television receiver, acontrol used to shift the entire reproducedimage on the screen. The horizontal cen-tering control moves the image horizon-tally in either direction, while the verticalcentering control shifts the image up ordown.Centigrade. The European scale of tempera-ture in which 0 is the temperature of melt-ing ice and 100 is the temperature ofboiling water, at sea level.centimeter. In the metric system of measure-ments, a unit equal to one-hundredth of ameter, or approximately .39 inch. Thereate 2.54 centimeters in one inch.chain. In radio, a network of radio stationsconnected together by special telephonelines so that all can broadcast simultane-ously a program originating at a keystudio.channel. A narrow band of frequencies in-cluding the assigned carrier frequency,rvithin which a radio s.tption is required tokeep its modulated caffiicr signal in orderto nrevent interference with stations onadjicent channels. Also, one branch orpath over which radio signals may travel;thus, a p,a. system may have several inputchannels, each with its own sound pick-up device, transmission line and volumecontrol.charge. A quantity of electrical energy heldon an insulated object. The electrical ener-gy stored in a condenser. The act of sup-plying electrical energy to a metal object,to a condenser, or to a storage battery.When an object has more electrons thannormal, it has a negative charge. When anobject has less electrons than normal, ithas a positive charge.charger. A device used to convert alternatingcurrent into a pulsating direct currentwhich can be used for charging an ex-hausted storage battery.chassis. The metal framework on which theparts of a radio receiver or transmitterire mounted. Also used to designate thecompleted piece of radio equipment beforeit is mounted in a cabinet.choke coil. A coil used to limit the flow ofalternating current while allowing directcurrent to pass. R,F. choke coilS have ai ror pulverized iron cores, while a.f. chokecoils and filter chokes have iron cores.

circuit. A complete path over which an elec-tric current can flow.clip. A small spring-type clamp having anyof several different designs, used for mak-8

ing a readily removable connection to aterminal.clockwise. The direction in which the handsof a clock move.coaxial cable. A two-conductor cable in whichone conductor is a flexible or non-flexiblemetal tube and the other is a wire centrallysupported inside the tube by insulators.cm. Centimeter.code. A system of dot and dash signals usedin the transmission of messages by radioor wire telegraphy. The InternationalMorse Code (also called the ContinentalCode) is used everywhere for radio tel-egraphy. The American Morse Code isused commonly for wire telegraphy.code recorder. An instrument which makesa permanent record of code messages re-ceived by radio or otherwise,coil. A number of turns of wire wound onan iron core or on a coil form made ofinsulating material. A coil offers consider-able opposition to the passage of alternat-ing current but very little opposition todirect current.coil form. The tubing or solid object onwhich a coil is wound. It can have anyshapeand can be made from any insulatingmaterial, such as paper, cardboard, fiber,bakeli te, a plastic or ceramic material,or wood.cold cathode. A cathode which does not de-pend upon heat for electron emission. Thecold cathode of a photoelectric tube emitselectrons when exposed to light, while ina type BH rectifier tube the electrons arepulled out of the cold cathode by a suffi-ciently high voltage applied to the pointedanode.color code. Any system of colors used tospecify the electrical value of a radio partor identify terminals and leads.communication receiver. A receiver designedespecially for reception of code or voicemessages ransmitted by short-wave radio 'communlca ron servlces.

concentric cable. Coaxial cable.condenser. A radio part consisting of twoconducting surfaces separated from eachother by an insulating material such asair, oil, paper, glass or mica. A condenseris capable of storing electrical energy. Inradio circuits, condensersare used to blockthe flow of direct current while allowingalternating and pulsating currents to pass.The electrical size or capacity of a con-denser is specified in microfarads andmicro-microfarads.conductivity. The ability of a material to


11/39

carry electric current.conductor. A wire or other metal structurervhich provides a path for electric .""";;ibetween two points. A conductor is thus amaterial which offers little opposition tothe continuous flow of electric'current. --cone. The co-nical-shaped aper or fiber dia_phragm ot a magnetic or dynamic loud_speaker.console.- A large radio receiver cabinet, de_srgneq to rest on the floor rather than ona table.contact. A terminal to which a connectioncan be nrade. A joining of bodies o permiithe flow of electrical current.Co_ntinental Code. Same as the InternationalMorse Code. Used universalty for "adiotelegraphy.contrast control. In a television receiver. amanual control which adjusts the ranEe'oibrightness between highlights a"a .t aEo*.of tle reproduced image.cont-r'ol rid. That electrode in a vacuum tubewhich has the most effective co"i"ot o""rithe plate current passed by the tube. Checontrol grid is usually the electrodenealestto the cathode.converter. That sectionof a superheterodvneradio- receiver which changes i"c"m"inEmodulated r.f. signals to a loiler frequen;iknown as the i.f. value; the converter sec-_tion includes the oscillator and the firstdetector. Also,.a_device, usually "otu.V,cnanglng electncal energy from one fornrto another, as AC to DC-,-etc.copper-oxide rectifier. A r.e6tifier made up ofdiscs of copper coated on one side ri,iihcuprous oxide. The discs allow direct cur_rynt to flow in one direction but allow vervlittle current flow in the reverse directiori.core. The center of a coil.counter-clockwise. In a direction oppositethat in which the hands of a clock r tat l .coqntersink. To r.eam, drill or cut a conicjldepression around a hole for a flat_headscrew, so that the screw head will be flushwith the surface of the work.coupling. Th,e means by which signals aletransfened from one-radio circriit to an_othe_r. Coupling can be direct throuEh aconductor,. electro-static through a -con_denser,or inductive through a trinsformer.Also, a connecting device.c.r.o. Cathode ray oicilloscope,crystal. $ nie-ceof natural quartz ol similarplezo-electric material which has beengr_gund o a size which will vibrate natu-rally at a desired radio frequen.v ,nagenerate that flequency wheir sei intovrbratton. A quartz crystal is used n radiotransmltters to generatewith a high degree

of accuracy the assigned carrier frequencvor a statlon, and is used in crystal filfers o- fradig receivers to improv" tt, "et"ciiiii"of the i.f. amplifier. The minerai-ilil 'iia cr-ystal detector is ,known u, u ."y"tui.crystal control. Use of a quartz crysial tornaintain operation of a'radio .a;t i ; ; ; ;rrs assrgned frequency within the limitsprescnbed bv law.crystal detector. A detector uti l izinE a crvs_tal such as silicon o. gut"ru i;";riu.t *iir,a.potntedwire to recti fy an incoming radiosignal. Used in crystairec"i";;;:- ' ' ' - - ' "N rfi;rw @TYPESOF CRYSTALDETECTORS

crystal f i l ter. A highly selective uninE cir_cur employrng-a qvartz crystal, sometimesused ln the i .f. ampli f ier of a communica_trons receiver to improve selectivity so asto permit reception of a desired stationeven when there is strong i"t"rf""Lncefrom other stations on nearb.-yh;;;;i;'""crystal pig\-trp. A type of pnoi,og"rpir-pi"f._up.in rvh_ichhe neehle m-ovemeits'befid-oi,twist a- Rochelle salt crystal ;iemil-;;cause the crystal element to generaie-'aiaxoro rrequency voltage corresponding othe recorded sound rvaves.crystal set. A radioreceiver which usesa crystal detectorfor signal rectifi-cation, and has novacuum tubes.current. The move-ment of electronst h r o u g h a c o n -

db. Decibel.d.c. Direct current.d.c.c. Double cotton covered insulation onwires.d.c. receiver. A receiver designed to operatefrom a d.c. power line, such as froin the110-volt d.c. lines still being used in oldersectionsof some cit ies.

ductor. Current is measured in amperes, inmilliampe-resand in mrcroamperes.cutting_head. That part of a sound lecorderwhlch cuts or embosseson a disc, the ir_regular-grooves corresponding to tile waverorm of the sounds being recorded.c.w. Continuous wave.cycle. One contplete reve.rsal of an alternat_rng current, including a rise to a maximumtn one dlrectron, a return to zero, a riseto a maximum in the other direction, andano_therreturn to zero. The numfe" oicycles oc-curring in one second is tfre i.e_que_ncy f an alternating current. The wordcycle is commonly inlerpreted to meancycles per_s-econd,n which case it is ameasure of frequency.

I)'Arsonval meter movement. Thecommonestmovement employed in precisiondirect cur-rent me.asuling instruments. It consistsessenttally of a small coil of wire supportedon jeweled bearings between the;; i ; ; - ; ia permanent magnet with a spirai sprineholding the coil aid the attactreh-inai;;;i;;pointer at the zero position bn ;il;';;ili

D

9


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scale. When the current to be measured issent through this coil, the magnetic fieldsof the coil and magnet interact to causerotation of the coil and pointer.dead spot. A region in which signals fromcertain radio stations are poorly received.decibel. A unit used for comparing the powerlevel of a signal to a fixed reference levelof power. Also a measure of power, currentor voltaEe Eain.decouplind. A method of isolating individualstages of an amplifier to prevent inter-stage feedback through power supplycircuit.delayed a.v.c. An automatic volume controlcircuit which does not begin to act untilsignals reach a certain strength. It per-mits improved reception of weak signals.definrtion. In television. the clearness withwhich video details are reproduced.degeneration. A type of feed-back whichimproves amplifier quality.

demodulation. The process bf rectifying ordetecting a modulated radio signal in orderto remove the carrier and obtain the de-sired audio or picture signal.detector. That stage in a receiver at whichdemodulation takes place. fn the detectorstage of a t.r.f. receivet, the rJ. signalsare separated from the desired audio sig-nal. In the second detector of a super-heterodyne receiver, the i.f. signals areseparated from the desired audio signal.dial. Any means for indicating the value torvhich a control knob has been adjusted.Tuning dials of broadcast band receiversindicate the frequency to which the re-ceiver is tuned, either in kilocycles directlyor in kilocycle values having one zero re-moved; sometimes the wavelength inmeters will also be indicated.dial cable. The braided cord or flexible wirecable used to make a tuning knob controlthe position of the pointer or dial whichindicateS the frerluency to which a radioreceiver is tuned.dial light. The pilot lamp which illuminatesthe tuning dial of a radio receiver.diaphragm. A thin, flexible metallic or non-metallic sheet which vibrates when struckby sound waves, as in a microphone, orwhieh produces sound waves when movedback and forth at an audio rate, as in aheadphone or loudspeaker.dielectric. The insulating material betweenthe plates of a condenser.diode. A vacuum tube having two electrodes,one being the cathode and the other theplate or anode. A diode allows electrons topass in only one direction, from the cathodeto the anode.

direct coupling. The use of a conductor toconnect two circuits together and providea direct path for signal currents.direct current. An electric cument whichflows in only one direction. It is not neces-sarily constant in value.directional antenna. Any antenna whichpicks up or radiates signals better in ouedirection.direction finder. A special type of radioreceiver employing a highly directionalt 0

loop antenna so as to permit determiningthe direction from which radio waves arearriving.discriminator. In an F.M. receiver, the sec-tion which converts frequency modulatedsignals into audio signals.distortion. Unfaithful reproduction of soundor television signals due to changesoccurring in the wave form of the origi-nating signal somewhere in the course ittakes through the transmitting and receiv-ing system.distributed capacity. Capacity distributed be-tween conducting elements such as wires,as distinguished from capacity concen-trated in a condenser. Usually used tospecify the small capacity existing betweenthe turns of wire in a coil.double-button carbon microphone. A carbonmicrophone employing two buttons or con-tainers for carbon granules, one on eachside of the diaphragm, so as to secure apush-pull action which gives increasedsignal output.double pole srvitch. A switch l'hich simul-taneously opens or closes two separatecircuits or both sides of the same circuit.d o u b l e t h r o wswitch. A switchrvhich connectsone set of ter-minals to eitherof two othersets of terminals. KNIFE TOGGLEdoublet antenna. D.P.D.T. WITCHESAn antenna system with an insulator in-serted at its exact center, with one leadof a two-wire transmission line connectedto each half of the antenna at this in-sulator.d.p.d.t. Double pole, double throw.d.p.s.t. Double pole, single throw.drain. A terrn used to indicate that currentis being taken from a voltage source.driver. A stage of arnplification used to feedor drive a final stage of amplification forthe purpose of making the final stage oper-ate at maximum efficiency.drop. The voltage drop developed across aresistor due to current florv through theresistor.dry cell. A type of primary cell inlvhich theelectrolyte is in the form of a paste ratherthan a liquid. Dry cells are used exten-sively in radio batteries.dry electrolytic condenser. An electro.lyticcondenser in which the electrolyte is apaste rather than a liquid, to permit usingthe condenser n any position rvithout dan-ger of the electrolyte leaking out.

I

ffiWwire.ilummy antenna. A resistor or other devicewhich duplicates the electrical characteris-


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tics of a transmitting antenna rvithout ra -di-ating radio waves. Used for testing andadjusting transmitters.duralumin. An alloy of aluminum which iscomparable in strength and hardness tosoft steel. It contains 95.5 parts alumi-num, 3 parts copper, I parf manganeseand .5 patt maEnesium.DX. A slang expression for distance. usedchiefly in connection with recention ofdistant radio stations.dynamic loudspeaker.A loudspeaker in whichthe diaphragm or cone is- attached to asmall coil mounted so it can move within

E. Commonly used symbol for voltage.eddy currents. Circulating currents inducedin conducting materials by varying mag-netic fields. They are undesirable becauiethey represent loss of energy and causeheating. Eddy currents are kept at a mini-mum by employing laminated constructionfor the iron cores of transformers. a.f.choke coi ls, and other magnetic devices.Ddison base. The standard screw base usedfor ordinary electric light bulbs in thiscounlry.effective current. That value of alternatingcurrcnt lvhich wifl cause the.sam.eheatingeffect as a given value of direct current.For sine wave alternating currents, theeffective value is approximately sevelt-tenths of the neak value.efficiency. The -ratio of energy output toenergy input, usualiy expressed as a per-centage. A perfect electrical device wouldhave an efficiency of 700/o.electralloy. A soft iron alloy used for radiochassis construction.electrical transcription. A disc recording ofa complete program, as contrasted with aphonograph record which ordinarily con-tains only a single musical selection-Transcriptions are made to permit broad-casting of a particular program at anydesired time by any number of stations.

electric eye. Popular expression for a cathoderay tuning indicator tube used in modernradio receiving sets. Consists of a fluo-rescent screen with a dark sector whichvaries in direct proportion with thestrength of the incoming signal. Also usedin connection with photoelectric cells.clectric field. A region in space surroundinga charged object. Lines drarvn to representthe direction in which the electric f ibld wll tact on other charged objects are calledelectric lines of force. A movinE electricfield, such as that associated r ' i thi lectronsin motion or with a radio wave, is alr,vaysaccompanied by a moving magnetic field.electricity. A general term used when refer-ring to the energy associated with elec-trons at rest or in motion.electrode. An essential part inside a vacuumtube, such as the cathode, the variousgrids and the anode. Also, the plates of aprimary cell, secondary cell or electrolytiecondenser.

a conslant magnetic field. Audio frequencvcurrents flowing through this coil [calleitthe voice coil) make it move in and out.thereby causing the diaphraEm to renro-duce sound waves. The-magnetic field isproduced by a permanent miEnet in n.m.dynamic loudspeakers, and by an eleclro_- magnet in electrodynamic oudspeakers.dynamotor. A rotating deviceacti irE both asmotor and generator, used to chaige a d.c.voltage to an a.c. voltage or to a hiEheld.c. voltage. lt is used cEiefly for poit-aUteand mobile operation of radio tranimitiersand P.A. amplifiers from storage Uatieiie.-E

e lec t rodynamie oud-speaker. A dynamicloudspeaker in whichthe constant maeneticfield is produced byan electromagnet. Thecoil of this electro-magnet is known asthe field coil.electrolyte- The liquido r c h e m i c a l D a S t ewhich is used betweenthe electrodes of a dry cell, storage bat-tely or electrolytic condenser.electrolytic condenser. A fixed condenser inwhich the dielectric is a thin fiIm of gasformed on the surface of one aluminirmelectrode by a liquid or paste electrolytc

ELECTROLYTIC ONDENSERl. Cardboard coniainer.2. Wax-impregnaled inner liner.3. Pure wax fi l ler.4. Etched aluminum foil.5. Cellulose seDaralor.6. Terminal lead.7 . Insu la fed u :h -back eads.electronragnet. A coil of wire, usually woundon an iron ^co-re, hich produces i strongmagnetic field when current is senlthrough the coil.electromotive force. Voltage.electron. A small active pirticle of negativeeleetricity- Some electr6ns are closely-asso_ciated with atoms of matter, while t,thlrs,called free_electrons,move readily betweenatoms under the influence of electric orrlagnetic fields. It is the movement ofclectrons through a conductor whictr co"_stltutes an electric current.le_ctronemission. The ejection of electronsfrom the surface of a'materiai i"a;-;;;rounding spa-cedue to heat, Usht. hiEl,voltage or other causes. In a tfiermion"ie

il


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vacuum tube, electron emission from the""ittoa" is froduced by heat from thefilament.electronic control. The control of a machineor device by apparatus employing electrontubes.electronics. A broad field of electricity cov-erinE rvork with all types of apparatusemJlovine electron tubes for industrial,nrilicltio.ts. Radio and television areniajor branches of the electronic field.electrbn tube. Any partly-evacuated' com-nletelv-evacuated or gas-fi l led tube usedio conirol the flow of electrons n a circuit 'Vacuum tubes, phototubes, mercury vaporrectifier tubes and cathode ray tubes areall electron tubes'element. One of the ninety-thlee knoqn basicforms of matter which make up the unl-verse, The term is also used to refer to the

f. f lequency.F. Fahrenhcit. Scaleof temperature.facsirni le.A system of radio conlmunicationin u'hich photographs' drarvings, h-andlvrit-inE. and -printed matter of any kind aretl insnti tted to receivet's which fced intofacsimile recorders.facsimile recorder'.An instrument which re -uroduceson paper thc i l lustration. writ ingir nl inted matter being tt 'ansmitted by afacsimile system.faaing. An cssential ly regular .r is.cand fal ldue to variations in transurrsslon conol-tions along the path taken by the. radiowaves froin the-transmitting station tothe receiver.Iiahnestock clip. A spring-type terminal,.towhich a temporary connectloncan reaolly

F

important parts of a device; thus, thecatlhode,grif and plate would be called theelements of a triode vacuum tube.e.m.f. Electromotive force or voltage.enameled tvire. Wire coated with an insulat-inE layer of baked enamel.energy. -Abil i ty to do wolk. Thus. the elec-triial energy stored in a dry cell has theability to he-ata radio tube fiIament' oper-ale a buzzer, etc.envelope. The glass or metal housing of aradio tube,escutcheon. The ornamental wood, metal ornlastic framework for a radio dial, tuningindicator or other panel-mounted part ina radio receiveror amplif ier.ether. The medium whiih is supposed o fi l lall space, and through which radio, heat'and fiEht wavesare snpposed o travel. I tsexiste"nce as not yet b66ndefinitely proved'

field frequency. In television systems em-ploying interlaced scanning, this term re-fers to the number of times per second heframe area is fractionally scanned.filament. The resistance rvire through whichfilament current is sent in a vacuum tubeto nroduce the heat required for electronemission, When electron emission s fromthe surface of the filament wire itself, thefilament is also serving as the cathode.When the fi lament merely suppliesheat toa senarate cathode electrode. we have aheat6r-type or indirectly-heat6d tube.filament circuit. The complete cir"cuit overwhich fiIament current flows from the Abattery, fiIament winding or other filamentvoltagi' source to the -filament of radiotubes and pilot lamps.filament current. The current supplied to thefllament of a vacuum tube for heatingpurposes.filament voltage. The voltage value whichmust be applied to the filanrent terminalsof a vacuum tube in order to provide'therated value of fiIament current.filament winding. A separate secondarywind-ing provided on the pou'er transformer ofa "riaio receivel oi other a.c.-operatedapparatus for use as a filament voltagesource.filter. A resistor, coil, condenseror any com-bination of these parts which is used toblock or attenuate alternating currents atcertain frequencies while allowing essen-tially unimpeded flow of currents at otherfreouencies or of direct current. Thus, thefilter in a radio power pack is a coil, con-denser and resistor cbmbination which

receives a pulsating direct current havingmany a.c. components, but dglivers an es-sentially pure and constant direct current.filter choke. A ioil used in afilter systeur to pass lowfrequency currents or directcurrent while limiting orblocking the flow of higher-frequency alternating orpulsating currents.

be made.Fahrenheit. The temperature-measurilg s.ys-tem general ly used in the United States'in ivh"ich32 degrees is the temperature ofmelting ice and 212 is the temperature ofboi l ine water at sea level.farad. the basic unit of capacity, but toolarEe for practical use. The microfarad,eoo-"alo one millionth of a farad, is a morepiactical unit for radio work. An evenimaller unit, the micro-microfarad, - isut.o u."d in iadio; it is equal to one mil-lionth of a microfarad.F.C,C. Federal Communications Commission'A commission appointed by the Presidentof the United States possessing icensin-gand resulating authority on matters deat-inE u'i [h wire and radio communication nthE United States and its possessions.feedback. Transfer of energy from.one pointin an electrical system to -aprecedrngpornt'such as from the output back to tne lnpuf,'fideiity. The faithfulness with which part orrtt bt u" electrical system delivers a re-production of the input signal wave form'field. The effect produced in surrounding--iou"" bv an electrically charged object' byeiectrons in motion, or bY a magnet'field coil. In an electrodynarnic loudspeaker'the coil which produces the constant-strength magnetic field.

l 2


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l ifilter condenser. A condenserused in a filtersystem to permit passage of hiEher_fie_q.uengy urrents while l imiting or blockingthe flpw of lower-frequency currents anddirect current.f irst augio stage. The fi r .ststage in the audioamplif ier of a radio receiver.-Audl"-. i*"" i ,are-fed into this stage by the d;6;tor';i;t.r.f. receiver, and biy tfi" ;;";;,i;-"t";;";^ or a superheterodyne eceiver.nrst detector. That stage in a superhetero_dyne- eceiver in rvh cii the-i;."--i;;;;;;_Iated r.f . signal and tt," . . t . . ic;i l" i ;;;the lo-caloscillator u"" "o.,rtl-nuJ;il;*ffi;the i.f. sienal.f ixed condenser, A contlenserhavinq a defi_nite capaciry value which ;;;;;i fr"";;_.lusted.fixe.d resistor. A resistor having a definiteohmic value which cannot n" ia:"J"i.^'"'.----_q@#__

fluorescent screen. A coating of chemicalmaterial w-hichglows .ut"n"Uo*UurJ"J i l ,electrons. ln a cathoderay tube. the coat"_ing,is -on the inside .urfuin-oi inu';;;;;_- ate9.Slassenvelopeof the tube,r.m. .t requencymodulation. Also written as. f-m or FM. See frequency nrodulal ion.rocusrng control. In a cathode ray osci l lo_sc-ope or television system, the controlrvhich adjusts the size"of t tr" i , l . ibi" ' .rJip_r9dyc5d t the screen by the el;;l;;;;;;^ tn a cathode ay tube.trame. ln televisio-n, ne complete scanninEor ever.y part of the field of view beinfitransmitted.frame. frequency. In television, the number;i"*1f'.Xr";f""d:ond the frame area is com-framing co_ntrol. In television, a generalterm applying to any of the controTknob.sused, or_ adjusting'th" a;t"r;;; ' ; i ; ; ;" and height of the r:Lproducedmaie. ' '""fre^e electrons. Those electrtnr".i,ii.f, r. "free to move between the atorns.of-;;";;:rial w^henacted upon oy electrrc or maE_netic forces.frequency. The _number of complete cyclesper second which an electrtc current_ asound wave or a vibratins .b;".f ^,;;dlrlg9 -s;,r,reqgency is_equal "to i"h;;;t".i;- otvlded by the wavelength.frequer]cy- converter. A circuit or devicewhich changes the frequen.v of an utiurl

gain,. In an amplif ier stage or system, theratio of output voltage, current or powerro rnput voltage, current or power. Uiual lyexpressed in decibels.galena. I ead sulphide, a shiny bluish sravmlnerat often used as the crystal i-n icrystal detector.gang switch. Two or more rotary switchesmounted on the same shaft anf ;il;;l;;by a single control.gan_g uning condenser. Two or more vari_able tulin-g condensers mounted on thesame shaft and operated bV a slngiecontrol.

na.trng current. Thus, the oscillator andmixer first-detector stages make ;; ;i;;frequency converter oI ; .;p-;*t;i""5avii"receiver.frequelcy distortion. A type of distortionwlich occurs when a "i", i i i i * a""i ;;;:plifies or transmits onequriiv it " ;;it;;;afrequencies t is handlingfrequency modulation. A relativelv new svs-9m. for radio broadcasting peifected "tvMajor E. H. Armstrong,-ifr-i"ti"rr*il iamount of deviation in t.equ"rrcy aboveand belorv the resting frequencv is"ri;;;iinstant proportional-to tle airpl i t"d;;irne sound rvave being transmilted. Thenumber of complete "aev.iitions -p;; "; ;old abo-ve and - below the restinE ?re_quency is equal to the ftequency ;f -thesound wave being transmitted.Advantages of this system include almostcomplete freedom from atmospt";i;- ;;;

rnan-made interference, u. *uil ",-litti;

or no interference between .tution". tf,"lulby permitting the transmisit""-;i"; "m"u:c"hgreater volume range and a wiaur a"aiorrequency range than is possible withamplrtude modulation. One disadvantaseis the necessity of empiovi"e-ri t""_hlFicarrler lrequ-enc.ies, t rvhich fhe ranEe "ofa srar,ton s l lmrted to approximatelt 100miles.frequency response.A rating or graph whichexpresses he manner in rvhich'a di icrrt-."de-vice handles the aiff""u"i - f"equ"i'.il"fal l ing within its operat;ns-iangJ-t;;..rne rrequency- .esponse f a loudspeakeimay p^espe_cified s being essentiailv flator uniform between r0o aid 6000 t;i;s:^*'full-wave rectifier. A radio tube or otherdevice which rectifies u" uti"r"uti"""""._rent in such a way that tottr hai%s "o teacn rnpuf a.c. cycle appear in the pulsat_lng rectried output. A full_wave rectifierruDecontalns two separate diode sections.p,L:-p-1...r1,9current during one alternairron, and the other nassing current duringthe opposite half cycle.

fuse. A .protective device consistine of asnort preceof wire which melts and breakswhen the current through it ";;;";;;ii;rated_valueof the fuse. Fo.u" u"" i".""i din radi,o circuits to open tt " .i".ril"".ri"]marleal ly ln case of serious overload.thereby preventing damage 6 p";#;rne clrcurt.G

GANG SWITCH(ROTARY) GANG TUNINGCONDENSERgaseous ube. An electronic tube into which3 tmull amount of gas or.vapo" ir-aa*i lCted. after the_tubJhas, peen evacuated.ilii= lil" i:"^.ffi'?',""'":'-lge-:l:reased current flow. t 3


16/39

generator. A rotating machine which con-verts mechanical energy into electricalenergy. Also, a radio device or circuitwhich-develops an a.c. voltage at a desiredfrequency when energized with d.c. orlow-frequency a.c. power.getter. An alkali metal introduced into avacuum tube during manufacture and va-porized after the tube has been evacuated,to absorb any gases which may have beenleft by the vacuum pump. The silverydeposit on the inside of the glass envelopeof-a tube, usually near the tube base, isthe result of getter vaporization.ghost image. In television, an undesiredduplicate image appearing a fraction ofan inch to one side of the desired image,due to reception of a reflected signal alongwith the signal coming directly from thetelevision station. The remedy involvesusinE a directional receiving antenna ad-justed so it rvi l l receive signals comingover only one path.glass-type tube. A vacuum tube or gaseoustube having a glass envelope or housing.glow lamp. A gaseous ube havinga glass envelope hrough whichcan be seen a glow due to ioniza-tion of the molecules of gas.Neon gas gives a.red glow, rner-cury vapoigives blue, and argonEas Eives a liEht purple Elow.

grid condenser. A small fixed condenser in-serted in the grid circuit ofa vacuum tube.grid leak. A resistor of high ohmic value,used to connect the control grid to thecathode in a grid leak-condenser detectorcircuit.grid leak-condenserdetector. A type of de-tection in which a.f. potentials developedacross a grid resistor by the flow of gridcurrent through that resistor result inplate current changes at the desired aqdiofrequencies. This type of detector is iden-tified by the presenie of a grid leak andgrid condenser n the grid circuit.grid return. The lead or connection whichprovides a path for electrons from the gridiircuit or C bias battery to the cathode.grille. An arrangement of wood or metal- bars placed across the front of the loud-speaker in a radio receiver for protectivepurposes and to enhance the design of thecabinet.

grille cloth. A loosely woven cloth stretch,ed- behind the loudspeaker gl i l le of a radioreceiver to keep dust and other foreigumatter out of the loudspeaker, as well asto conceal the loudspeaker diaphragm.Sound waves travel unimpeded throughthis cloth.grommet. A special washer' made oJ rubberor other insulating material, used to pre-vent a wire from touching the sides of achassis hole through which the wire is run.ground clamp. A metal strap or clamp usedfor making a good electrical connection toa ground rod or grounded pipe. The clamphas a screw terminal or soldering lug towhich the ground wire of a radio receivercan readily be attached.ground wire. The wire used to connect theground terminal of a radio receiver ortlansmitter to a ground clamp or other. grounded object.ground waves. Radio waves which travel- along the surface of the earth instead ofgoing up into the skY.guy wire. A wire used to brace the mast oriower of a transmitting or receiving an-tenna system.Huses Hazeltine patents under a licensingagreementwith the Hazeltine Corporation.n";fl8l31l",*,.,;:i3'l*""',l:;the ear by a clamp passingover the head. Used forprivate recept-ion of radioprograms or for recePtionof siEnals which are toorveak-to provide loudspeak-er volum6. Headphonesare usually used npairs, one for eaoh ear, with the clampingstlap holding them both in position.heater. A filament used in a vacuum tubeonly for the purpose of supplying heat toan indirectly heated cathode.Heaviside layer. A layer of ionized gas rvhichscientists believe exists in the region be-tween 50 and 400 miles above the surface

gas gives a light purple glow.AIso called Elow tube.Iso called glow tube.gram. The unit of weight in the metric sys-- tem. One pound is equal to 453 grams.grid. An electrode mounted between thecathode and the anode of a radio or elec-tronic tube to control the flow of electrons{rom cathode to anode. The grid electrodeis usually either a cylindrical-shaped wirescreen or a spiral of wire through lvhichelectrons can readily move.grid bias. Another term for C bias, whichis the voltage used to make the controlgrid of a radio tube negative with respectto the cathode.grip cl ip. A spring cl ip used o makean easi ly removable connection othe cap terminal located at the toPof some radio tubes.

half-wave rectifier. A radio tube or otherdevice which converts alternating currentinto pulsatinE direct current by allowingcurrent to pass only dul ing one half ofeach alternating current cycle' A half-wave rectifier tube contains only one diodesectior:.harmonic. A multiple of any particular fre-ouencv. Thus. the secondharmonic of afindainental frequency would be equal totwo times that fundamental frequency.harmonic distortion. Another name forwave form distortion.Hartley oscillator. A vacuum tube oscillatorcircuit identiffed by a tuned circuit whichemploys a tapped winding connected be-tween the grid and plate of the vacuumtube, with the tap going to the cathode.Hazeltine licensed. Radio apparatus whicht4


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l i

of the earth, and which reflects radio wavesback to earth under certain conditions.Also called the Kennelly-Heaviside layer.henry. The practical unit of inductance.high-fidelity receiver. A receiver capable ofreproducing audio frequencies in a rangefrom 50 to about 8,000cycles or wider with-out serious distortion. A receiver whichapploaches the goal wherein the repro-duced program cannot be distinguishedfrom the original studio program.high-frequency trimmer. In a superhetero-dyne receiver, the trimmer condenserwhich controls the calibration of a tuningcircuit at the high-frequency end of a tun-rng range.hold controls. In a television receiver, thetwo manually-adjusted controls which ad-just the natural oscillating frequencies ofthe oscillators employed in the horizontaland vertical sweep circuits.hook-up. A diagram giving circuit connec-

I. Commonly used to designate eurrent.iconoscope. A cathode ray television pick-uptube for use in electronic televisioncameras. It converts each tone value of thescene being televised into a correspondingelectrical impulse. Scanning of the imageis accomplished by sweeping an electronbeam rapidly back and forth across thel ight sensitive mosiac screen.

i.f. Intermediate frequency.image. An interfering signal whose fre-quency is twice the I.F. frequency aboveor below the wanted siEnal.image dissector. A catho-de ray televisionpickup tube. Construction and operatingprinciples are different from those of theiconoscope,but serves essentially the samepurpose of converting a scene into corre-sponding electrical impulses.image ratio. The ratio of the strength of asignal to its image. Used to indicate selec-tivity of a receiver,image reconstructor. The cathode ray tubeused in a television receiver to convertreceived signals to original picture.impedance. The total opposition which aradio nart or circuit offers to the flow ofalternating or pulsating direct current ata particuiar frequency. Impedance is acombination of resistance and reactance,and is measured in ohms.impulse. A sudden momentary increase inthe current or voltage in a circuit.

tions for a radio receiver, amplifier ortransmitter.hot-cathode tube. A vacuum or gaseous tubein rvhich the cathode is heated to provideelectron emission.howl. An undesirable audio frequency oseil-lation occurring in a radio or arnplifiersystem, due either to electrical or acousticfeedback.hum. A low and constant audio frequency,usually either 60 to 120 cycles, heard inthe background of a received radio pro-gram. A defective filter condenser in ana.c.power pack is a common causeof humin a radio receiver.hysteresis. Failure of the maEnetic flux toincrease or decrease mmediately in ac-cordance with changes in the rnagnetizingforce acting on a magnetic materlal. Thi ilag in the magnetization causes osses niron-core transformers which are knownas hysteresis osses.

indoor antenna. A reeeivinEantenna svstemlocated entirely inside i bui ldinE. eitherynder a rug, around the walls of a room,between the walls, or in the attic.induced voltage. A voltage produced in acircuit by changes n the number of mas-netic l ines of force which are l inkinE 6rcutting across the conductors of the--cir-cult.inductance, That property of a coi l or othelraclio part which tends to prevent anvchange in current florv. Inductance is ef-fective. only when varying or alternatingcurrents are present; it has no effectlvhatsoever upon the flow of direct cur_rent. Inductance is measured in henrvs.inducl ion. An action whereby the variableflow of current through one coil producesa. voltage in _a nearby coil even thoughthere is no electrical connection betwe"enthe coils.,.The coupling is produced bymagnettc l lnes ot rorce.inductive coupling. A form of couplinE inrvhich energy is transferred from i coi l inone circuit to a coi l in another circuit bvinduction. Magnetic lines of forc.c pro"-du.ced y the flow of current through-onecoil cause an a.c. voltage to be induled inthe other coi l .inductive reactance. Reactance due to theinductance of a coil or other part in analternating current circuit. Inductive re-actance is measured in ohms, and is eoualto the inductance in henrys multiplied bythe frequency in cycles, times the numbei'6.28; inductive reactance therefore in-creases with frequency.insulation. Any material u'hich has a suffi-ciently high electrical resistance to permitits use for separating one electric-al cir-cuit, _pa_rtor wire from others. Cotton,silk, baked_enamel, mica, porcelain, rub-ber and bakeli te are a few of the'com-mon insulating materials used in radio.intelligence signal. Any signal which con-veys information, such as voice. nrusic.code, television pictures, facsimile photo-

t 5


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giaphs, diagrams, written and printedmatter, etc.intermediate frequency transformer. -44a*o'T,l,r1i1"i'.""i ?,iiiH*cmtage in a superheteroavnee-llNElniilfilceiver or-. oupling.lYllosesandJINmuilr||. for providingselectivity.,___- "llffiH lllllintermittentreception.. ,1. tVPgolllSQEilllradio receiver trouble in which I altz'the receiver performs normally for a time,

then becomes dead or distorts the pro-grams, with the process repeating itself'lnternational ]Vlorse Code. The code useduniversally for radio telegraphy, and alsoused for wire telegraphy in some E-urop^eancountries. It is also known as the Uon-tinental Code.inverse feedback. Intentional negative feed-back or degeneration, introduced in an am-nlifier or si-inEleacuum tube stage for the-purpose of reducing distortion, therebypermitting greater po,wer output. -inierted L antenna. The conventional an-tenna used for broadcast reception, havinga lonq horizontal portion suspended be-tweeri insulators, with the single wirelead-in connected to one end of the hori-zontal portion.ion. An itom or molecule which has feweror more electrons than normal. A positiveion is one which has lost electrons, and anesative ion is one which has acquiredmo-r'e lectrons than normal.ionization. The breaking up of a gas atominto two parts, a free electron and a posi-tively charged ion. This process corre-snon-dso the

"break-down" of an insulator.Ionization makes a gaseous ube more con-ductive than an equivalent vacuum tube-IR drop. A technical expression sometimesused to designate the volt-age-clrop de-veloped across a resistance bv the flow orcurrint through the resistance.iron-core coil. A coil having an iron -corecenter. The iron is usually- in-the formof laminations, but it n'lay also be pulver-ized iron mixed with a binding material'iron-core transformer. A transformer in- iufti.ttl-" makes up part or all of the qathfor maEnetic lines of force travellngthrouEh the translormer windings.Isolantit-e. A high-quality insulating ma-terial used in the construction and mount-ine of radio parts, particularly- thoseemployed in ultra-high frequency circuits'

Jis inserted, thereby giving automaticswitching action.jamming. Intentional transmitting-of radio' *"n". ' in such a way as to interfere withreception of signals from another station'jumpei. A wire used. o connect two pointstogether temPoranlY.

Eas supposed o exist' in the region be-Lu""n 50 and 400 miles above the surfaceof the earth. It reflects radio waves backto earth under certain conditions, making

INTERCOMMUNICATIONSYSTEMSintercommunication system. An amplifiersvstem which provides two-way commllnl-cation between two or more rooms ln att"itaitte. Each station in the system con-fuin= u"-i.tophone and loud-speal


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circuit for transmis-sion of code signals.

l i gh tn ing ar res te r . A

kilocycle. One th6usand cycles but commonlv. .interpret_ed as 1,000 cycles per ;;;;4.- "ki lowatt. One thousand .ivatts,-t(rnscope. A cathode ray tube developedbvthe . Radio Corporatio-n of n*e"-ic'a _aniused n television receivers or the purposeof .teproducing on a screen the sce"i-oiigl_nally televised,Kirclrofrls Current Law. A fundamental elec_trical law which states that the .u* of al tthe currents fl_owing o a point-in-;-;i,;;iimust be equal to the sum of al l the cur___-rentslorvingaway from that point, - -- '-Kirchofr 's - 'ol tage- Law. A iundamentaletectrlcal law which states that the sumof all the voltage sources acting in a c; :L. The letter commonly used on circuit dia_grams and in formrilas 6 a;;i;;;"-;inductance or coil.laminate-d. A_ type of construction widelvused lor the cores of iron core trans'_formers, choke coils, etectromaenetJ. ;;_tors.and,ge.nerators. It involvet bui ldineup. rhe -desrred shape of core with thi istrrps of .a.magnetic material such as softlron or srlrconsteel.lapel m-icrophone.A small microphonewhichcan be attached to a Iapel "; p";k;d;;means of a cl ip.layo"ut. A diagrain indicating the placement_ or parts on a panel or chassis.lead-in.-A wire which serves o connect hesignal.pick-up portion of "" uni"nna-rvrlrem.wlth the antenna terminal of a radioreceiver.lead-in,insulpt-o1.. porcelain tube insertedrn a hote drl l led through an outer wall orw-indos'frameof a houie. t tre teaa_inwiie. o.f he antenna s run through this tuie.- '-leakage. Undesirable now ofc-u".ent itiJo"f,or over the surface of an insulatinE m?lterial. This term is also used to aeicrlfemagnetic flux which wanders otr into space- without doing useful work.leakage [ux. f a_t p-ortion of the total mapr_nerrc flux whlch does not link all of th'eturns of wire in a coil or transformer ani- is consequentlywasted.leakage resistance. The resistanceof a pathtaken by leakagecurrents. fnu.,1he t[ i i ._age resrstanceof a condenser s the nor_mally high -resi:tance r,vhich it "tr;,.r;the flow of the direct current.

. possible long-distance reception.key. A lever-type switchdesignedor idpid open-ing and closinE of ap.letecircuit must be equal to the sum of al l. the voltage drops in tliat same circ;it:- ""knrte swltch. A switch in which one or moreflat metal-blades,each pivoted i l ;";;;.serve as the moving paits. The blades-ailusually..of copperJ when the ;;iii-l;croseo, hey make contact with flat ir in_prng sprrng cl ips and complete he cir:cuit.

/Af f i G @ r &NU ru]ErF r-:' NEflII' {reF Y- =ry EryrypEs F RADrfiioBs -kno_b. A round, tlha.pe.d*i r"""tffi iil?t "1"",or"tljilil ;'.ilLy,?TJfy"lt*#;','",,1:ates the deEree_"{iilf""#J;tf"i,"?r',i",:S':""k'3i,rciL line cord. A two-wire cable terminating in aiy-o--p"olg plug, use4 to connect u-"uaio;,T"'Jiili;l"i'';,1i1fiixt'.,."1'\:j;,S,wire used or the purp.osef ""ar-"i";'ti"l ine voltage o th6_.se'"e c niil;a"'nir",ili""";i tiil if *:"',i.'1'.'i";#,lfi:'::Ji,lfl:,f,-:$:1ilxf;"f,'#f, i,lwhich.might otherwise-"n1"" tt" receiverrrom the_power l ine. I t contains one or_- more choke coils and condense".. - "-lines of force. _Imaginary lines u."d fo" .orr_venl.encen designating directions n which,,_ r""tf.t. or magnetic forces act in space.tlne v'oltage. The voltage existing at a walloutlet or _other terminals of a-pow; it""ili,'"#,J\jll,,XT$*.:*,.,?li ,iiSvolrs, but may vary at times as much asnve volts above and below thesc l imits.load. .That part or c-ombination ipu.*Jnt"whrc_h ower is fed to accomplish a desiredresult.'"?i*,tti,',fntfn1'.i.f"ffi;f"Jfilll*liTJbeen in communication; -;;;i;;;';*li;if i:lieli"l"ll;fi Lllx,l"","rtli:ff3l i,?.#"#:ff ::i H *"#'tecord of_ he meter_reaaings ;hl;;"";;requir,e{ by law to . be take-n "t";;;j;;intervals in,.a broadcast transmitter- aitl,

rn.cerla-lnother types of transmitters.rogglng. fl takinE a record of thc exact dialsetting at whiih a rarormaking-a*,i.t""t',:"::?H"j"'rt:;:t""'r"r""0,:essential data in connection -w-l;t ;;d;;equipment.lok ta l . tube . A smal l_s ize lass r .ad io ubrllying, a ,special base construction wir'iitrlocks the tube firmlv.p""iuis-p"Jn" itlTir.'.1"'f5r:Hii:t3il3re used hiefly n midgetu."._a.".J."iiIii

protective device usedto sidetrack. directly togrouno a dlscharEe oflightning .lvhichstrikes-. a.radio_receivingor transmitting antenna.l imiter. In an F.M. receiver, the sectionwhich removes amplitude variations fronrthe F.M. signal at the output of the I.F.amplif ier, thereby l imiting intelferingn o l s e $ .t 7


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and in auto radios.long waves. Wave lengths longer than thelongest broadcast band wave length of545 meters. Long waves correspond tofrequencies between about 20 kilocyclesand 550 kilocycles.loop antenna. An antenna consisting of oneor llore complete turns of wire. It may bebuilt into a radio receiver cabinet orseparately mounted, and is usually tuned toreasonanceby a variable condenser. Loopantennas are used extensively in radiodirection-fi nding apparatus.losses. Energy which is dissipated before itaccomplishes useful work.loudspealker. A device for converting auiliofrequency signals into sound waves.louver. A type of loudspeaker grille con-M

l\I. A letter sometimes used to indicate thata particular resistance value is to be mul-tiplied by 1,000. Thus, 50M would mean50,000ohms.ma. Milliampere,magnet. A piece of iron or steel which hasthe property of attracting other pieces ofnlagnetic material such as iron, and hasthe property of attracting or repellingother masnets.magnet wire. Insulated copper wire in sizescommonly used for winding coils used inelectro-magnetic devices such as trans-formers, choke coils and relays.magnetic circuit, A complete path for mag-netic lines of force. It always includes thepermanent magnet or electromagnet whichis producing the magnetic lines of force.magnetic field. A region in space surround-ing a magnet or a conductor through whiehcurrent is flowing.magnetic lines of force. Imaginary lines usedfor convenience o designate the directionsin which magnetic forces are actingthroughout the magnetic field associatedwith a permanent magnet, electromagnetor current-carrying conductor.magnet i c oudspeaker . Aloudspeaker consisting es-sentially of a permanentmagnet, a pivoted arma-ture which is mechanicallconnected to the dia-phragm or cone, and acoil which is connected tothe output stage of a radioreceiver or other appa-ratus. Interaction between

struction in which sloping slats or equiva-lent parts of a molded plastic cabinet hidethe loudspeaker yet allow sound waves toemerge unhindered. Also spelled louvre.low-frequency padder. In a superheterodynereceiver, a semi-adjustable condenserwhich is placed in series with the oscillatortuning circuit to control the calibration ofthe circuit at the low-frequency end of thetuning range.low-loss construction. A type of radio partconstruction involving the use of insulatingmaterials which maintain their insulatingcharacteristics at high radio frequencies.lug. A small strip of metal placed on a ter-minal-screw or riveted to an insulatingmaterial to provide a convenient meansfor making a soldered wire connection.lines of force acting in a magnetic circuit.man-made static. High-frequency noise sig-nals which are produced by sparking inelectrical apparatus or power lines andpicked up by radio receivers,with the resultthat buzzing and crashing sounds a.reheard along with a desired radio program.rnanual tuning. Tuning a radio receiver toa desired station by rotating the tuningcontrol knob by hand.rnatching. Connecting two circuits br partstogether with a coupling device in such away that the impedance of either circuitwil l be equal to the impedanceexisting be-tween the coupling terminals to whichthat circuit is connected.maximum undistorted output. The maximumaudio power output which a radio receiveror audio amplifier will deliver withouthaving more than 70/o total harmonic dis-tortion. Tests have shown that this amountof distortion is not ordinarily noticeableor objectionable.MAYDAY. The international distress callfor radiotelephone communication. It isderived from the French pronunciation of"M'aidez," meaning t'Help-me.t 'mc. Megacycle.

rneg. Megohm.megacycle._One million cycles per second,megohm. One million ohms.mercury. A heavy, silvery-colored metalwhich is l iquid at ordinary room tempera-tures. When heated, it Eives off a rianorwhich is highly conductivewhen ionized.mercury vapor rectifier tube. A rectifier tubecontaining_a small amount of mercury.When the filament or heater-type cathodeis heated, mercury vapor is prb'duced,andthe resultlng' ionization of the mercurvvapor molecules gives a much hiEher nlatLcurrent than u'ould be obtained in anequivalent vacuum type rectifier tube.metallized resistor.A resistor madeby depositing athin film of high-resistancemetalon

the permanent maEnetic field and that de-veloied in the armature by the coil resultsin movement of the armature and pro-duction of sound waves by the diaphragm.magnetic pick-up. A phonograph pick-upconsisting of a permanent magnet, one ortwo coils, an iron armature and a corestructure so arranged that movement ofthe phonograph needle in the recordgroove varies the amount of magneticflux passing through the coils, thereby in-ducing audio frequency voltages in thecoils.magnetic flux. Total number of mag:netict 8

the surface of a tube or rod made of glassof other insulating material. Leads are at -tached to opposite ends of the unit.


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metal-type tube. _A vacrum ol gaseous ubehavine a metal envelope or housing withelectrodeconnectionsbeing made throughglass beads used into the metal envelope.

METAL TUDECourtesY 1l.C.A. tr[1g. Co., Inc'meter. The unit of length in the metricsystem; one meter is equal to 3.28 feet.An instrument used for making electricalmeasurements. Examples: voltmeterr am-meter, milliammeter, ohmmeter.mfd. Microfarad.mh. Millihenry.mho. A unib oi conductivity. The reciprocalof ohrn.

of flexible diaphragm which moves in ac-cordancewith sound wave variations. Thismovement, in turn, generates a minutevoltage which is fed to the input of anamplifier where it is amplified many times.There are several types of microphonesavailable, but they all operate on the aboveprinciple. Carbon Microphone. A micro-phone- in which loosely packed carbongranules complete the electrical circuitbetween two terminals. The resistance ofthis circuit varies in accordancewith varia-tions in the pressure exerted on the gran-ules by the sound-actuated diaphragm. Ina single-button carbon miocrophone, thegranules are on only one side of the dia-phragm. In a double-button carbon micro-phone the granules are on both sides ofthe diaphragm, giving a push-pull actionwhich greatly increases the resistancechange produced by a given diaphragmmovement. Condenser Microphone. A mi-crophone in which the diaphragm serves asone plate of acondenser.Soundwavesmovethe diaphragm in and out, causing thecapacity of the microphone and the currentthrough it to vary in accordance with thesound waves. Contact Microphone. A mi-crophone designed to pick up mechanicalvibrations directly and convert them intoelectrical impulses. It is used chiefly withstring, wind, and percussion musical in-struments, and is simply strapped orclamped to the housing of the instrument.

CAREONica. A transparent flaky mineral whichsoli ts readilv into thin sheetsand has ex-ci l lent insulating and heat-resisting qual-ities. It is used extensively to separatethe nlates of condensers, o insulate elec-trode elements of vacuum tubes, and formanv other insulating purposes in radio.mica cbndensers.Acondenserwhichemployssheets of mica as the dielectric materialbetween plates. tffilB,ffiltlti|mErilxtuutd@1ffi

M I C A C O N D E N S E R Smicro. A prefix meaning one millionth.rr icroamp-ere. One mil l ionth of an ampere.r ,icrofarad. A unit of capacity equal to onemil l ionth of a farad. The microfarad is

the capacity unit most commonly us-ed nradio work. It is abbreviated as mfd.micromho. One millionth of a mho. Used tomeasure tube transconductance'micro-rnicrofarad. A unit of capacity equalto one millionth of a microfarad, and ab-breviated as mmfd.microphone. A device which converts sounds'aves nto correspondingaudio frequencyelectrical energy. I t contains some form

ffiU DYNAM,.ffi,*.",:*rystal illicrophone. A microphone de-pending upon the piezoelectic effect ofRochelle salt crystals to transform the me-chanical stress produced by sound wavesinto electrical output. In general, crystalmikes are non-directional and have goodfrequency response. Dynamic Microphone.A microphone in which the diaphragmrnoves a voice coil back and forth in aconstant magnetic field, causing audio cur-rents to be induced in the coil. A srnalldynamic loudspeaker is often made to servealso as a dynahic microphone, particularlyin two-way intercommunication systems.Yelocity or Ribbon Microphone. A micro-phone in which a thin light-weight rib-bon or duralumin alloy serves as thet 9


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diaphragm. This ribbon is mounted in apowerful fixed magnetic field. Audio fre-quency voltages are induced in the ribbonwhen it is moved back and forth throughthe magnetic field by sound waves.microphone pre-amplifier. An audio ampli-fier which ampiifies the output of a micro-phone sufficienUy so that the audio signalmay be sent over a transmission line tothe main amplifier. Sometimes, particu-larly with condenser microphones, thismicrophone amplifier is mounted right onthe micronhone stand or in the microphonehousinE tself.microphoie button. A button-shaped con-tainer filled with carbon particles. Whenattached to the diaphragm of a microphone,the resistance between the terminals of thebutton varies in accordance with move-ments of the diaphragm.microphone stand. A table or floor-typestand used to support a microphone in adesired position.microphone transformer. The iron-core a.f.transformer which couples the microphoneto a microphone amplifier, to a transmis-sion line, or to the input circuit of the mainaudio amplifier.microphonic. A condition in which mechani-cal movement of some radio part otherthan a microphone causes correspondingvariations in circuit current. A radio tubeis microphonic if a pinging sound is heardin the loudspeaker when the side of thetube is tapped with a finger; the tappingis then setting the internal elements intovibration. If sound waves from the loud-speaker are producing this vibration oftube elements. the sound will be sustainedas a howl.mike. A microphone.milli. A prefix meaning one thousandth.milliammeter. A measuring instrument whichmeasures current flow in milliamperes.milliampere. A unit of current equal to onethousandth of an ampere.millihenry. A unit of inductance equal toone thousandth of a henry.millimeter. A metric unit of length equal toone thousandth of a meter. One millimeteris apptoximately equal to one twenty-fifthof an inch.millivolt. A unit of voltage equal to onethousandth of a volt.mixer. A control which permits combiningthe output signals of two or more micro-phones or other a.f. signal sources in anydesired proportion before these signals arefed to the input of the main a.f. amplifier.Also, the stage in a superheterodyne re-ceiver in which the incoming modulated r.f.signals are mixed with the local oscillatorsignals to produce the i.f. signal.mm. Millimeter.modulated amplifier. The r.f. stase in amovable location such as on an automobile,fire truck, railway train, ship or airplane.modulated amplifier. The r.f. stage in atransmitter at which the intelligence sig-nal is made to modulate the r.f. carriei'signal.modulated wav: A radio wave which varies20

either in frequency (frequency modula-tion) or in amplitude (amplitude modula-tion) in accordancewith the wave form ofthe intelligence signal being transmitted.modulation. The process of varying the fre-quency or the amplitude of an r.f. carriersignal in accordance with the wave formof the intelligence signal being trans-mitted.modulator. The final audio stage in a radiotransmitter. It feeds the intelligence sig-nal into the modulated amplifier stage,where the signal is made to modulate ther.f. carrier signal,molecule. The group of atoms which consti-tutes the smallest particles in which a com-pound or material can exist separately.monkey chatter. Garbled speech or musicheard along rvith a desired program. Thistype of interference occurs when the sidefrequencies of an adjacent-channel stationbeat with the desired station signal,monoscope. A special type of cathode raytube which produces television picture sig-nals corresponding to the design or picturervhich has 6een pr-intedon itsicreeri. Thistube is used in television picture signalgenerators to provide a satisfactory signalsource for television receiver test purposesduring those times when no television sta-tion is on the air.ilIorse Code. A system of dot and dash sig-nals used in the transmission of messagesby radio or wire telegraphy. The Intbr-national Morse Code (also called the Con-tinental Code) is used universally for radiotelegraphy, while the Americln MorseCode is used onlv for wire teleqraphv.mosaic.The light-sensitive plate in an icono-s-cope.The scenebeing transmitted is pro-.iectedupon this plate, and is then scannedby the electron beam to produce the oic-ture signal output of the television cam6ra,motor. A machine which converts electricalenergy into mechanical energy.motorboating. Regeneration occurring ataudio frequencies in a radio receiver oraudio amplifier, resulting in put-put-putsounds resembling those made by a motor-boat.motor-generator. An electric motor directlyconnected to one or more generators forthe purpose of converting a power linevoltage to other desired voltages or fre-quencres.mu. Amplification factor.multimeter. A testinstrument hav-ing provisions fo rmeasuring volt-a g e s a n d c u r -rents, as well asresistance. It us-ually consists ofone or sometimestwo meters pro-vided with thenecessary num-ber of scales, anda range-selectins w i t c h w h i cplaees a meter inthe correct cir-


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cuit for a particular measurement' Alsoi."o*" as a- multitester, multiple-purposetester or volt-ohm-milliammeter' Nneedle. That part-of a phonograph pick-upwhich converts the variations in the recordgrooves into mechanical movements which

ire in turn converted into audio frequencyiignals by the.pick-up element. The needlemust be carefully shaped to follow fait}-fully the high-frequency variations in thegrooves without causing excesslve recordwear.necative. A term used to describea terminalihich hu" more electrons than normal.Electrons flow out ofthe negative terminalof a voltage source.neeitin" biis. The use of a voltage whichirakes the control grid of a radio tubeneEative with respect to the cathode.negalive feedback. Degeneration, causing aieduction in signal strength.negative modulation. In television,a method- 5f t"utt.tttission in which a decrease inicene illumination causes an increase inthe radiated power of the transmitter.neon. A pure las sometimes used in elec-- tronic tubes.-It produces a characteristicred EIow when ionized.neon g"low amp. A n-eon-filledgaseous-tubehavlng a glais enve

a dictionary of radio terms

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