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Electronics Systems and Technologies Engr. Jaime P. Licuanan, CCNA

CHAPTER 1 :Introduction to Electronic Communications

the transmission, reception and processing of information between two or more locations using electronic circuits electronic

communications

signals that are time-varying voltages or currents that are continuously changing, such as cosine and sine waves. It contains an infinite number of values

analog signals

signals that are voltages or currents that change in discrete steps or levels

digital signals

he invented the first workable telegraph Samuel Finley Breese Morse (1837)

it is used to transfer information in the form of dots, dashes and spaces between a simple transmitter and receiver using a transmission line consisting of a length of metallic wire

electromagnetic induction

they were the first to successfully transfer human conversation over a crude metallic-wire communication system using a device they called telephone

Alexander Graham BellThomas A. Watson

a logarithmic unit that can be used to measure ratios of virtually anything

decibel (dB)

a transmission-measuring unit used to express relative gains and losses of electronic devices and for describing relationships between signals and noise

decibel

another name for power loss attenuation a collection of one or more electronic devices or circuits that

converts the original source information to a form more suitable for transmission over a particular transmission medium transmitter

it provides a means of transporting signals between a transmitter and a receiver and can be as simple as a pair of copper wires

transmission medium or communications channel

any unwanted electrical signals that interfere with the information signal

system noise

a collection of electronic devices and circuits that accepts the transmitted signals from the transmission medium and then converts those signals back to their original form

receiver

higher-frequency analog signal carrier

the process of changing one or more properties of the analog carrier in proportion with the information signal

modulation

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a system in which energy is transmitted and received in analog form, both the information and the carrier are analog signals

Analog communication system

it covers a broad range of communication techniques including digital and digital radio

Digital communication system

a true digital system where digital pulses are transferred between two or more points in communication system digital transmission

the transmittal of digitally modulated analog carriers between two or more points in communication system digital radio

the information signal is analog and the amplitude of the carrier is varied proportional to the information signal Amplitude modulation

(AM)

the frequency is varied proportional to the information signal Frequency modulation (FM)

a circuit performing modulation in a transmitter modulator

a carrier that has been acted on by an information signal modulated wave or modulated signal

the reverse process of modulation and converts the modulated carrier back to the original information demodulation

it is often used to refer to a specific band of frequencies allocated a particular service

channel

another name for information signal intelligence signal

the process of converting a frequency or band of frequencies to another location in the total frequency spectrum

frequency translation

it can propagate as a voltage or current along a metallic wire as emitted radio waves through free space or as light waves down an optical fiber

electromagnetic energy

simply the number of times a periodic motion such as sine wave of voltage or current occurs in a given period of time frequency

an international agency in control of allocating frequencies and services with the overall frequency spectrum

International Telecommunications Union (UTI)

signals in the 30-Hz to 300-Hz range and include ac power distribution signals (60Hz) and low frequency telemetry signals Extremely low

frequencies

signals in the 300-Hz to 3000-Hz range and include frequencies generally associated with human speech, standard telephone channels

Voice frequencies

signals in the 3-kHz to 30-kHz range which include the upper end of the human hearing range, specialized government and Very low frequencies

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military system (submarine communications)

signals in the 30-kHz to 300-kHz range and used primarily for marine and aeronautical navigation Low frequencies

signals in the 300-kHz to 3-MHz range and are used primarily for commercial AM radio broadcasting (535 kHz to 1605 kHz) Medium frequency

signals in the 3-MHz to 30-MHz range and are used for two-way radio communications, Voice of America and Radio Free Europe broadcast, amateur radio and citizens band (CB) radio

High frequencies

signals in the 30-MHZ to 300-MHz and are used for mobile radio, marine, and aeronautical communications, commercial FM broadcasting (88 MHz to 108 MHz), and commercial television broadcasting of channels 2 to 13 (54 MHz to 216 MHz)

Very high frequencies

signals in the 300-MHz to 3-GHz range and are used by commercial television broadcasting of channels 14 to 83, land mobile communication services, cellular telephones, certain radar and navigation systems, and microwave and satellite radio systems

Ultrahigh frequencies

signal in the 3-GHz to 30-GHz range used for microwave and satellite radio communication system Superhigh frequencies

signals in the 30-GHz to 300-GHz range and seldom used for radio communication system

Extremely high frequencies

signal in the 0.3-THz to 300-THz range. It refers to electromagnetic radiation generally

associated with heat

Infrared

the length that one cycle of an electromagnetic wave occupies in space. It is inversely proportional to the frequency of the wave and directly proportional to the frequency of the wave and directly proportional to the velocity of propagation

wavelength

speed of light 3 x 108 m/s the two most significant limitations on the performance of a

communication system noise bandwidth

simply the difference between the highest and lowest frequencies in the information

bandwidth of an information signal

the difference between the highest and lowest frequencies that the channel will allow to pass through

bandwidth of a communication channel

a highly theoretical study of the efficient use of bandwidth to propagate information through electronic communications system

Information theory

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a measure of how much information can be propagated through a communications system and is a function of bandwidth and transmission time

Information capacity

simply the number of bits transmitted during one second and is expressed in bit per second Bit rate

any undesirable electrical energy that falls within the passband signal

Electrical noise

implies a relationship between the signal and the noise. Exist only when a signal is present

correlated

noise present all the time whether there is signal or not uncorrelated

noise that is generated outside the device or circuit external noise

naturally occurring electrical disturbances that originate within Earth’s surface like lightning

Atmospheric noise

another name for atmospheric noise Static electricity

frequency of atmospheric noise 30 MHz

consists of electrical signal that originate from outside Earth’s atmosphere

Extraterrestrial noise

another name for extraterrestrial noise Deep-space noise

continuously distributed throughout the galaxies Cosmic noise

another name for cosmic noise Black-body noise

simply noise that is produced by mankind Man-made noise

another name for man-made noise Industrial noise

electrical interference generated within a device or circuit internal noise

caused by random arrival of carriers at the output element of an electronic device such as diode, field effect transistor or bipolar transistor

Shot noise

any modification to a stream of carriers as they pass from the input to the output of a device produces an irregular random variation

Transit-time noise

the rapid and random movement of electrons within a conductor due to thermal agitation

Thermal noise

another names for thermal noise: white noise Brownian noise Johnson noise

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occurs when unwanted harmonics of a signal are produced through nonlinear amplification

Harmonic distortion

integer multiples of the original signal Harmonics

another name for harmonic distortion Amplitude distortion

the generation of unwanted sum and difference frequencies produced when two or more signals mix in a nonlinear device Intermodulation

distortion

characterized by high-amplitude peaks of short duration in the total noise spectrum

Impulse noise

a form of external noise meaning to disturb or detract from Interference

when information signals from one source produce frequencies that fall outside their allocated bandwidth and interfere with information signals from another source

Electrical interference

the ratio of the signal power level to the noise power level Signal-to-noise power ratio

CHAPTER 2: Signal Analysis and Mixing

the only two levels possible in a digital signal

binary signal

four-level signals quaternary digital signal

the voltage- or current-time variations that can be represented by a series of sine or cosine waves

Electrical signals

a waveform which repeats at a uniform rate Periodic

a description of a signal with respect to time Time domain

a time-domain instrument Oscilloscope

an amplitude-versus-time representation of the signal

Signal waveform

a description of a signal with respect to its frequency

Frequency-domain representation

a frequency-domain instrument Spectrum analyzer

any repetitive waveform that is comprised of more than one harmonically related sine or cosine wave

Sinusoidal wave

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any periodic waveform that is not a sinusoid such as square waves, rectangular waves and triangular waves

Complex wave

a French physicist and mathematician who used a mathematical series to analyze a complex periodic wave

Baron Jean Fourier

a mathematical tool that allows us to move back and forth between time and frequency domains. It is used in signal analysis to represent the sinusoidal components of non-sinusoidal periodic waveforms

Fourier analysis

it describes the symmetry of a waveform in the time domain, that is, its relative position with respect to the horizontal (time) and vertical (amplitude) axes

Wave symmetry

a periodic voltage waveform in symmetric about vertical axis that have axes, or mirror, symmetry

Even symmetry

a periodic voltage waveform that said to have point, or skew, symmetry

Odd symmetry

a periodic voltage waveform such that the waveform for the first half-cycle repeats itself except with the opposite sign for the second half cycle

Half-wave symmetry

a waveform consists of all the frequencies contained in the waveform and their respective amplitudes plotted in the frequency domain

Frequency spectrum

range of frequencies contained in the spectrum the difference between the highest and lowest

frequencies contained in the information the difference between the highest and lowest

frequencies that the channel will allow to pass through

Bandwidth

the rate at which energy is dissipated, delivered, or used and is a function of the square of the voltage or current

Electrical power

a time-domain signal is sampled at discrete times Discrete Fourier transform

the computing time is proportional to n log 2n rather that n2

Fast Fourier series

it reduces the information capacity of the system Bandlimiting the process of combining two or more signals and is

an essential process in electronic communicationsMixing

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two ways in which signals can be combined or mixed:

linearly nonlinearly

it occurs when two or more signals combine in a linear device, such as passive network or a small-signal amplifier

Linear summing (linear mixing)

occurs when two or more signals are combined in a nonlinear device such as a diode or large-signal amplifier

Nolinear mixing

undesired harmonics Harmonic distortion

desired harmonics Frequency multiplication

CHAPTER 3 : Oscillators, Phase-Locked Loops,and Frequency Synthesizers

to fluctuate between two states or conditions, to vibrate or to change

Oscillate

a device that produces oscillations Oscillator

an amplifier with a feedback loop (i.e., a path to propagate from the output back to input)

Feedback oscillators

four requirements for a feedback oscillator: amplification positive feedback frequency-

determining components

power source

an untuned oscillator RC phase shift oscillator that uses both positive and negative feedback

Wien-bridge oscillator

oscillator circuits that utilize tuned LC tank circuits for the frequency-determining components

LC oscillators

the ability of an oscillator to remain at a fixed frequency and is of primary importance in communication systems

Frequency stability

feedback oscillator circuits in which the LC tank circuit is replaced with a crystal for the frequency-determining component

Crystal oscillators

the study of the form, structure, properties, and classifications of crystals. It deals with lattices, bonding and the behavior of slices of crystal material that have been cut at various angles with respect to the crystal’s axes

Crystallography

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it occurs when oscillating mechanical stresses applied across a crystal lattice structure generate electrical oscillations and vice versa

Piezoelectric effect

another name for mechanical vibrations Bulk Acoustic Waves (BAWs)

it is consist of a crystal-controlled oscillator and a voltage-variable component such as varactor diode

Crystal oscillator module

it is often used when describing varactor diode fabrication

Graded junction

CHAPTER 4 : Amplitude Modulation Transmission

the process of impressing low-frequency information signal onto a high-frequency

Modulation

the reverse process where the received signals are transformed back to their original form

Demodulation

the process of changing the amplitude of a relatively high frequency carrier signal in proportion with the instantaneous value of the modulating signal

Amplitude Modulation (AM)

frequencies that are high enough to be efficiently radiated by an antenna and propagated through free space

Radio frequency

the most commonly used amplitude modulation AM double side-band full carrier (AM DSBFC)

a term used to describe the amount of amplitude change present in an AM waveform

Coefficient of modulation

gives the percentage change in the amplitude of the output wave when the carrier is acted on by a modulating signal

Percent modulation

it use a unique arrangement of transistors and FETs to perform signal multiplication, which is a characteristic that makes them ideally suited for generating AM waveforms

Linear integrated-circuit function generators

typically a sensitive class A linear voltage amplifier with a high input impedance

Preamplifier

a low-gain, high-input impedance linear amplifier used to isolate the oscillator from the high-power amplifiers

Buffer amplifier

it is sometimes called upward or downward

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modulation and has absolutely nothing to do with the frequency of the carrier. A form of amplitude distortion introduced when positive and negative alternations in the AM modulated signal are not equal

Carrier shift

are complex waveforms comprised of two or more frequencies

Nonsinusoidal signals

are complex waves made up of two or more harmonically related sine waves and include square, rectangular and triangular waves

Complex repetitive

a form of amplitude modulation where signals from two separate information sources modulate the same carrier frequency at the same time without interfering with each other

Quadrature amplitude modulation

CHAPTER 5 : Amplitude Modulation Reception

several parameters commonly used to evaluate the ability of a receiver to successfully demodulate a radio signal

selectivity bandwidth sensitivity dynamic range fidelity insertion loss noise temperature

a receiver parameter that is used to measure the ability of the receiver to accept a given band of frequencies and reject all others

Selectivity

the noise reduction ratio achieved by reducing the bandwidth

Bandwidth Improvement (BI)

the corresponding reduction in the noise figure to the reduction in bandwidth

Noise Figure Improvement

the minimum RF signal level that can be detected at the input to the receiver and still produce a usable demodulated information signal

Sensitivity

another name for receiver sensitivity Threshold

the difference in decibels between the minimum input level necessary to discern a signal and the input level that will overdrive the receiver and produce distortion

Dynamic range

the output power when the RF amplifier response is 1 dB less than the ideal linear-gain response

1-dB compression point

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a measure of the ability of a communication system to produce at the output of the receiver, an exact replica of the original source information

Fidelity

three forms of distortion that can deteriorate the fidelity of a communication system:

amplitude frequency phase

the predominant cause of phase distortion Filtering

the total phase shift encountered by a signal and can generally be tolerated as long as all frequencies undergo the same amount of phase delay

Absolute phase shift

it occurs when different frequencies undergo different phase shifts and may have a detrimental effect on a complex waveform

Differential phase shift

it occurs when the amplitude-versus-frequency characteristics of a signal at the output of a receiver differ from those of the original information signal

Amplitude distortion

it occurs when frequencies are present in a received signal that were not present in the original source information

Frequency distortion

a parameter associated with the frequencies that fall within the passband of a filter and is generally defined as the ratio of the power transferred to a load with a filter in the circuit to the power transferred to a load without the filter

Insertion Loss (IL)

a hypothetical value that cannot be directly measured. An indication of the reduction in the signal-to-noise as a signal propagates through a receiver

Equivalent Noise Temperature (Te)

two basic types of radio receivers: coherent (synchronous) noncoherent (asynchronous)

a type of receiver wherein the frequency generated in the receiver and used for demodulation are synchronized to oscillator frequencies generated in the transmitter

Coherent

a type of receiver where either no frequencies are generated in the receiver or the frequencies used for demodulation are completely independent from the transmitter’s carrier frequency

Noncoherent

another name for noncoherent detection because the information is recovered from the received waveform by detecting the shape of the modulated

Envelope detection

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envelope

one of the earliest types of AM receivers and probably the simplest designed radio receiver available

Tuned Radio-frequency (TRF)

it means to mix two frequencies together in a nonlinear device or to translate one frequency to another using nonlinear mixing

Heterodyne

five sections of the superheterodyne receiver:

RF section Mixer/converter section IF section Audio detector section Audio amplifier section

a broad-tuned bandpass filter with an adjustable center frequency that is tune to the desired carrier frequency. It reduce the noise bandwidth of the receiver

Preselector

it determines the sensitivity of the receiver RF amplifier

its purpose is to convert the IF signals back to the original source

Detector

the ability of the local oscillator in a receiver to oscillate either above or below the selected radio frequency carrier by an amount equal to the intermediate frequency throughout the entire radio frequency band

Tracking

the difference between the actual local oscillator frequency and the desired frequency

Tracking error

any frequency other than the selected radio frequency carrier that if allowed to enter a receiver and mix with the local oscillator will produce a cross-product frequency that is equal to the intermediate frequency

Image frequency

a numerical measure of the ability of a preselector to reject the image frequency

Image-frequency rejection ratio

it occurs when a receiver picks up the same station at two nearby points on the receiver tuning dial

Double spotting

its purpose is to down-convert the incoming radio frequencies to intermediate frequencies

Mixer / converter

the most common technique used for coupling IF amplifiers where the voltage that is applied to the primary windings of a transformer is transferred to the secondary windings

Inductive or transformer coupling

the ability of a coil to induce a voltage within its own windings

Self-inductance

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the ability of one coil to induce a voltage in another coil

Mutual inductance

the ratio of the secondary flux to the primary flux Coefficient of coupling

the transfer of flux from the primary to the secondary windings

Flux linkage

a circuit that compensates for minor variations in the received signal level where it automatically increases the receiver gain weak RF input levels and automatically decreases the receiver gain when a strong RF signal is received

Automatic Gain Control (AGC)

when the receiver becomes less sensitive Automatic desensing

a circuit that has the purpose to quiet a receiver in the absence of a received signal. It keeps the audio section of the receiver turned off or muted in the absence of a received signal

Squelch circuit

used for removing sporadic, high amplitude noise transients of short duration such as impulse noise

Diode limiters or clippers

another circuit option commonly used for reducing the effects of high amplitude noise pulses where it detects the occurrence of a high-amplitude, short duration noise spike then mutes the receiver by shutting off a portion of the receiver for the duration of the pulse

Blanking circuit

the ratio of the demodulated signal level at the output of the receiver to the RF signal level at the input to the receiver

Net Receiver Gain

samples of receiver losses: preselector loss mixer loss detector loss

it includes all the gains and losses incurred by a signal as it propagates from the transmitter output stage to the output of the detector in the receiver and includes antenna gain and transmission line and propagation losses

System gain

the adjustment for the center frequency of the preselector and the adjustment for the local oscillator

Gang tuned

it offers higher gain and less noise than conventional cascaded amplifiers

Cascoded amplifier

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CHAPTER 6 Single-Sideband Communications System

a form of amplitude modulation in which the carrier is transmitted at full power but only one of the sidebands is transmitted. It requires only half as much bandwidth as conventional double sideband AM

AM Single-sideband Full Carrier (SSBFC)

a form of amplitude modulation in which the carrier is totally suppressed and one of the sidebands removed and considerably less transmitted power

AM Single-sideband Suppressed Carrier (SSBSC)

a form of amplitude modulation in which one sideband is totally removed and the carrier voltage is reduced to approximately 10% of its unmodulated amplitude

AM Single Side-band Reduced Carrier (SSBRC)

a form of amplitude modulation in which a single carrier frequency is independently modulated by two different modulating signals

AM Independent Sideband (ISB)

a form of amplitude modulation in which the carrier and one complete sideband are transmitted but only part of the second sideband is transmitted

AM Vestigial Sideband (VSB)

the rms power developed at the crest of the modulation envelope when the modulating-signal frequency components are at their maximum amplitudes

Peak envelope power (PEP)

advantages of single-sideband transmission: power conservation bandwidth conservation selective fading noise reduction

disadvantages of single-sideband transmission: complex receivers tuning difficulties

a circuit that produces a double-sideband suppressed-carrier signal

Balanced Modulator

another name for balanced modulator Balanced Lattice Modulator

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a small carrier component always present in the output signal

Carrier Leak

the typical amount of carrier suppression between 40 dB and 60 Db

three transmitter configurations used for single-sideband generation:

phase-shift method filter method third method

it is made from lead zirconate-titanate which exhibits the piezoelectric effect

Ceramic filters

a mechanically resonant transducer that when it receives electrical energy, it converts to mechanical vibrations and then converts the vibrations back to electrical energy at its output

Mechanical filter

four elements that comprise a mechanical filter: input transducer series of mechanical

resonant metal disks coupling rod output transducer

filters that use acoustic energy rather than electromechanical energy to provide excellent performance for precise bandpass filtering

Surface Acoustic Wave (SAW) filters

the basic SAW filter Bidirectional

it launches the acoustic wave in only one direction Unidirectional

a narrow band PLL that tracks the pilot carrier in the composite SSBRC receiver signal and uses the recovered carrier to regenerate coherent local oscillator frequencies in the synthesizer

Recovery circuit

a system that provide narrowband voice communications for land-mobile services with nearly the quality achieved with FM systems and do it using less than one-third the bandwidth

Amplitude-compandoring Single-sideband (ACSSB)

a device that performs compression and expansion Compandor(compressor-expander)

process of combining transmissions from more than one source and transmitting them over a common facility, like metallic or optical fiber cable or a radio-frequency channel

Multiplexing

an analog method of combining two or more analog sources that originally occupied the same frequency band in such a manner that the channels do not interfere with each other

Frequency-division Multiplexing (FDM)

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a multiplexing method that uses double-sideband suppressed-carrier transmission to combine two information sources into a single composite waveform that is then transmitted over a common facility without the two channels interfering with each other

Quadrature Multiplexing (QM)

CHAPTER 7 Angle Modulation Transmission

it results whenever the phase angle modulation of a sinusoidal wave is varied with respect to time

Angle modulation

varying the frequency of a constant-amplitude carrier directly proportional to the amplitude of the modulating signal at a rate equal to the frequency of the modulating signal

Direct Frequency Modulation (FM)

varying the phase of a constant-amplitude carrier directly proportional to the amplitude of the modulating signal at a rate equal to the frequency of the modulating signal

Direct Phase Modulation (PM)

the relative angular displacement of the carrier phase in radians in respect to the reference phase

Phase deviation (Δθ)

the relative displacement of the carrier frequency in hertz in respect to its unmodulated value

Frequency deviation (Δf)

four terms with reference to angle-modulation

instantaneous phase deviation

instantaneous phase instantaneous

frequency deviation instantaneous

frequency

the instantaneous change in the phase of the carrier at a given instant of time and indicates how much the phase of the carrier is changing with respect to its reference phase

Instantaneous phase deviation

the precise phase of the carrier at a given instant of time

Instantaneous phase

the instantaneous change in the frequency of the carrier and is defined as the first time derivation of the instantaneous frequency deviation

Instantaneous frequency deviation

the precise frequency of the carrier at a given instant of time and is defined as the first derivative of the instantaneous phase

Instantaneous frequency

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it can be defined as angle modulation in which the instantaneous phase deviation is proportional to the amplitude of the modulating signal voltage and the instantaneous frequency deviation is proportional to the slope or first derivative of the modulating signal

Phase modulation

an angle modulation in which the instantaneous frequency deviation is proportional to the amplitude of the modulating signal and the instantaneous phase deviations is proportional to the integral of the modulating signal voltage

Frequency modulation

the output-versus-input transfer functions for the modulators which give the relationship between what output parameter changes in respect to specified changes in the input signal

Deviation sensitivities

peak phase deviation Modulation index the change in frequency that occurs in the carrier

when it is acted on by a modulating-signal frequencyFrequency deviation

peak-to-peak frequency deviation Carrier swing

the ratio of the frequency deviation actually produced to the maximum frequency deviation allowed by law stated in percent form

Percent Modulation

a circuit in which the carrier is varied in such a way that its instantaneous phase is proportional to the modulating signal

Phase modulator

a single-frequency sinusoid

Unmodulated carrier (rest frequency)

a circuit in which the carrier is varied in such a way that its instantaneous phase is proportional to the integral of the modulating signal

Frequency modulator (frequency deviator)

differentiator followed by an FM modulator PM Modulator

FM demodulator followed by an integrator PM demodulator

integrator followed by a PM modulator FM modulator

PM demodulator followed by a differentiator FM demodulator

rule that approximates the bandwidth necessary to transmit an angle-modulated wave as twice the sum of the peak frequency deviation and the highest modulating-signal frequency, it defines a bandwidth that includes approximately 98% of the total power in the modulated wave

Carson’s rule

the worst-case modulation index and is equal to the maximum peak frequency deviation divided by the Deviation Ratio (DR)

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maximum modulating-signal frequency

the interference produced when the highest side frequencies from one channel are allowed to spill over into adjacent channels

Adjacent Channel Interference

the noise voltage at the output of a PM demodulator is constant with frequency, whereas the noise voltage at the output of an FM demodulator increases linearly with frequency

Noise Triangle

a high-pass filter

Preemphasis Network

a low-pass filter Deemphasis Network

an angle modulation in which the frequency of the carrier is varied directly by the modulating signal

Direct FM

an angle modulation in which the frequency of the carrier is deviated indirectly by the modulating signal

Direct PM

a circuit that compares the frequency of the noncrystal carrier oscillator to a crystal reference oscillator and then produces a correction voltage proportional to the difference between two frequencies

Automatic Frequency Control (AFC)

a purpose to achieve near-crystal stability of the transmit carrier without using a crystal in the carrier oscillator

AFC loop

meaning cancel of the deviation thus removing the modulation from the FM wave

wipe off

transmitters that produce an output waveform in which the phase deviation is directly proportional to the modulating signal therefore the carrier oscillator can be a crystal because the oscillator itself is not a

modulator

Indirect FM transmitters

the low-pass filter that is simply 1/f filter

Predistorter (frequency correction network)

advantages of angle modulation:

noise immunity FM thresholding capture effect power utilization and

efficiency

it allows a receiver to differentiate between two signal received with the same frequency

Capture effect

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CHAPTER 8 : Angle Modulation Reception and FM Stereo

it rejects the image frequency Preselector

it establishes the signal-to-noise ratio and noise figure RF amplifier

down-converts RF to IF Mixer/converter

it provides most of the gain and selectivity of the receiver

IF amplifiers

it removes the information from the modulated wave Detector

it is a frequency-dependent circuits designed to produce an output voltage that is proportional to the instantaneous frequency at its input

FM Demodulators

the most common circuits used for demodulating FM signal

slope detector Foster-Seeley

discriminator ratio detector PLL demodulator quadrature detector

it converts FM to AM and then demodulate the AM envelope with conventional peak detectors

tuned-circuit frequency discriminators

it is the simplest form of tuned-circuit frequency discriminators that has the most nonlinear voltage-versus-frequency characteristics

Single-ended slope detector

a simply two single-ended slope detectors connected in parallel and fed 180º out of phase

Balanced slope detector

a tuned-circuit frequency discriminator whose operation is very similar to that of the balanced slope detector

Foster-Seeley discriminator (phase shift discriminator)

it is relatively immune to amplitude variations in its input signal, it has a single tuned circuit in the transformer secondary

Ratio Detector

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it requires no tuned circuits and automatically compensates for changes in the carrier frequency due to instability in the transmit oscillator

Phase-Locked Loop (PLL) FM Demodulator

it extracts the original information signal from the composite IF waveform by multiplying two quadrature (90º out of phase) signals

Quadrature FM Demodulator (coincidence detector)

the minimum dB difference in signal strength between two received signals necessary for the capture effect to suppress the weaker signal

Capture Ratio

the inherent ability of FM to diminish the effects of interfering signals

Capture Effect

it is used rather than a simple mechanical switch to reduce the static noise associated with contact bounce in a mechanical switches

Electronic push-to-talk (PTT)

CHAPTER 9: Digital Modulation

the transmission, reception, and processing of information with the use of electronic circuits

Electronic communications

the transmittal of digitally modulated analog signals (carriers) between two or more points in a communication system

Digital modulation

sometimes called for digital modulation because digitally modulated signals can be propagated through Earth’s atmosphere and used in wireless communications systems

Digital radio

a digitally modulated signal where in the information signal is digital and the amplitude of the carrier is varied proportional to the information signal

Amplitude Shift Keying (ASK)

if the frequency is varied proportional to the information signal

Frequency Shift Keying (FSK)

if the phase of the carrier is varied proportional to the information signal

Phase Shift Keying (PSK)

a highly theoretical study of the efficient use of bandwidth to propagate information through electronic communications systems

Information theory

a measure of how much information can be propagated through a communication system and is a function of bandwidth and transmission time

Information capacity

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the most basic digital symbol used to represent information

Binary digit, bit

simply the number of bits transmitted during one second and is expressed in bits per second (bps)

Bit rate

he published a paper in the Bell System Technical Journal relating the information capacity of a communication channel to bandwidth and signal-to-noise ratio

Claude E. Shannon, 1948

a term derived from the word binary M-ary

a term that is often misunderstood and commonly confused with bit rate (bps). Like bit rate, is also a rate of change; however it refers to the rate of change of a signal on the transmission medium after encoding and modulation have occurred

Baud

another name for amplitude-shift keying Digital Amplitude Modulation (DAM)

a form of constant-amplitude angle modulation similar to standard frequency modulation except the modulating signal is a binary signal that varies between two discrete voltage levels rather than a continuously changing analog waveform

Frequency-Shift Keying(FSK)

the most common circuit used for demodulating binary FSK signals

Phase-locked Loop (PLL)

another form of angle-modulated, constant-amplitude digital modulation; an M-ary digital modulation scheme similar to conventional phase modulation except with PSK the input is a binary digital signal and there are a limited number of output phases possible

Phase-shift Keying (PSK)

simplest form of PSK; a form of square-wave modulation of a continuous wave signal

Binary Phase-shift Keying (BPSK)

other names for BPSK: phase reversal keying (PRK)

biphase modulation

it acts as a phase reversing switch in a BPSK transmitter

Balanced modulator

similar to a phasor diagram except that the entire phasor is not drawn, only the relative positions of the peaks of the phasors are shown

Constellation diagram, sometimes called signal state-space diagram

a balanced modulator wherein the output signal is the product of the two input signals

Product modulator

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another form of angle-modulated constant-amplitude digital modulation. An M-ary encoding scheme where N = 2 and M = 4; four output phases are possible for a single carrier frequency

Quaternary Phase Shift Keying (QPSK), or Quadrature PSK

group of two bits Dibits

a modified form of QPSK where the waveforms on the I and Q channels are offset or shifted in phase from each other by one-half of a bit time

Offset QPSK (OQPSK)

a bit in QPSK transmitter that modulates a carrier that is in phase with the reference oscillator

I bit (hence the name “I” for “in phase” channel)

a bit in QPSK transmitter that modulates a carrier that is 90° out of phase or in quadrature with the reference carrier

Q bit (hence the name “Q” for “quadrature” channel)

three bits are encoded, forming bits, forming tribits and producing eight different output places; there are eight possible output phases

8-PSK

a code used to reduce the number of transmission errors

Gray code (maximum distance code)

a form of digital modulation similar to PSK except the digital information is contained in both the amplitude and the phase of the transmitted carrier; amplitude and phase-shift keying are combined; this reduce the likelihood or error occurring

Quadrature-amplitude Modulation (QAM)

less bandwidth is required to propagate a given bit rate

Bandwidth compression

often used to compare the performance of one digital modulation technique to another; the ratio of the transmission bit rate to the minimum bandwidth required for a particular modulation scheme

Bandwidth efficiency (information density or spectral efficiency)

the process of extracting a phase-coherent reference carrier from a receiver signal

Carrier recovery (phase referencing)

the binary data were encoded as a precise phase of the transmitted carrier

Absolute Phase Encoding

the function to determine the absolute phase of the received carrier necessary to produce a carrier at the receiver that is phase coherent with the transmit reference oscillator

Carrier Recovery Circuit

methods of carrier recovery squaring loop Costas loop remodulator

an alternative form of digital modulation where the binary input information is contained in the difference

Differential Phase-sift Keying (DPHK)

21


between two successive signaling elements rather than the absolute phase

combines encoding and modulation to reduce the probability of error, thus improving the bit error performance

Convolutional (tree) codes

the manner in which signal-state transitions are allowed to occur, and transitions that do not follow this pattern are interpreted in the receiver as transmission errors

Trellis Coding

an encoding technique used for over standard telephone circuits

Trellis Code Modulation (TCM)

the ratio of the average carrier power (the combined power of the carrier and its associated sidebands)

Carrier-to-noise Power Ratio

the energy of a single bit of information Energy per bit

the thermal noise power normalized to a 1-Hz bandwidth

Noise power density

used to compare two or more digital modulation systems that use different transmission rates (bit rates) modulation schemes

Energy per Bit-to-noise Power Density

simply the ratio of the energy of a single bit to the noise power present in 1 Hz of bandwidth

Energy per Bit-to-noise Power Density

optimum signaling format Antipodal signaling

the transmitter and receiver are not frequency or phase synchronized

Noncoherent FSK

local receiver reference signals are in frequency and

phase lock with the transmitted signalsCoherent FSK

CHAPTER 10: Digital Transmission

primary advantage of digital transmission Noise immunity

the processing of analog signals using digital methods and includes bandlimiting the signal with filters, amplitude equalization, and phase shifting

Digital Signal Processing (DSP)

one of the most important aspects of any communications system because it is costly and limited

Bandwidth

consists essentially of sampling analog information Pulse Modulation

22


signals and then converting those samples into discrete pulses and transporting the pulses from a source to a destination over a physical transmission medium

sometimes called pulse duration modulation (PDM) or pulse length modulation (PLM), as the width of a constant amplitude pulse is varied proportional to the amplitude of the analog signal at the time the signal is sampled

Pulse Width Modulation (PWM)

the position of a constant-width pulse within a prescribed time slot is varied according to the amplitude of the sample of the analog signal

Pulse Position Modulation (PPM)

the amplitude of a constant width, constant-position pulse is varied according to the amplitude of the sample of the analog

Pulse Amplitude Modulation (PAM)

the analog signal is sampled and then converted to a serial n-bit binary code for transmission; each code has the same number of bits and requires the same length of time transmission

Pulse Code Modulation (PCM)

he is credited with inventing PCM in 1937 while working for AT&T at its Paris laboratories

Alex H. Reeves

the function to periodically sample the continually changing analog input voltage and convert those samples to a series of constant-amplitude pulses that can more easily be converted to binary PCM code

Sampling circuit in a PCM transmitter

when tops of the sample pulses retain their natural shape during the sample interval making it difficult for an ADC to convert the sample to a PCM code

Natural Sampling

introduces less aperture distortion than natural sampling and requires a slower analog-to-digital converter

Flat-top sampling

the gradual discharge across the capacitor during conversion time caused by the capacitor discharging through its own leakage resistance and the input impedance of voltage follower

Droop

establishes the minimum sampling rate (fs) that can be used for a given PCM system

Nyquist sampling theorem

an impairment that occurs if minimum Nyquist sample rate is less than two times maximum analog input frequency

Alias or foldover distortion

the process of converting an infinite number of possibilities to a finite number of conditions

Quantization

23


type of code wherein the codes on the bottom half of the table are a mirror image of the codes on the top half, except for the sign bit

Folded binary code

the magnitude difference between adjacent steps Quantization interval or Quantum

it occurs if the magnitude of the sample exceeds the highest quantization interval

Overload distortion (peak limiting)

the magnitude of a quantum Resolution

any round-off errors in the transmitted signal are reproduced when the code is converted back to analog in the receiver

Quantization Error (Qe)

another name for quantization error Quantization Noise (Qn) the ratio of the largest possible magnitude to the

smallest possible magnitude that can be decoded by the digital-to-analog converter in the receiver

Dynamic Range (DR)

a numerical indication of how efficiently a PCM code is utilized; the ratio of the minimum number of bits required to achieve a certain dynamic range to the actual number of PCM bits used

Coding Efficiency

the magnitude change between any two successive code is the same

Linear codes

occurs when the input signal is at its minimum amplitude

Signal voltage-to-quantization noise voltage ratio (SQR)

during times when there is no analog input signal, the only input to the PAM sampler is random, thermal noise

Idle Channel Noise

the first quantization interval is made larger in amplitude than the rest of the steps

Midtread quantizing

the lowest-magnitude positive and negative codes have the same voltage range bas all the other codes

Midrise quantization

this type of coding compares the PAM signal to a ramp waveform while a binary counter is being advanced at a uniform rate; it requires a very fast clock

Level-at-a-time coding

this type of coding determines each digit of the PCM code sequentially; analogous to a balance where known reference weights are used to determine an unknown weight

Digit-at-a-time coding

flash encoders and are more complex; however they are more suitable for high-speed applications

Word-at-a-time coding

24


the process of compressing and then expanding Companding

amplified less than the lower-amplitude signals Compressed

amplified more than the lower-amplitude signals Expanded

it was implemented with diodes that were placed just after the low-pass filter in the PCM receiver

Analog expansion

it involves compression in the transmitter after the input sample has been converted to a linear PCM code and then expansion in the receiver prior to PCM decoding

Digital companding

a single integrated-circuit chip function to encode and decode

Codec

refers to the most of the more recently developed codecs as they include an antialising (bandpass filter), a sample-and-hold circuit, and an analog-to-digital converter in the transmit section and a digital-to-analog converter, a hold circuit, and a bandpass filter in the receive section

Combo chips

special voice encoders/decoders; are designed to reproduce only the short-term power spectrum, and the decoded time waveforms often only vaguely resemble the original input signal

Vocoders

three vocoding techniques: channel vocoder formant vocoder linear predictive coder

he developed the first channel vocoder Homer Dudley, 1928

the spectral power of most speech energy concentrates at three or four peak frequencies

Formants

a vocoder that compressed conventional speech waveforms into an analog signal with a total bandwidth of approximately 300 Hz

First channel vocoder

a vocoder that takes advantage of the fact that the short term spectral density of typical speech signals seldom distributes uniformly across the entire voice-band spectrum; it simply determines the location of

Format vocoders

a vocoder that extracts the most significant portions of speech information directly from the time waveform rather than from the frequency spectrum as with the channel and formant vocoders

Linear predictive coders

simply the data rate at which serial PCM bits are locked out of the PCM encoder onto the transmission line; it is dependent on the sample rate and the

Line speed

25


number of bits in the compressed PCM code

it uses a single-bit PCM code to achieve digital transmission of analog signals

Delta modulation

the slope of the analog signal greater than the delta modulator

Slope overload

when the original analog input signal has a relatively constant amplitude, the reconstructed signal has variation that were not present in the original signal

Granular noise

a delta modulation system where the step size of the DAC is varied, depending on the amplitude characteristic of the analog signal

Adaptive delta modulation

secondary lobes Ringing tails

an important consideration in the transmission of pulses over circuits with a limited bandwidth and a nonlinear phase response

Intersymbol interference (ISI)

it equalize the distortion for all frequencies, creating a uniform transmission medium and reducing transmission impairments

Equalizers

placed in a communication channel to bandlimit signals and reduce or eliminate predicted noise and interference; also used to produce specific pulse response

Filters

it resulted when the frequency characteristics of a communication channel depart from the normal or expected values; occurs when the peaks of pulses are reduced causing improper ringing frequencies in the time domain

Pulse distortion

simply the superposition of a series of harmonically related sine waves with specific amplitude and phase relationships

Pulse

it occurs if the relative phase relations of the individual sine waves are altered

Phase distortion

a convenient technique for determining the effects of the degradations introduced into the pulses as they travel to the regenerator

Eye pattern

CHAPTER 11 : Digital T- Carriers and Multiplexing

the transmission of information from one or ore source to one or more destination over the same transmission medium; the transmission medium may

Multiplexing

26


be a metallic wire pair, a coaxial cable, a PCS mobile telephone, a terrestrial microwave radio system, a satellite microwave system, or an optical fiber cable

a rather unsophisticated form of multiplexing that simply constitutes propagating signals from different sources on different cables that are contained within the same trench

Space-division multiplexing (SDM)

transmissions from multiple sources occur on the same facility but not at the same time; transmissions from various sources are interleaved in the time domain

Time division multiplexing

a communication system that uses digital pulse rather than analog signals to encode information

Digital carrier

stands for transmission one and specifies a digital carrier system using PCM-encoded analog signals

T1

occurs once per frame and is recovered in the receiver where it is used to maintain frame and sample synchronization between the TDM transmitter and receiver

Additional bit (framing bit)

consists of 24 193-bit frames totaling 4632 bits, of which 24 are bits

Extended superframe format

a digital interface that provides the physical connection to a digital carrier network

Data service unit/channel service unit (DSU/CSU)

can handle bit-rate conversions on both directions Multiplexers/demultiplexers (muldem)

provides a convenient place to make patchable interconnects and perform routine maintenance and troubleshooting

Digital cross-connect (DSX)

a low-quality video transmission for use between nondedicated subscribers

Picturephone

involves converting standard logic levels to a form more suitable to telephone line transmission

Digital line encoding

can be used to categorize the type of transmission Duty cycle

if the binary pulse is maintained for the entire bit time Nonreturn to zero (NRZ)

if the active time of the binary pulse is less than 100% of the bit time

Return to zero (RZ)

a condition when a long string of either logic 1s or 0s produces a condition in which a receive may lose its amplitude reference for optimum discrimination between received 1s and 0s

DC wandering

27


a popular type of line encoding that produces a strong timing component for clock recovery and does not cause dc wandering

Digital biphase (Manchester code or diphase)

used for encoding SMPTE (Society of Motion Picture and Television Engineers) time-code data for recording on videotapes

Biphase M

forms of delay-modulated codes where a logic 1 condition produces a transition in the middle of the clock pulse and a logic 0 produces no transition at the end of the clock intervals unless followed by another logic 0

Miller codes

used for the transmission of PCM-encoded time-division multiplexed digital signals

T carriers

filters and shapes the incoming digital signal and raises its power level so that the regenerator circuit can make a pulse-no pulse decision

Amplifier/equalizer

reproduces the clocking information from the received data and provides the proper timing information to0 the regenerator

Timing clock recovery

simply a threshold detector that compares the sampled voltage received to a reference level and determines whether the bit is a logic 1 or logic 0

Regenerative repeater

were designed to combine PCM and TDM techniques for short-haul transmission of 24 64-kbps channels with each channel capable of carrying digitally encoded voice-band telephone signals or data

T1 carrier systems

a technique used to ensure that sufficient transitions occur in the data to maintain clock synchronization

Binary eight zero substitution (B8ZS)

the same as added-digit framing except that digits are added in groups or words instead of as individual bits

Added-channel framing

2 methods of interleaving PCM transmissions: bit interleaving word interleaving

a large-scale integration chip designed for use in the telecommunications industry for private branch exchanges, central office switches, digital handsets, voice store-and-forward systems and digital echo suppressors

Codec

combined codec chips; provide the analog-to-digital and the digital-to-analog conversions and the transmit and receive filtering necessary to interface a

Combo chip

28


full-duplex (four wire) voice telephone circuit to the PCM highway of a TDM carrier system

multiple sources that originally occupied the same frequency spectrum are each converted to a different frequency band and transmitted simultaneously over a single transmission medium

Frequency-division multiplexing (FDM)

describes the modulating signal (intelligence) in a communications system

Baseband

a double side-band suppressed carrier modulator Balanced modulator

a void band of frequencies that is not included within any supergroup band

Guard bands

involves the transmission of multiple digital signal using several wavelengths without their interfering with one another

Wavelength division multiplexing (WDM)

separate signals with different wavelengths in a manner similar to the way filters separate electrical signals of different frequencies

Demultiplexers or splitters

direct signals of a particular wavelength to a specific destination while not separating while not separating all the wavelengths present on the cable

WDM routers

specific wavelengths are separated from the other optic signal by reflecting them at different angles

Diffraction gratings or prisms

a mirror with a surface that has been coated with a material that permits light of only one wavelength to pass through while reflecting all other wavelengths

Dichroic filter

CHAPTER 12: Metallic Cable Transmission Media

two general category of transmission media guided unguided

transmission media with some form of conductor that provides a conduit in which electromagnetic signals are contained

Guided transmission media

it transports signals using electric current Copper

a guided transmission medium and can be any Cable transmission medium

29


physical facility used to propagate electromagnetic signals between two locations in a communication system

include open wire, twin lead and twisted-pair copper wire as well as coaxial cable

Metallic transmission medium

the most common means of interconnecting devices in local area networks transmission of digital signals

Cable transmission medium

a metallic conductor system used to transfer energy from one point to another using electrical current flow; two or more electrical conductors separated by a nonconductive insulator (dielectric); can be as short as a few inches or span several thousand miles; can be used to propagate dc or low-frequency ac or to propagate very high frequencies

Transmission lines

the displacement (amplitude) is in the direction of propagation; surface wave of water

Longitudinal waves

the direction of propagation of displacement is perpendicular to the direction of propagation; electromagnetic

Transverse waves

propagation of electrical power along a transmission line occurs in the form of ______________________

Transverse electromagnetic (TEM) waves

the E and H fields are perpendicular to each other (at 90° angles) at all points

Space quadrature

electromagnetic waves that travel along a transmission line from the source to the load

Incident waves

those that travel from the load back toward the source

Reflected waves

it travel at approximately 1100 feet per second in the normal atmosphere

Sound waves

the rate at which the periodic wave repeats Frequency

the distance of one cycle occurring in space Wavelength

with two-wire balanced lines, both conductors carry current; however, one conductor carries the signal, and the other conductor is the return path

Differential or Balanced signal transmission

currents that flow in opposite directions in a balanced wire pair

Metallic circuit currents

currents that flow in the same direction Longitudinal currents

cancellation of common mode signals Common mode rejection

30


with an unbalanced transmission line, one wire is at ground potential, whereas the wire is at signal potential

Single-ended or Unbalanced signal transmission

a circuit device used to connect a balanced transmission line to an unbalanced load

Balun (balanced to unbalanced)

are comprised of two or more metallic conductors separated by a nonconductive insulating material called a dielectric

Parallel-wire transmission lines

two-wire parallel conductors; consist simply of two parallel wires, closely spaced and separated by air; its advantage is its simple construction; there is no shielding, radiation losses are high, and the cable is susceptible to picking up signals through mutual induction

Open-wire transmission lines

occurs when a signal on one cable interferes with a signal on an adjacent cable

Crosstalk

it is called if the sleeve is woven into a mesh Braid

it is given in dB of loss per 100 meters of cable with respect to frequency

Attenuation

given in dB of attenuation between the transmit signal and the signal is returned due to crosstalk with higher dB values indicating less crosstalk

Crosstalk

the name given to the area between the ceiling and the roof in a single building or between the ceiling and the floor of the next higher level in a multistory building

Plenum

plenum cables that coated with Teflon, which does not emit noxious chemicals when ignited, or special fire-resistant PVC

Plenum-grade PVC

a coaxial cable with one layer of foil insulation and one layer of braided shielding

Dual shielded

consist of two layers of foil insulation and two layers of braided metal shielding

Quad shielding

cables that are relatively expensive to manufacture and to minimize losses, the air insulator must be relatively free of moisture

Rigid-air filled coaxial

have lower losses than hollow cables and are easier to construct, install and maintain

Solid coaxial cables

sometimes referred to as “bayonet mount” as they can be easily twisted on or off

BNC connectors

31


are threaded and must be screwed on and off n-type connectors

the transmission characteristics of a transmission line Secondary constants

defined as the impedance seen looking into an infinitely long line or the impedance seen looking into a finite length of line that is terminated in a purely resistive load with a resistance equal to the characteristic impedance of the line

Characteristic impedance (surge impedance)

used to express the attenuation (signal loss) and the phase shift per unit length of a transmission line

Propagation constant (propagation coefficient)

defined simply as the ratio of the actual velocity of propagation of an electromagnetic wave through a given medium to the velocity of propagation through a vacuum (free space)

Velocity factor (velocity constant)

the relative dielectric constant of air 1.0006

transmission lines designed to intentionally introduce a time delay in the path of an electromagnetic wave

Delay lines

a phenomenon that when current flows through an isolated round wire, the magnetic flux associated with it is in the form of concentric circles surrounding the wire core

Skin effect

the ratio of the ac resistance to the dc resistance of a conductor

Resistance ratio

it caused a difference of potential between two conductors of metallic transmission line

Dielectric heating

the energy radiated if the separation between conductors in a metallic transmission is an appreciable fraction of a wavelength, the electrostatic and electromagnetic fields that surround the conductor cause the line to act as if it were an antenna and transfer energy to a nearby conductive material

Radiation loss

it occurs whenever a connection is made to or from a transmission line or when two sections of transmission line are connected together

Coupling loss

a luminous discharge that occurs between the two conductors of a transmission line when the difference of potential between them exceeds the breakdown voltage of the dielectric insulator

Corona

32


voltage that propagates from the source toward the load

Incident voltage

voltage that propagates from the load toward the source

Reflected voltage

a transmission line with no reflected power Flat or nonresonant line

defined as the ratio of the maximum voltage to the minimum voltage or the maximum current to the minimum current of a standing wave on a transmission lin

Standing Wave Ratio (SWR)

used to match transmission lines to purely resistive loads whose resistance is not equal to the characteristic impedance of the line

Quarter-wavelength

simply a piece of additional transmission line that is placed across the primary line as close to the load as possible; the susceptance is to tune out the susceptance of the load

Transmission-line stub

a technique that can be used to locate an impairment in a metallic cable

Time-domain reflectometry (TDR)

simply a flat conductor separated from a ground plane by an insulating dielectric material

Microstrip

simply a flat conductor sandwiched between two ground planes; less likely to radiate; losses are lower

Stripline

CHAPTER 13 : Optical Fiber transmission Media

the bandwidth of an analog communications system is expressed as a percentage of its carrier frequency

Bandwidth utilizations ratio

it was a device constructed from mirrors and selenium detectors that transmitted sound waves over a beam of light

Photophone

he successfully transmitted images through a single glass fiber

H. Lamm

they experimented with light transmission through A.C.S van Heel

33


bundles of fibers H.H. Hopkins N.S. Kapany

it was when the three scientists experimented on a bundle of glass fiber the transmission of light

1951

he coined the term fiber optics N.S. Kapany

they wrote a paper describing how it was possible to use stimulated emission for amplifying light waves as well as microwaves

Charles H. Townes Arthur L. Schawlow

defined as the maximum angle in which external light rays may strike the air/glass interface and still propagate down the fiber

Acceptance angle

other term used for acceptance angle Acceptance cone half-angle

closely related to acceptance angle and is figure of merit commonly used to measure the magnitude of the acceptance angle

Numerical aperture

the refractive index of a glass core 1.5

only one path for light rays to take down a cable Single mode

more than one path Multimode

the term that means path in fiber optics technology Mode

these parameters dictate how a light propagates mode or propagation index profile of fiber

the graphical representation of the magnitude of the refractive index across the fiber

Index profile

has a central core with a uniform refractive index Step-index fiber

no cladding and the refractive index of the core is nonuniform

Graded-index fiber

has a central core that is smaller in diameter that any of the multimode cables

Single-mode step-index fiber

type of fiber has a large light to fiber aperture and allows more external light to enter the cable

Multimode step-index optical fiber

the light rays that make up the pulse spread out in time, causing a corresponding reduction in the pulse amplitude and stretching of pulse width

Pulse spreading

other term used for pulse spreading Pulse-width dispersion

UPRZ is the acronym for _____ Unipolar return to zero

a condition wherein the energy from pulse a were UPNRZ transmission

34


to fall back one-half of a bit time, it would interfere with pulse b

UPNRZ is the acronym for _____ Unipolar nonreturn to zero

the light energy from pulse a were to fall back one bit time, it would interfere with pulse b and change what was a logic 0 to logic 1

UPRZ

the difference between the absolute delay times of the fastest and slowest rays of light propagating down a fiber of unit length

Pulse spreading constant

equal to the pulse spreading constant times the total fiber length

Total pulse spread

caused by imperfect physical connections Coupling losses

the other term used for gap displacement End separation

the typical value of loss for an angular displacement less than 2

Less 0.5 dB

these are the spectral widths of a standard LED 30 nm to 50 nm

the wavelength equivalent of bandwidth Linewidth

a pn junction diode usually made from a semiconductor material such as aluminum gallium arsenide or gallium arsenide phosphide

LED

a group iv atom used to produce light wavelengths in the 800 nm range

Arsenide

a small batterylike device that produced a dc output voltage proportional to the amount of light received

Photocell

a special high-intensity, single frequency light source. it produces a very narrow beam of brilliant light of a specific wavelength (color); it can penetrate atmospheric obstacles better than other type of light,

Laser

commonly used as a light source, this is a semiconductor device that puts out a low-intensity red light beam

LED

another commonly used light source, that generates an extremely intense single frequency light beam

Solid-state laser

light sensitive device, used to detect the light pulses; converts the light pulses to electrical signal

Photocell or light detector

35


CHAPTER 14: Electromagnetic Wave Propagation

a form of electromagnetic radiation that consist of traveling electric and magnetic fields

Radio waves

orientation of the electric field vector in respect to the surface of earth

Polarization

the polarization remains constant Linear polarization

a form of linear polarization when the electric field is propagating parallel to the Earth’s surface

Horizontal polarization

if the electric field is propagating perpendicular to the Earth’s surface

Vertical polarization

if the polarization vector rotates 360° as the wave moves one wavelength through the space and the field strength is equal at all angles of polarization

Circular polarization

when the field strength varies with changes in polarization

Elliptical polarization

shows a surface of constant phase of electromagnetic waves; formed when points of equal phase on rays propagated from the same source are joined together

Wavefront

a single location from which rays propagate equally in all directions

Point source

an invisible force field produced by a magnet, such as a conductor when current is flowing through it

Magnetic field

the rate at which energy passes through a given surface area in free space

Power density

also an invisible force fields produced by a difference in voltage potential between two conductors

Electric fields

a source that radiates power at a constant rate uniformly in all directions

Isotropic radiator

the power density is inversely proportional to the square of the distance from the source

Inverse square law

reduction in power density and occurs in free space as well as the Earth’s atmosphere

Attenuation

36


the reduction of power where in it contains particles that can absorb electromagnetic energy

Absorption loss

the reduction in power density due to nonfree-space propagation

Absorption

sometimes referred to as the bending of the radio-wave path

Refraction

the angle formed between the incident wave and the normal

Angle of incidence

the angle formed between the refracted wave and the normal

Angle of refraction

the ratio of the velocity of propagation of a light ray in free space to the velocity of propagation of a light ray in a given material

Refractive index

the ratio of the reflected to the incident voltage intensities

Reflection coefficient

a condition when an incident wavefront strikes an irregular surface, it randomly scattered in many directions

Diffuse reflection

reflection from a perfectly smooth surface Specular (mirrorlike) reflection

the fraction of power that penetrates medium two Absorption coefficient

states that a semirough surface will reflect as if it were a smooth surface whenever the cosine of the angle of incidence is greater than /8d, where d is the depth of the surface irregularity and is the wavelngth of the incident wave

Rayleigh criterion

defined as the modulation or redistribution of energy within a wavefront when it passes near the edge of an opaque object; the phenomenon that allows light or radio waves to propagate around corners

Diffraction

states that every point on a given spherical wavefront can be considered as a secondary point source of electromagnetic waves from which other secondary waves are radiated outward

Huygen’s principle

occurs whenever two or more waves simultaneously occupy the same point in space; states that the total voltage intensity at a given point in space is the sum of the individual wave sectors

Linear superposition

electromagnetic waves traveling within Earth’s atmosphere

Terrestrial waves

37


communications between two or more points on Earth

Terrestrial radio communications

direct and ground-reflected waves together Space waves

the cumulative sum of the direct, ground-reflected, and surface waves

Ground wave

depends on the presence of the ionized layers above the Earth that return some of the energy that otherwise would be lost in outer space

Sky wave

an earth-guided electromagnetic wave that travels over the surface of Earth;

Surface waves

travel essentially in a straight line between the transmit and received antennas

Direct waves

occurs when the density of the lower atmosphere is such that electromagnetic waves are trapped between it and Earth’s surface

Duct propagation

electromagnetic waves that are directed above the horizon

Sky waves

another term for sky wave propagation Ionospheric propagation

the lowest layer of the ionosphere and is located approximately between 30 miles and 60 miles above Earth’s surface

D layer

located approximately between 60 miles and 85 miles above the Earth’s surface; sometimes called Kennelly-Heavyside layer

E layer

made up of two layers F1 and F2 layers; during daytime, F1 layer is located between 85 miles and 155 miles above the earth’s surface; the F2 layer is located 85 miles to 185 miles above the Earth’s surface during winter and 155 miles to 220 miles in the summer

F layer

defined as the highest frequency that can be propagated directly upward and still be returned to earth by the ionosphere; depends on the ionization density and, therefore varies with the time of day and season

Critical frequency (fc)

the height above earth’s surface from which a refracted wave appears to have been reflected

Virtual height

the highest frequency that can be used for sky wave propagation between two specific points on Earth’s surface

Maximum usable frequency (MUF)

38


a law that assumes a flat Earth and a flat reflecting layer can never exist

Secant law

85% of the MUF that provides more reliable communications

Optimum working frequency (OWF)

defined as the minimum distance from a transmit antenna that a sky wave at a given frequency will be returned to Earth

Skip distance

usually of little significance, as it tends to be much weaker than the lower ray because it spreads over a much larger area than the lower ray

Pedersen ray

the area between where the surface waves are

completely dissipated and the point where the first sky wave returns to Earth

Quiet or skip zone

often defined as the loss incurred by an electromagnetic wave as it propagates in a straight line through a vacuum with no absorption or reflection of energy from nearby objects

Free-space path loss

it occurs simply because of the inverse square law Spreading loss

loss attributed to several different phenomena and can include both short- and long- term

Fading

an additional loss is added to the normal path loss to accommodate temporary fading

Fade margin

CHAPTER 15 : Antennas and Waveguide

the plane parallel to the mutually perpendicular lines of the electric and magnetic fields

Wavefront

the ratio of radiate to reflected energy Radiation efficiency

antenna wherein the conductors are spread out in a straight line to a total length of one-quarter wavelength

Quarter-wave antenna (vertical monopole sometimes called Marconi antenna)

a half wave dipole Hertz antenna

meaning two dipoles that is used to radiate more energy by simply spreading the conductors farther apart

Dipole

a basic antenna that cannot amplify a signal, at least not in the true sense of the word

Passive reciprocal device

a special coupling device that can be used to direct Diplexer

39


the transmit and receive signals and provide the necessary isolation

a polar diagram or graph representing field strength or power densities at various angular positions relative to an antenna

Radiation pattern

primary beam in a 90 direction Major lobe

represent undesired radiation or reception Minor lobe

the lobe that receives the most energy Front lobe

lobes adjacent to the front lobe (the 180 minor lobe)

Side lobes

lobes in a direction exactly opposite the front lobe Back lobe

ratio of the front lobe power to the back lobe power Front-to-back ratio

the ratio of the front lobe to a side lobe Front-to-side ratio

the line bisecting the major lobe, or pointing from the center of the antenna in the direction of maximum radiation

Line of shoot (point of shoot)

refers to the filed that is close to the antenna Near field

refers to the field pattern that is at great distance Far field

sometimes called to near field Induction field

sometimes called for far field because power that reaches the far field continues to radiate outward and is never returned to the antenna

Radiation field

an ac antenna resistance and is equal to the ratio of the power radiated by the antenna to the square of the current at its feedpoint

Radiation resistance

the ratio of the power radiated by an antenna to the sum of the power radiated and the power dissipated or the ratio of the power radiated by the antenna to the total input power

Antenna efficiency

the ratio of the power density radiated in a particular direction to the power density radiated to the same point by a reference antenna, assuming both antennas are radiating the same amount of power

Directive gain

the maximum directive gain Directivity

the same as directive gain except that the total power fed to the antenna is used; it is assumed that the given antenna and the reference antenna is lossless

Power gain

40


defined as an equivalent transmit power; the equivalent power that an isotropic antenna would have to radiate to achieve the same power density in the chosen direction at a given point as another antenna

Effective Isotropic Radiated Power (EIRP)

the power density in space and a somewhat misleading quantity

Captured power density

refers simply to the orientation of the electric field radiated from it.

Polarization of an antenna

simply the angular separation between the two half-power points on the major lobe of an antenna’s plane radiation pattern, usually taken in one of the “principal” planes

Beamwidth

vaguely defined as the frequency range over which antenna operation is “satisfactory”

Antenna bandwidth

normally taken as the difference between the half-power frequencies but sometimes refers to variations in the antenna’s input impedance

Bandwidth

the point on the antenna where the transmission line is connected

Feedpoint

the feedpoint presents an ac load to the transmission line

Antenna input impedance

an electrically short dipole Elementary doublet

a multiple of quarter-wavelength long and open circuited at the far end

Resonant antenna

a monopole antenna one-quarter wavelength long, mounted vertically with the lower end either connected to ground or grounded through the antenna coupling network

Marconi antenna

a wire structure placed below the antenna and erected above the ground; should be insulated from earth ground

Counterpoise

a technique wherein the physical length of an antenna remains unchanged although its effective electrical length is increased

Loading

a coil (inductor) added in series with a dipole antenna that effectively increases the antenna’s electrical length

Loading coil

a technique where in a metallic array that resembles a spoked wheel is placed on top of the antenna

Top loading

41


formed when two or more antenna elements are combined to form a single antenna

Antenna array

an individual radiator, such as a half- or quarter- wave dipole

Antenna element

elements that are directly connected to the transmission line and receive power from or are driven by source

Driven elements

not connected to the transmission line; they receive energy only through mutual induction with a driven element or another parasitic element

Parasitic element

a parasitic element that is longer than the driven element from which it receives energy; effectively reduces the signal strength in its direction and increases it in the opposite direction

Reflector

a parasitic element that is shorter than its associated driven element; increases field strength in its direction and reduces it in the opposite direction

Director

one of the simplest types of antenna rays; made by simply placing a several resonant dipoles of equal size in parallel with each other and in a straight line

Broadside array

essentially the same element configuration as the broadside array except that the transmission line is not crisscrossed between elements; as a result the field are additive in line with the plane of the array

End-fire array

a nonresonant antenna that is capable of operating satisfactorily over a relatively wide bandwidth making it ideally suited for HF transmission

Rhombic antenna

essentially a single antenna made up of two elements

Folded dipole

dipole elements larger in diameter; Fat dipole

antenna named after two Japanese scientists who invented it and describe its operation

Yagi-uda antenna

a linear array consisting of a dipole and two or more parasitic elements: one reflector and one or more directors

Yagi antenna

formed by placing two dipoles at right angles to each other 90° out of phase

Turnsile antenna

a class of frequency-independent antennas where in its primary advantage is the independence of their radiation and radiation pattern to frequency; from the initial work of V. H. Rumsey, J. D. Dyson,

Log-periodic antennas

42


R. H. DuHamel and D.E. Isbell

the ratio of the highest to the lowest frequency over which antenna will satisfactorily operate

Bandwidth ratio

simply a single-turn coil of wire that is significantly shorter than one wavelength and carries RF current

Loop antenna

a group of antenna or a group of antenna arrays that, when connected together function as a single antenna whose beamwidth and direction can be changed electronically without having to physically move any of the individual antennas or antenna elements within the array

Phased array antenna

a broadband VHF or UHF antenna that is ideally suited for applications for which radiating circular rather than horizontal or vertical polarized electromagnetic waves; used as a single element antenna or stacked horizontally or vertically in an array to modify its radiation pattern by increasing the gain and decreasing the beamwidth of the primary lobe

Helical antenna

electromagnetic radiation is in a direction at right angles to the axis of the helix

Normal mode

radiation is in the axial direction and produces a broadband, relatively directional pattern

Axial mode

defined as the ratio of its maximum gain in the forward direction to its maximum gain in its backward direction

Front-to-back ratio

used with point-to-point microwave systems Highly directional antennas

provide extremely high gain and directivity and are very popular for microwave radio and satellite communications skills

Parabolic reflector antennas

two main parts of parabolic antenna: parabolic reflector feed mechanism

resemble the shape of a plate or dish; a plane curve that is defined as the locus of a point that moves so that its distance from another point added to its distance from a straight line is of constant length

Parabolic reflectors (parabolic dish, dish antennas)

the ratio of the focal length to the diameter of the mouth of the parabola

Aperture ratio

43


the resulting curved surface dish Paraboloid

energy near the edge of the dish does not reflect but rather is diffracted around the edge of the dish

Spillover or leakage

considers both the radiation pattern of the primary radiator and the effect

Aperture efficiency

the ratio of the focal length of the antenna to the reflector diamtere

Aperture number

houses the primary antenna which radiates electromagnetic waves toward the reflector

Feed mechanism

three primary types of feed mechanism for parabolic antennas:

center feed horn feed cassegrain feed

the primary antenna is placed at the focus Center feed

the primary antenna is a small horn antenna rather than a simple dipole or dipole array

Horn feed

the primary radiating source is located in or just behind a small opening at the vertex of the paraboloid rather than at the focus

Cassegrein feed

consists of a cone that is truncated in a pice of circular waveguide; the waveguide in turn connects the antenna to either the transmitter or the receiver

Conical horn antenna

a hollow conductive tube, usually rectangular in cross section but sometimes circular or elliptical

Waveguides

the velocity at which a wave propagates; the velocity at which information signals of any kind are propagated; also the velocity at which energy is propagated; can be measured by determining the time it takes for a pulse to propagate a given length of a waveguide

Group velocity

velocity at which the wave changes phase; the apparent velocity of a particular phase of the wave; the velocity with which a wave changes phase in a direction parallel to a conducting surface; such as the walls of a waveguide

Phase velocity

minimum frequency of operation; the absolute limiting frequency; frequencies above the cutoff frequency will not be propagated by the waveguide

Cutoff frequency

maximum wavelength that they can propagate; defined as the smallest free-space wavelength that

Cutoff wavelength

44


is just unable to propagate in the waveguide

the travel of electromagnetic waves down a waveguide in different configurations

Propagation of modes

means that the electric field lines are everywhere transverse (perpendicular to the guide walls)

TE

waveguides used in radar and microwave applications when it is necessary or advantageous to propagate both vertically and horizontally polarized waves in the same waveguide

Circular waveguide

waveguide that is more expensive to manufacture than a standard rectangular waveguide; however it allows operation at lower frequencies for a given size

Ridged waveguide

consists of a spiral-wound ribbons of brass or copper; used extensively in microwave test equipment

Flexible waveguide

CHAPTER 16: Telephone Instruments and Signal

a part of global communications network which uses telephone or a data modem on a telephone network

Public telephone network (PTN)

PTN that interconnects subscribers through one or more switches

Public switch telephone network (PSTN)

the simplest and most straightforward form of telephone service which involves subscribers accessing the public telephone network through a pair of wires

Plain old telephone service (POTS)

simply an unshielded twisted-pair transmission line (cable pair) consisting of two insulated conductors twisted together; generally comprised of several lengths of copper wire interconnected at junction and cross-connect boxes located in manholes, back alleys, or telephone equipment rooms with large buildings and building complexes

Subscriber loop (local loop)

means to connect a telephone set at a subscriber’s location to the closest telephone office, which is commonly called an end office, local exchange office, or central office

Subscriber loop

enables the subscriber to access the public Electronic switching system

45


telephone network (ESS)

the quality of transmission over a telephone depends on:

received volume relative frequency

response of the telephone circuit

degree of interference

helps prevent the speaker from talking too loudly Sidetone/talkback

pair of wires connecting a subscriber to the closest telephone office

Local loop

one wire on the local loop Tip come from the ¼-inch-diameter two-conductor

phone plugs and patch cords used at telephone company switch-boards to interconnect and test circuits

Tip and Ring

standards for registered jacks and is sometimes called as RJ-XX; a series of telephone connection interfaces (receptacle and plug) that are registered with the U.S. FCC

RJ

the most common telephone jack in use today and can have up to six conductors

RJ-11

reasons why a dc voltage was used rather than an ac voltage

prevent power supply hum

allow service to continue in the event of a power outage

people were afraid of ac

voltage selected to minimize electrolytic corrosion on the loop wires; used for supervisory signaling and to provide talk battery for the microphone in the telephone set

-48 Vdc

examples of supervisory signals on-hook off-hook dial pulsing

placed directly across the tip and ring of the local loop; the purpose of the ringer is to alert the destination party of incoming calls

Ringer circuit

a simple single-throw, double pole (STDP) switch placed across the tip and ring; mechanically connected to the telephone is idle (on hook) is open; when the telephone is in use (off hook) is closed completing an electrical path through the microphone between the tip and ring of the local loop

On/off hook circuit (switch)

46


combinations of passive components that are used to regulate the amplitude and frequency response of the voice signals

Equalizer

the receiver for the telephone; converts electrical signals received from the local loop to acoustical signals (sound waves) that can be heard and understood by a human being; connected to the local loop through the hybrid network; typically enclosed in the handset of the telephone along with the microphone

Speaker

the transmitter for the telephone; converts acoustical signals in the form of sound pressure waves from the caller to electrical signals that are transmitted into the telephone network through the local subscriber loop

Microphone

a special balanced transformer used to convert a two-wire circuit (the local loop) into a four-wire circuit (the telephone set) and vice versa, thus enabling full duplex operation over a two-wire circuit

Hybrid network (hybrid coil or duplex coil)

enables the subscriber to output signals representing digits and this enables the caller to enter the destination telephone number; either an electronic dial-pulsing circuit or a Touch-Tone keypad which sends various combinations of tones representing the called digits

Dialing circuit

are acknowledgement and status signals that ensure the processes necessary to set up and terminate a telephone call are completed in an orderly and timely manner

Call progress tones and call progress signals

the exchange of signaling messages over local loops between stations (telephone) and telephone company switching machines

Station signaling

the exchange of signaling messages between switching machines

Interoffice signaling

indicate a request for service such as going off hook or ringing the destination telephone

Alerting signals

provide call status information, such as busy or ring-back signals

Supervising signals

provide information in the form of announcements such as number changed to another number, a number no longer in service

Controlling signals

provide the routing information such as calling and called numbers

Addressing signals

47


Call Progress Tone Summary

Tone or Signal

Frequency Duration/Range

Dial tone 350 Hz plus 440 Hz Continuous DTMF 697 Hz, 770 Hz, 852 Hz, 941

Hz, 1209 Hz, 1336 Hz, 1477 Hz, 1633 Hz

Two of eight tonesOn, 50-ms minimumOff, 45-ms minimum3-s minimum

MF 700 Hz, 900 Hz, 1100 Hz,1300 Hz, 1500 Hz, 1700 Hz

Two of six tonesOn, 90-ms minimum120-ms maximum

Dial pulses Open/closed switch On, 39 msOff, 61 ms

Station busy 480 Hz plus 620 Hz On, 0.5 sOff, 0.5 s

Equipment busy

480 Hz plus 620 Hz On, 0.2 sOff, 0.3 s

Ringing 20 Hz, 90 vrms (nominal) On, 2 sOff, 4 s

Ring-back 440 Hz plus 480 Hz On, 2 sOff, 4 s

Receiver on hook

Open loop Indefinite

Receiver off hook

Dc current 20 mA minimum80 mA maximum

Receiver-left-off- hook alert

1440 Hz, 2060 Hz, 2450 Hz, 2600 Hz

On, 0.1 sOff, 0.1 s

a 2600-Hz frequency tone placed on a circuit to indicate the circuit is not currently in use

IDLE signal

a multifrequency control tone comprised of 1100 Hz plus 1700 Hz ranging from 90 ms to 120 ms; used to indicate the beginning of a sequence of MF digits

Key Pulse (KP) signal

the method originally used to transfer digits from a telephone set to the local switch

Dial pulsing (rotary dial pulsing)

is sent from the switching machine back to the Station busy signal

48


calling station whenever the called telephone number is off hook; a two-tone signal comprised of 480Hz and 620 Hz

sent from the switching machine back to the calling station whenever the system cannot complete the call because of equipment unavailability

Equipment busy signal (congestion tone/no-circuits-available)

whenever the system is overloaded and more calls are being placed than can be completed

Blocking

sent from a central office to a subscriber whenever there is an incoming call; the purpose is to ring the bell in the telephone set to alert the subscriber that there is an incoming call

Ringing signal

sent back to the calling party at the same time the ringing signal is sent to the called party; the purpose is to give some assurance to the calling party that the destination telephone number has been accepted, processed, and is being rung

Ring-back signal

simply tones that operate cords attached to the handset; a full duplex, battery-operated , portable radio transceiver that communicates directly with a stationary transceiver located somewhere in the subscriber’s office

Cordless telephone

enables the destination of a telephone call to display the name and telephone number of the calling party before the telephone is answered; allows subscribers to screen incoming calls and decide whether they want to answer the telephone; a simplex transmission sent from the central office switch over the local loop to a caller ID display unit at the destination

Caller ID

simplex wireless communications system deigned to alert subscribers of awaiting messages; relay radio signals and messages from wire-line and cellular telephones to subscribers carrying portable receivers

Paging transmitters

CHAPTER 17 : The Telephone Circuit

the network bandwidth for a standard voice-band message channel

4 kHz

the only facility required by all voice-band circuits, as it is the means by which subscriber locations are

Local subscriber loop

49


connected to the local telephone company

a metallic transmission line comprised of two insulated copper wires (a pair) twisted together

Local loop

an actual loss of signal strength Attenuation

occurs when two or more frequencies undergo different amounts of phase shift

Phase distortions

depend on the wire diameter, conductor spacing, dielectric constant of the insulator separating the wires and the conductivity of the wire

Transmission characteristics

refers to the electrical characteristics of a cable uniformly distributed along its length

Distributed parameters

the largest cable used in a local loop, usually 3600 pair of copper wire placed underground or in conduit

Feeder cable (F1)

a cross-connect point used to distribute the larger feeder cable into smaller distribution cables

Serving area interface (SAI)

a smaller version of a feeder cable containing less wire pairs

Distribution cable (F2)

a device that serves as the demarcation point between local telephone company responsibility and subscriber responsibility for telephone service

Subscriber or standard network interface (SNI)

the final length of cable pair that terminates at the SNI

Drop wire

that portion of the local loop that is strung between poles

Aerial

the location where individual cable pairs within a distribution cable are separated and extended to the subscriber’s location on a drop wire

Distribution cable and drop-wire cross-connect point

an irregularity found in cables serving subscriber locations; unused sections of cable that are connected in shunt to a working cable pair

Bridge tap

the basic yardstick used for making power measurements in communications

Decibel, dB

defined as the optimum level of a test tone on a channel on a channel at some point in a communications system

Transmission level point (TLP)

the ratio in dB of the power of a signal at that point to the power the same signal would be at a 0-dBm transmission level point

Transmission level (TL)

50


a parameter used as a reference for data transmission

Data level point (DLP)

used primarily in Europe; assumes a perfect receiver; therefore, its weighting curve corresponds to the frequency response of the human ear only

Psophometric noise weighting

apply to dedicated private-line data circuits that utilize the private sector of the public telephone network – circuits with bandwidths comparable to those of standard voice-grade telephone channels that do not utilize the public switched telephone network

Transmission parameters

direct connections between two or more locations Private-line circuits

the difference in circuit gain of a reference frequency

Attenuation distortion (frequency response, differential gain and 1004-Hz deviation)

an indirect method of evaluating the phase delay characteristics of a circuit

Envelope delay distortion

the process used to improve a basic telephone channel; improves the high frequency response of a message channel and reduces power loss

Line conditioning

specifies the maximum limits for attenuation and envelope delay distortion; pertains to line impairments for which compensation can be made with filters and equalizers

C-type conditioning

telephone systems provided by local telephone companies dedicated to a single customer, usually with a large number of stations

Private switched networks

a relatively low-capacity switching machine where the subscribers are generally limited to stations within the same building or building complex

Private branch exchange (PBX)

the time delay encountered by a signal as it propagates from a source to a destination

Propagation time

delay measured in angular units, such as degrees or radians

Phase delay

the actual time required for a particular frequency to propagate from a source to a destination through a communications channel

Absolute phase delay

evaluate not the true phase-versus-frequency characteristics but rather the phase of a wave that is the result of a narrow band of frequencies

Envelope delay

the phase difference at the different carrier frequencies; indicates the relative delays of the various carrier frequencies with respect to the

Envelope delay distortion

51


reference frequency

neither reduces the noise on a circuit nor improves the signal-to-noise ratio; a requirement and does not add anything to the circuit and it cannot be used to improve a circuit; it simply places higher requirements on circuits used for high-speed data transmission

D-type conditioning

unwanted multiples of the transmitted frequencies Harmonic distortion

cross products [sums and differences] of the transmitted frequencies

Intermodulation distortion (fluctuation noise or cross-modulation noise)

the purpose is to simulate the combined signal power of a standard voice-band data transmission

1004-Hz test tone

determine the average weighted rms noise power C-message noise

differ from standard C-message noise measurements only in the fact that a holding tone is applied to the transmit end of the circuit while the noise measurement is taken

C-notched noise

ensures that the circuit operation simulates a loaded voice or data transmission

Holding current

a communications term that indicates the presence of a signal power comparable to the power of an actual message transmission

Loaded

characterized by high-amplitude peaks (impulses) of short duration having an approximately flat frequency spectrum; can saturate a message channel; the primary source of transmission errors in data circuits

Impulse noise

a sudden, random change in the gain of a circuit resulting in a temporary change in the signal level

Gain hit

a decrease in circuit gain of more than 12 dB lasting longer than 4 ms; characteristics of temporary open-circuit conditions and are generally caused by deep fades on radio facilities or by switching delays

Dropout

sudden, random changes in the phase of a signal; are classified as temporary variations in the phase of a signal lasting longer than 4 ms

Phase hits (slips)

a form of incidental phase modulation-a continuous, uncontrolled variation in the zero crossings of a signal; occurs at a 300 Hz rate or lower and its primary cause is low-frequency ac ripple in power supplies

Phase jitter

52


the presence of one or more continuous, unwanted tones within a message channel

Single-frequency interference

unwanted tones caused by crosstalk or cross modulation between adjacent channels in a transmission system due to system nonlinearities

Spurious tones

occurs in coherent SSBSC systems, such as those using frequency-division multiplexing when the received carrier is not reinserted with the exact phase relationship to the received signal as the transmit carrier possessed

Phase intercept distortion

used to match impedances and to provide isolation between the two directions of signal flow

Hybrid set

used to convert two-wire circuits to four-wire circuits similar to the hybrid coil found in standard telephone sets

Hybrid circuits

eliminate the echo electrically subtracting it from the original signal rather than disabling the amplifier in the return circuit

Echo cancellers

used to eliminate echo Echo suppressors

can be defined as any disturbance created in a communications channel by signals in other communications channels; a potential problem whenever two metallic conductors carrying different signals are located in close proximity to each other; was originally coined to indicate the presence of unwanted speech sounds in a telephone receiver caused by conversations on another telephone circuit

Crosstalk

crosstalk cause by inadequate control of the transfer characteristics or transmittance of networks

Transmittance crosstalk

electromagnetic coupling between two or more physically isolated transmission media;

Coupling crosstalk

crosstalk that occurs at the transmit end of a circuit and travels in the opposite direction as the signal in the disturbing channel

Near-end crosstalk (NEXT)

occurs at the far-end receiver and is energy that travels in the same direction as the signal in the disturbing channel

Far-end crosstalk (FEXT)

referenced to the level on the cable that is being interfered with

dBx for crosstalk

53


CHAPTER 18 : The Public Telephone Network

identifies and connects the subscribers to a suitable transmission path

Switching functions

supply and interpret control and supervisory signals needed to perform the operation

Signaling functions

involves the actual transmission system of a subscriber’s messages and any necessary control signals

Transmission functions

referred to the leased lines designed and configured for their use only

Private-line circuits (dedicated lines)

equipment and facilities that are available to all the public subscribers to the network which includes transmission facilities and telephone switches

Common usage equipment

sometimes called to public telephone companies Service providers

simply the dedicated facility used to connect an instrument at a subscriber’s station to the closest telephone office

Local loop

similar to local loop except trunk circuits used to interconnect two telephone offices; a common usage connection; can be simple as a pair of copper wires twisted together or as sophisticated as an optical fiber cable

Trunk circuit

allows any telephone connected to it to be interconnected to any of the other telephones connected to the exchange without requiring separate cable pairs and telephones for each connection

Telephone exchange

the first telephone exchanges where manual interconnects were accomplished using patchcords and jacks

Switchboards

each telephone line that could have 10 or more subscribers connected to the central office exchange using the same loop

Party line

a programmable matrix that allows circuits to be connected to one another; interconnect input loop or trunk circuits to output loop or trunk circuits

Circuit switch

local exchanges centrally located within the area they serve; can directly interconnect any two

Central offices (CO)

54


subscribers whose local loops are connected to the same local exchange

a telephone call completed within a single local exchange

Intraoffice call (intraswitch call)

calls placed between two stations that are connected to different local exchanges

Interoffice calls

an exchange without any local loops connected to it Tandem office

called switcher’s switch Tandem switch

trunk circuits that terminate in tandem switches Tandem trunks (intermediate trunks)

was established to provide a telephone numbering system for the United States, Mexico, and Canada that would allow any subscriber in North America to direct dial virtually any other subscriber without the assistance of an operator

North American Telephone Numbering Plan (NANP)

allows many subscribers to share a limited number of lines to a central office switch

Concentrator

splits the two directions of signal propagation so that the actual long-distance segment of the route can be accomplished on a four-wire basis

Terminating set (hybrid)

allows a certain degree of route selection when establishing a telephone call

Switching hierarchy

simply a path between two subscribers and is comprised of one or more switches, two local loops, and possibly one or more trunk circuits

Route

an equipment busy signal received by the calling party if a call cannot be completed because the necessary trunks or circuits are not available

Blocking

a local exchange where subscriber loops terminated and received dial tone; end offices interconnected subscriber loop to other subscriber loops and subscriber loops to tandem trunks, interoffice trunks, and toll-connecting trunks

Class 5 end office

provided no operator assistance Class 3 primary center

provide service to geographical regions varying in size from part of a state to all of several states, depending on population density

Class 2 sectional center

the highest-ranking office in the DDD network in terms of the size of the geographical area serves

Class 1 regional center

55


and trunking options available

a global standard for telecommunications defined by the International Telecommunications Union (ITU) Telecommunications Sector (ITU-T); was developed as an alternate and much improved means of transporting signaling information through the public telephone network;

Common channel signaling no. 7 (SS7 or C7)

a telecommunications term that describes the legal boundaries for the responsibility of maintaining equipment and transmission lines; a demarcation point separating two companies

Point-of-presence

allows customers to change to a different service and still keep the same telephone number

Porting

store information about subscriber’s services, routing of special service numbers and calling card validation for fraud protection and provide information necessary for advanced call-processing capabilities

Databases

provides access from one level of the protocol to another level

Primitive

CHAPTER 19 : Cellular Telephone Companies

utilized frequency modulation and were generally assigned a single carrier frequency in the 35 MHz to 45 MHz range that was used by both the mobile unit and the base station

Mobile telephone systems (MTSs) (manual telephone system)

small handsets, easily carried by a person in their pocket or purse

Mobile telephone stations

suggested any radio transmitter, receiver, or transceiver that could be moved while in operation

Mobile

described a relatively small radio unit that was handheld, battery powered, and easily carried by a person moving at walking speed

Portable

similar to two-way mobile radio in that most communications occurs between base stations and mobile units; best describe by pointing out the primary difference between it and two-way mobile radio

Cellular telephone

push-to-talk PTT

56


examples of two-way mobile radio citizen’s band (CB) public land mobile radio

Evolution of Cellular Telephone

July 28, 1945 : Saturday Evening Post, E. K. Jett, then the commissioner of the FCC hinted of a cellular

telephone scheme that he referred to as simply s small zone radio telephone system June 17, 1946 : in St. Louis Missouri, AT&T and Southwestern Bell introduced the first American

commercial mobile radio-telephone service to private customers. In the same year, similar services were offered to 25 major cities throughout the United States

early 1950s : the FCC doubled the number of mobile telephone channels by reducing the bandwidth to

60 kHz per channel1960 : AT&T introduced direct-dialing, full-duplex mobile telephone service with other

performance enhancements1966 : Don Adams, in a television show called Get Smart, unveiled the most famous mobile

telephone to date: the fully mobile shoe phone1968 : AT&T proposed the concept of cellular mobile system to the FCC with the intent of

alleviating the problem of spectrum congestions in the existing mobile telephone system1974 : the FCC allocated an additional 40-MHz bandwidth for cellular telephone service1975 : the FCC granted AT&T the first license to operate a development cellular telephone

service in Chicago1976 : the Bell Mobile Phone service for metropolitan New York City offered only 12 channels

that could serve a maximum of 543 subscribers. FCC granted authorization to the American Radio Telephone Service (ARTS) to install a second developmental system in the Baltimore- Washington, D.C., area

1983 : the FCC allocated 666 30 kHz half-duplex mobile telephone channels to AT&T to form the

first U.S. cellular telephone system called Advanced Mobile Phone System (AMPS)1991 : the first digital cellular services were introduced in several major U.S. cities, enabling a

more efficient utilization of the available bandwidth using voice compressionNovember 17, 1998 : a subsidiary of Motorola Corporation implemented Iridium, a satellite-based wireless

personal communications satellite system (PCSS)

the pattern that fits the cellular concept Honeycomb

defined by its physical size; its physical size varies depending on user density and calling patterns

Cell

the smallest cells used most often in high-density areas such as found in large cities and inside buildings; exhibit milder propagation impairments such as reflections and signal delays

Microcells

57


these is used in well-shielded areas or areas with high levels of interference

Picocells

normally used in center-excited cells (center of the cell)

Omnidirectional antennas

are used in edge- and corner- excited cells (three of the cell’s six vertices)

Sectored directional antennas

the process in which the same set of frequencies (channels) can be allocated to more than one cell, provided the cells are separated by sufficient distance

Frequency reuse

a geographic cellular radio coverage area containing three groups of cells

Clusters

when the area of a cell, or independent component coverage area of a cellular system is further divided, thus creating more cell areas; to increase the channel capacity and improve the availability and reliability of a cellular telephone network

Cell splitting

the point when a cell reaches maximum capacity occurs when the number of subscribers wishing to place a call at any given time equals the number of channels in the cell

Maximum traffic load

decreasing co-channel interference while increasing capacity by using directional antennas

Sectoring

placing two receive antennas; improves reception by effectively providing a larger target for signals radiated from mobile units

Space diversity

divides a group of channels into smaller groupings or segments of mutuality exclusive frequencies; cell sites, which are within the reuse distance, are assigned their own segment of the channel group; a means of avoiding co-channel interference, lowers the capacity of a cell by enabling reuse inside the reuse distance

Segmentation

means of avoiding full-cell splitting where the entire area would otherwise need to be segmented into smaller cells

Dualization

the locations of these radio-frequency transceivers; serves as central control for all users within that cell

Base stations

when mobile unit moves possibly from one company’s service area into another company’s service area

Roaming

the transfer of a mobile unit from one base Handoff (handover)

58


station’s control to another base station’s control

a connection that is momentarily broken during the cell-to-cell transfer

Hard handoff

a flawless handoff; no perceivable interruption of service and normally takes approximately 200 ms which is imperceptible to voice telephone users although the delay may be disruptive when transmitting data

Soft handoff

a protocol aligns with a subprotocol of the SS7 protocol stack that facilitates communications among databases and other network entities; allow mobile units to roam and to perform handoffs of calls already in progress when a mobile unit moves from one cellular system into another without subscriber intervention

IS-41

the process where a mobile unit notifies a serving MTSO of its presence and location through a base station controller

Autonomous registration

operates under the direction o switching center (MTSO); manage each of the radio channels at each site, supervises calls, turns the radio transmitter and receiver on and off, injects data onto the control and voice channels and performs diagnostic tests

Cell-site controller

second part of the base station controllers Base transceiver station (BTS)

also a part of the base station subsystem; used with cellular telephone system voice channels can be either narrowband FM for analog system

Radio transceivers

generally used to connect switching centers to cell sites and to the public telephone network

Four-wire leased lines

governs the way telephone calls are established and is disconnected

Communications protocol

the actual voice channel where mobile users communicate directly with other mobile and wireline subscribers through a base station

User channel

is used for transferring control and diagnostic information between mobile users and a cellular telephone switch through a base station

Control channel

59


CHAPTER 20 Cellular Telephone Systems

a standard cellular telephone service (CTS) initially placed into operation on October 13, 1983; the idea was to eliminate the possibility of a monopoly and provide the advantages that generally accompany a competitive environment

Advanced Mobile Telephone System (AMPS)

a transmission mode that simultaneously transmit in both directions

Duplexing

a 34-bit binary code comprised of a three-digit area code, a three-0digit prefix (exchange number), and a four-digit subscriber (extension) number

Mobile identification number (MIN)

a 32-bit binary code permanently assigned to each mobile unit

Electronic serial number (ESN)

indicates whether the terminal has access to all 832 AMPS channel ; specifies the maximum radiated power for the unit

Four-bit station class mark (SCM)

a 15-bit binary code issued by the FCC to an operating company when it issues it a license to provide AMPS cellular service to an area

System identifier (SID)

combination of cellular telephone networks and the Intelligent Network which is the entity of the SS7 interoffice protocol that distinguishes the physical components of the switching network

Personal Communications System (PCS)

a database that stores information about the user, including home subscription information and what supplementary services the user is subscribed to

Home location register (HLR)

a database that stores information about subscribers in a particular MTSO serving area

Visitor location register (VTR)

a database that stores information pertaining to the identification and type of equipment that exist in the mobile unit

Equipment identification registry (EIR)

allows all calls to pass through the network to the subscriber except for a minimal number of telephone numbers that can be blocked

Available mode

the PCS equivalent to caller ID; the name of the calling party appears on the mobile unit’s display, which allows PCS users to screen calls

Screen mode

60


all calls except those specified by the subscriber are automatically forwarded to a forwarding destination without ringing the subscriber’s handset

Private mode

no calls are allowed to pass through to the subscriber

Unavailable mode

was originally intended to provide a short-term solution to the traffic congestion problem in the AMPS system

Narrowband AMPS (N-AMPS)

used by mobile units to request access to the cellular telephone system; a unidirectional channel specified for transmissions from mobile-to-base units only

RACH

used to transmit information from base stations to specific mobile stations;

SPACH

channels used to carry generic, system-related information; a unidirectional base station-to-mobile unit transmission shared by all mobile units

BCCH

an access method used with standard analog AMPS FDMA

was first used by the military to ensure reliable antijam and to secure communications in a battlefield environment; the fundamental concept is to break a message into fixed-size blocks of data with each block transmitted in sequence except on a different carrier frequency

Frequency-hopping spread spectrum

a high-bit rate pseudorandom code is added to a low-bit rate information signal to generate a high-bit-rate pseudorandom signal closely resembling noise that contains both the original data signal and the pseudorandom code

Direct-sequence spread spectrum

a second-generation cellular telephone system initially developed to solve the fragmentation problems inherent in first-generation cellular telephone system

Global System for Mobile Communications (GSM)

basic parameters of GSM GMSK modulation (Gaussian MSK)

50 MHz bandwidth FDMA/TDMA accessing eight 25-kHz channels

w/in each 200-kHz traffic channel

200 kHz traffic channel 992 full-duplex channels supplementary integrated

services digital network (ISDN) services

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a satellite-based wireless personal communications network designed to permit a wide range of mobile telephone services, including voice, data, networking, facsimile and paging

uses 66 satellites

Iridium

the unique key to the Iridium system and the primary differentiation between Iridium

Satellite cross-links

relay information to the terrestrial gateways and the system control segment located at the earth stations

Feeder links

CHAPTER 21: Introduction to Data Communications and Networking

are systems of interrelated computers and computer equipment and can be as simple as a personal computer connected to a printer or two personal computers connected together through the public telephone network

Data communications network

one of the earliest means of communicating electrically coded information when a proposal submitted to a Scottish magazine suggested running a communications line between villages comprised of 26 parallel wires

1753

Carl Friedrich gauss developed an unusual system based on a five by five matrix representing 25 letters

1833

the first successful data communications system was invented.

1832

the first practical data communications code. Morse code

Morse secured an American patent for the telegraph.

1840

the first telegraph line was established between Baltimore and Washington dc with the first message conveyed over this system.

1844

high speed printers were available 1860

Emile Baudot invented a telegraph multiplexer which allowed signals from up to six different telegraph machines to be transmitted simultaneously over a single wire.

1874

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the telephone was invented by Alexander graham bell

1875

Guglielmo Marconi succeeded in sending radio telegraph messages

1899

the first commercial radio stations carrying voice information were installed

1920

he demonstrated a computing machine sometime in the late 1930s

Konrad Zuis

the first special purpose computer using electromechanical relays for performing logical operations

1940

batch processing systems were replaced by on-line processing systems with terminals connected directly to the computer through serial or parallel communications lines.

1960s

the year introduced microprocessor controlled microcomputers.

1970s

personal computers became an essential item in the home and workplace.

1980s

ATM components routers and switches to connect carrier on global basis

backbone devices to connect all the lans within a large organization

switches and adapters which link desktop computers to high speed atm connection for running multimedia applications

ATM speeds 1.4 Gbps

a digital telecommunications technology that can simultaneously transmit voice and data over the same pair of telephone wires

ISDN

ISDN channels: B-channel (Bearer channel) D channel H channel

used to carry the digital information; build block of the ISDN; 64 kbps

B-channel

used to carry signaling and supervisory information to the network; kpbs (bri) or 64 kbps

D channel

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(pri)

provide for user information at higher bit rates; combination of several b channels

H channel

for business with larger data needs; American 23b + d(t1 = 1.544mbps); European 30b + d (e1= 2.048 mbps)

PRI

150 mbps; for future HDTV projects; h channels Broadband ISDN

CHAPTER 22: Fundamental Concepts of Data Communications

the first fixed-length character code developed for machines rather than for people; named after Emile Baudot, an early pioneer in telegraph printing; a fixed-length source code; all characters are represented in binary and have the same number of symbols (bits)

Baudot Code

the standard character set for source coding the alphanumeric character set that humans understand but computers do not; a seven-bit fixed length character set

United States of America Standard Code for Information Exchange (ASCII)

an eight-bit fixed-length character developed in 1962 by the International Business Machines Corporation (IBM); used almost exclusively with IBM mainframe computers and peripheral equipment

Extended Binary-Coded Decimal Interchange Code (EBCDIC)

are those omnipresent black-and-white striped

stickers that seem to appear on virtually every consumer item in the United States and most of the rest of the world; a series of vertical black bars separated by vertical white bars

Bar codes

has spaces or gaps between characters; each character within the bar code is independent of every other character

Discrete code

does not include spaces between characters Continuous code

stores data in two dimensions in contrast with a conventional linear bar code

2D code

uses an alphanumeric code similar to the ASCII code; consists of 36 unique codes representing the 10 digits and 26 uppercase letters

Code 39 (Code 3 of 9, 3 of 9 Code)

developed sometime in the early 1970s to identify the products of the grocery industry; found on

Universal Product Code (UPC)

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virtually every grocery item from a candy bar to a can of beans

only one bit within a given data string is in error; affects only one character within a message

Single bit error

when two or more non-consecutive bits within a given data string are in error; can affect one or more characters within a message

Multiple bit error

the first fixed length character code developed for machines rather than people

Baudot code

a French postal engineer who developed the Baudot code

Thomas Murray

RTTY is the acronym for _____ Radio teletype

a fixed length source code Baudot code

the standard character set for source coding the alphanumeric character set that humans understand

ASCII

an eight bit fixed length character set developed in 1962 by IBM

EBCDIC

EBCDIC is the acronym for ___ Extended binary coded decimal interchange code

when two or more consecutive bits within a given data string re in error; can affect one or more characters within a message

Burst error

the process of monitoring data transmission and determining when errors have occurred; not to prevent errors from occurring but to prevent undetected errors from occurring

Error detection

duplicating each data unit for the purpose of detecting errors; an effective but rather costly means of detecting errors, especially with long messages

Redundancy

adding bits for the sole purpose of detecting errors Redundancy checking

probably the simplest error-detection scheme Vertical redundancy checking (VRC) (character parity, parity)

own error-detection bit Parity bit

the parity bit is always a 1; useful only when errors occur in a large number of bits

Marking parity

another relatively simple form of redundancy error Checksum

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checking where each character has a numerical value assigned to it; appended to the end of the message

a redundancy error detection scheme that use parity to determine if a transmission error has occurred with a message and is therefore sometimes called message parity

Longitudinal Redundancy Checking (LRC)

the bit sequence for the LRC Block check sequence (BCS) or Frame check sequence (FCS)

probably the most reliable redundancy checking technique for error detection; a convolutional scheme; approximately 99.999% of all transmission errors are detected

Cyclic redundancy checking (CRC)

include enough redundant information with each transmitted message to enable the receiver to determine when an error has occurred

Error-detecting codes

include sufficient extraneous information along with each message to enable the receiver to determine when an error has occurred and which bit is in error

Error-correcting codes

two primary methods used for error-correction: retransmission forward error correction

CHAPTER 23: Data-Link Protocols andData Communications Networks

the primary goal is to give users of a network the tools necessary for setting up the network and performing data flow control

Network architecture

arrangements between people or processes Protocols

a set of rules implementing and governing an orderly exchange of data between layer two devices such as line control units and front-end processors

Data-link protocol

all stations have equal access to the network, but when they have a message to transmit, they must contend with the other stations on the network for access to the transmission medium

Peer-to-peer network

determines which device is transmitting and which is receiving at any point in time

Line discipline

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coordinates the rate at which data are transported over a link and generally provides an acknowledgement mechanism that ensures that data are received at the destination

Flow control

a solicitation sent from the primary to a secondary to determine if the secondary has data to transmit

Poll

how the primary designates a secondary as a destination or recipient of data

Selection

the transmitting station sends one message frame and then waits for an acknowledgement before sending the next message frame

Stop-and-wait flow control

a source station can transmit several frames in succession before receiving an acknowledgement

Sliding window flow control

refers to imaginary receptacles at the source and destination stations with the capacity of holding several frames of data

Sliding window

interpret a frame of data as a group of successive bits combined into predefined patterns of fixed length usually eight bits

Character-oriented protocols

a discipline for serial-by-bit information transfer over a data communications channel

Bit-oriented protocol

are relatively simple, character-oriented generally used on two-point networks using asynchronous data and asynchronous modems

Asynchronous data-link protocols

remote stations can have more than one PC or printer

Synchronous data-link protocols

group of computers, printers, and other digital devices

Cluster

a synchronous character-oriented data-link protocol developed by IBM; sometimes called bisync or bisynchronous communications

Binary synchronous communications (BSC)

a synchronous bit-oriented protocol developed in the 1970s by the IBM for use in system network architecture environment

Synchronous data-link control (SLDC)

an information field is not allowed; cannot be used to transfer numbered information

Supervisory frame

causes all previously set functions to be cleared by the secondary

Clear

causes the secondary to turn on or turn off Beacon test

causes the addressed secondary station to place Monitor mode

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itself into the monitor mode

causes a secondary station to loop its transmission directly to its receiver input

Wrap

make a receiver transparent to all data located Transparency

a switched data communications network similar to the public telephone network except it is designed for transferring data only

Public switched data network (PDN or PSDN)

involves dividing data messages into small bundles of information and transmitting them through communications networks to their intended destinations using computer-controlled switches

Packet switching

logically equivalent to a two-point dedicated private-line circuit except slower

Permanent virtual circuit (PVC)

users send small packets of data into the network Datagram (DG)

the integrating of a wide range of services into a single multipurpose network; a network that proposes to interconnect an unlimited number of independent users through a common communication network

Integrated service digital network (ISDN)

provides the most economical and effective means of handling local data communication needs

Local area network (LAN)

the time it takes a signal to travel from a source to a destination

Propagation delay

CHAPTER 24: Microwave Radio Communications and System Gain

described as electromagnetic waves with frequencies that range from approximately 500 MHz to 300 GHz or more

Microwave

systems are those used to carry information for relatively long distances

Long-haul microwave systems

propagate signals through Earth’s atmosphere between transmitters and receivers often located on top of towers spaced about 15 miles to 30 miles apart

Microwave radios

the composite signal that modulates the FM carrier Baseband

a preemphasis network precedes the FM deviator; Microwave transmitter

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provides an artificial boost in amplitude to the higher baseband frequencies

a receiver and a transmitter placed back to back or in tandem with the system

Microwave repeaters

another name for local oscillator and is considerably lower in frequency than either the received or the transmitted radio frequencies

Shift oscillator

the reduction in signal strength Radio fade

it suggests that there is more than one transmission path or method of transmission available between a transmitter and a receiver; used to increase the reliability of the system by increasing its availability

Diversity

simply modulating two different RF carrier frequencies with the same IF intelligence, then transmitting both RF signals to a given destination

Frequency diversity

the output of a transmitter is fed to two or more antennas that are physically separated by an appreciable number of wavelengths

Space diversity

a single RF carrier is propagated with two different electromagnetic polarizations

Polarization diversity

using more than one receiver for a single radio-frequency channel

Receiver diversity

it combines frequency, space, polarization and receiver diversity into one system

Quad diversity

somewhat specialized form of diversity that consists of a standard frequency-diversity path where the two transmitter/receiver pairs at one end of the path are separated from each other and connected to different antennas that are vertically separated as in space diversity

Hybrid diversity

provide protection for a much larger section of the communications system that generally includes several repeaters spanning a distance of 100 miles or more

Protection switching arrangement

two types of protection switching arrangement: hot standby diversity

each working radio channel has a dedicated backup or spare channel

Hot standby protection

a single backup channel is made available to as many as 11 working channels

Diversity protection

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points in the system where baseband signals either originate or terminate

Terminals

points in a system where baseband signals may be reconfigured or where RF carriers are simply repeated or amplified

Repeater stations

a balanced modulator that when used in conjunction with a microwave generator, power amplifier, and bandpass filter, up-converts the IF carrier to an RF carrier and amplifies the RF to the desired output power

Transmit modulator (transmod)

a unidirectional device often made from a ferrite material; used in conjunction with a channel-combining network to prevent the output of one transmitter from interfering with the output of another transmitter

Isolator

this occurs when three stations are placed in a geographical straight line in the system

Multihop interference

preventing the power that leaks out the back and sides of a transmit antenna from interfering with the signal entering the input of a nearby receive antenna

Ring around

the line-of-sight path directly between the transmit and receive antennas

Free-space path

the portion of the transmit signal that is reflected off Earth’s surface and captured by the receive antenna

Ground-reflected wave

consists of the electric and magnetic fields associated with the currents induced in Earth’s surface

Surface wave

the portion of the transmit signal that is returned back to Earth’s surface by the ionized layers of Earth’s atmosphere

Sky wave

often defined as the loss incurred by an electromagnetic wave as it propagates in a straight line through a vacuum with no absorption or reflection of energy from a nearby objects

Free-space path loss

a phenomena where in no electromagnetic is actually lost or dissipated – it merely spreads out as it propagates away from the source resulting in lower relative power densities

Spreading loss

the reduction in receive signal level; reduction in signal strength at the input to a receiver; it applies

Fading

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to propagation variables in the physical radio path that affect changes in the path loss between transmit and receive antennas

the difference between the nominal output power of a transmitter and the minimum input power to a receiver necessary to achieve satisfactory performance; must be greater than or equal to the sum of all gains and losses incurred by a signal as it propagates from a transmitter to a receiver

System gain

essentially a fudge factor included in system gain equations that considers the nonideal and less predictable characteristics of radiowave propagation, such as multipath propagation and terrain sensitivity; these characteristics cause temporary, abnormal atmospheric conditions

Fade margin (link margin)

the minimum wideband carrier power at the input to a receiver that will provide a usable baseband output

Receiver threshold (receiver sensitivity)

simply a ratio of input signal-to-noise ratio to output signal-to-noise ratio

Noise factor

indicates how much the signal-to-noise ratio deteriorates as a waveform propagates from the input of a circuit

Noise figure

CHAPTER 25 : Satellite Communications

in astronomical terms, a celestial body that orbits around a planet; in aerospace terms, a space vehicle launched by humans and orbits Earth or another celestial body

Satellites

a microwave repeater in the sky that consists of a diverse combination of one or more of the following: receiver, transmitter, amplifier, regenerator, filter, onboard computer, multiplexer, demultiplexer, antenna, waveguide and about nay other electronic communications circuit ever developed

Communications satellite

called a transponder Satellite radio repeater

consists of one or more satellite space vehicles, a ground-based station to control the operation of the system and a user network of earth stations that provides the interface facilities for the transmission and reception of terrestrial communications traffic

Satellite system

includes control mechanisms that support the payload operation

Bus

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the actual user information conveyed through the system

Payload

a continuously transmitted unmodulated carrier that an earth station can lock on to and use to determine the exact location of a satellite so the earth station can align its antennas

Beacon

accomplished the first transatlantic transmission Echo

meaning lightning Molniya

Kepler’s laws: the planets move in ellipses with the sun at one focus

the line joinining the sun and a planet sweeps out equal areas in equal intervals of time (laws of areas)

the square of the time of revolution of a planet divided by the cube of its mean distance from the sun gives a number that is the same for all planets (harmonic law)

closest approach to the earth Perigee

farthest point from earth Apogee

rotate around the Earth in an elliptical or circular pattern

Orbital satellites (nonsynchronous)

the orbit if the satellite is orbiting in the same direction as Earth’s rotation (counterclockwise) and at an angular greater than that of earth

Prograde or posigrade orbit

the orbit if the satellite is orbiting in the opposite direction of Earth’s rotation or in the same direction with an angular velocity less than that of Earth

Retrograde orbit

a system utilizing a 66-satellite constellation orbiting approximately 480 miles above Earth’s surface; the main advantage is that the path loss between earth stations and space vehicles is much lower than for satellites revolving in medium- or high-altitude orbits

Low Earth Orbit

operate in the 1.2 GHz to 1.66 GHz frequency band and orbit between 6000 miles and 12000 miles above the Earth

Medium Earth Orbit

high-altitude earth-orbit satellites operating primarily in the 2 GHz to 18 GHz frequency

Geosynchronous satellites

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spectrum with orbits 22 300 miles above the Earth’s surface

the line joining the perigee and apogee the center of Earth

Major Axis (line of apsides)

the line perpendicular to the major axis and halfway between the perigee and apogee

Minor axis

half the distance of the minor axis Semiminor axis

all satellites rotate around Earth in an orbit that forms a plane that passes through the center of gravity of Earth

Geocenter

are virtually all orbits except those that travel directly above the equator or directly over the North and South Poles

Inclined Orbits

the angle between the Earth’s equatorial plane and the orbital plane of a satellite measured counterclockwise at the point in the orbit where it crosses the equatorial plane traveling from south to north

Angle of inclination

traveling from south to north Ascending node

the point where a polar or inclined orbit crosses the equatorial plane traveling from north to south

Descending node

the line joining the ascending an descending nodes through the center of Earth

Line of nodes

when the satellite rotates in an orbit directly above the equator, usually in a circular path

Equatorial orbit

when the satellite rotates in a path that takes it over the North and South poles in an orbit perpendicular to the equatorial plane

Polar orbit

causing elliptical orbits to rotate in a manner that causes the apogee and perigee to move around the Earth

Rotation of the line of apsides

satellites appear to remain in a fixed location above one spot on earth’s surface

Geosynchronous (stationary or geostationary)

the process of maneuvering a satellite within a preassigned window

Station keeping

the circumference of a geosynchronous orbit 264 790 km

the velocity of a geosynchronous satellite 6840 mph

sometimes referred to geosynchronous earth orbit Clarke orbit or Clarke belt

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direction of maximum gain of an earth station antenna

Boresight

azimuth and elevation angle are jointly referred to __________

Look angles

a point on the surface below the satellite Subsatellite point (SSP)

the vertical angle formed between the direction of travel of an electromagnetic wave radiated from an earth station antenna pointing directly toward a satellite and the horizontal plane

Angle of elevation

the horizontal angular distance from a reference direction either the southern or northern most point of the horizon

Azimuth

defined as the horizontal pointing angle of an earth station antenna

Azimuth angle

determine the farthest satellite away that can be seen looking east or west of the earth station’s longitude

Line-of-sight limits

uses the angular momentum of its spinning body to provide roll and yaw stabilization

Spinner satellite

the body remains fixed relative to Earth’s surface, while an internal subsystem provides roll and yaw stabilization

Three-axis stabilizer satellites

the geographical representation of a satellite antenna’s radiation pattern; the area on Earth’s surface that the satellite can receive from or transmit to

Footprint (footprint map)

the smallest beams; concentrate their power to very small geographical areas and, therefore, typically have proportionately higher EIRPs than those targeting much larger areas because a given output power can be more concentrated

Spot beams

typically target up to 20% of the Earth’s surface and, therefore, have EIRPs that are 3 dB or 50% lower than those transmitted by spot beams that typically cover only 10% of the Earth’s surface

Hemispherical downlink antennas

have a beamwidth of approximately 42% of Earth’s surface which is the maximum view of any one geosynchronous satellite

Earth coverage

increasing the size of an antenna, the beamwidth of the antenna is also reduced thus, different beams of the same frequency can be directed to different geographical areas of Earth

Frequency reuse

consists of an input bandlimiting device (BPF), an Satellite transponder

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input low-noise amplifier (LNA), a frequency translator, a low-level power amplifier, and an output bandpass filter

used when it is necessary to communicate between satellites

Cross-links or intersatellite links (ISLs)

high power amplifiers used in earth station transmitters and the traveling-wave tubes typically used in a satellite transponders

Nonlinear devices

the amount the output level is backed off from rated levels equivalent to a loss

Back-off loss

defined as an equivalent transmit power Effective isotropic radiated power (EIRP)

a hypothetical value that can be calculated but cannot be measured; often used rather than noise figure because it is more accurate method of expressing the noise contributed by a device or a receiver when evaluating its performance

Equivalent noise temperature

the noise power normalized to a 1-Hz band width, or the noise power present in a 1-Hz bandwidth

Noise density

the average wideband carrier power-to-noise density ratio

Carrier-to-noise density ratio

the combines power of the carrier and its associated sidebands

Wideband carrier power

the thermal noise present in a normalized 1-Hz bandwidth

Noise density

CHAPTER 26: Satellite Multiple Accessing Arrangements

sometimes called multiple destination because the transmission from each earth station are received by all the other earth stations in the system

Multiple accessing

method of assigning adjacent channels different electromagnetic polarization

Frequency reuse

an Eskimo word meaning “little brother” Anik

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a method required when three or more earth stations wish to communicate with each other

Multiple accessing

sometimes called to multiple accessing because the transmissions from each earth station are received by all the other earth stations in the system

Multiple destination

when it is used, a given number of the available voice-band channels from each other station are assigned a dedicated station

Preassignment

voice-channels are assigned on an as-needed basis; provides more versatility and more efficient use of the available frequency spectrum

Demand assignment

each earth station’s transmissions are assigned

specific uplink and downlink frequency bands within an allotted satellite; transmissions are separated in the frequency domain

FDMA

each earth station transmits a short burst of information during a specific time slot (epoch); transmissions are separated in the time domain; the entire transponder bandwidth and power are used for each transmission but for only a prescribed interval of time

TDMA

the entire satellite transponder bandwidth is used by all stations on a continuous basis; signal separation is accomplished with envelope encryption/decryption techniques

CDMA

an alternate channel allocation scheme Demand-assignment, multiple access (DAMA)

an acronym for single-channel-per-carrier PCM multiple-access demand-assignment equipment

SPADE

a time-division-multiplexed transmission that is frequency-division multiplexed into the spectrum below the QPSK-encoded voice-band channels with a 160 KHz bandwidth

Common signaling channel (CSC)

called when each stations can transmit only during their specified time slot although the incoming voice-band signals are continuous

Store-and-forward system

a unique binary word Chip code

produced when a bipolar data-modulated signal is linearly multiplied by the spreading signal in a special balanced modulator

Direct-sequence spread spectrum (DS-SS)

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a form of CDMA where a digital code is used to continually change the frequency of the carrier

Frequency hopping

there can be more TCs assigned than there are SCs Channel compression

a phenomenon when speech energy is detected on a TC and there is no SC to assign it to

Competitive clipping

a form of analog channel compression that has been used for suboceanic cables for many years

Time-assignment speech interpolation (TASI)

can be defined as the art or science of plotting, ascertaining, or directing the course of movements; knowing where you are and being able to find your way around

Navigation

the most ancient and rudimentary method of navigation; is simply continuing to travel about until you reach your destination

Wandering

direction and distance are determined from precisely timed sightings of celestial bodies including the stars and moon; a primitive technique that dates back thousand of years

Celestial navigation

another rudimentary method of navigation; fixing a position and direction with respect to familiar, significant landmarks, such as railroad tracks, water towers, barns, mountain peaks and bodies of water

Piloting

a navigation technique that determines position by extrapolating a series of measured velocity increments used quite successfully by Charles Lindbergh in 1927 during his historic 33 hour transatlantic journey and quite unsuccessfully by Amelia Earhart in 1937 during her attempt to make first around-the-world flight

Dead reckoning

the most accurate navigation technique; position is determined by measuring the travel time of an electromagnetic wave as it moves from a transmitter to a receiver

Radio or electronic navigation

consist of 24 operational satellites revolving around Earth in six orbital planes approximately 60° apart with four satellites in each plane; there are 21 working satellites and three satellites reserved as spaces

Space segment

this unique number is used to encrypt the signal from that satellite

Pseudorandom noise (PRN) code

a term generally associated with a table showing the position of a heavenly body on a number of dates in a regular sequence, in essence, an

Ephemeris

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astronomical almanac

the Navstar control segment which includes all the fixed-location ground-based monitor stations located throughout the world a master control station (MCS), and uplink transmitters

Operational control system (OCS)

makes GPS even more accurate; works by canceling out most of the natural and man-made errors that creep into normal GPS measurements

Differential GPS

-end-

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tomasi outlined

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