Glossary

AI-1

Appendix I

GLOSSARY AMPLITUDE—Used to represent values of electrical current or voltage. The greater its height, the greater the value it represents. AMPLITUDE MODULATION—Any method of varying the amplitude of an electromagnetic carrier frequency in accordance with the intelligence to be transmitted ANGLE MODULATION—Modulation in which the angle of a sine-wave carrier is varied by a modulating wave. AVERAGE POWER—The peak power value averaged over the pulse-repetition time. BANDWIDTH—The section of the frequency spectrum that specific signals occupy.

BASE-INJECTION MODULATOR—Similar to control-grid modulator. Gain of a transistor is varied by changing the bias on its base. BLOCKED-GRID KEYING—A method of keying in which the bias is varied to turn plate current on and off. BUFFER—A voltage amplifier used between the oscillator and power amplifier. CARBON MICROPHONE—Microphone in which sound waves vary the resistance of a pile of carbon granules. May be single-button or double-button. CARRIER FREQUENCY—The assigned transmitter frequency. CARRIER—Radio-frequency sine wave.

CATHODE KEYING—A system in which the cathode circuit is interrupted so that neither grid current nor plate current can flow. CATHODE MODULATOR—Voltage on the cathode is varied to produce the modulation envelope. CHANNEL—Carrier frequency assignment usually with a fixed bandwidth. COLLECTOR-INJECTION MODULATOR—Transistor equivalent of plate modulator. Modulating voltage is applied to collector circuit. COMMON-BASE DETECTOR—An amplifying detector where detection occurs in emitter-base junction and amplification occurs at the output of the collector junction.

COMMON-EMITTER DETECTOR—Often used in receivers to supply detected and amplified output. The emitter-base junction acts as the detector. COMPLEX WAVE—A wave composed of two or more parts. CONTINUOUS-WAVE KEYING—The "on-off" keying of a carrier. AI-2 CONTROL-GRID MODULATOR—Uses a variation of grid bias to vary the instantaneous plate voltage and current. The modulating signal is applied to the control grid. CONVERSION—The process of changing ppm or pcm to pdm or pam to make them easier to demodulate. CRYSTAL MICROPHONE—Uses the piezo-electric effect of crystalline materials to generate a voltage from sound waves.

CUSPS—Sharp phase reversals. CW DEMODULATOR—A circuit that detects the presence of rf oscillations and converts them into a useful form. CYCLE—360 degree rotation of a vector generating a sine wave. DEMODULATION—The removal of intelligence from a transmission medium. DEMODULATION or DETECTION—The process of re-creating original modulating- frequency intelligence from the rf carrier. DEMODULATOR or DETECTOR—A circuit in which demodulation or restoration of the original intelligence is achieved. DIODE DETECTOR—A simple type of crystal receiver.

DUTY CYCLE—The ratio of working time to total time for intermittently operated devices. DYNAMIC MICROPHONE—A device in which sound waves move a coil of fine wire that is mounted on the back of a diaphragm and located in the magnetic field of a permanent magnet. EMITTER-INJECTION MODULATOR—The transistor equivalent of the cathode modulator. The gain is varied by changing the voltage on the emitter. FIDELITY—The ability to faithfully re-produce the input in the output. FINAL POWER AMPLIFIER (fpa)—The final stage of amplification in a transmitter.

FIXED SPARK GAP—A device used to discharge the pulse-forming network. A trigger pulse ionizes the air between two contacts to initiate the discharge. FOSTER-SEELEY DISCRIMINATOR—A circuit that uses a double-tuned rf transformer to convert frequency variations in the received fm signal to amplitude variations. Also known as a phase-shift discriminator. FREQUENCY DEVIATION—The amount the frequency departs from the carrier frequency. FREQUENCY MODULATION (fm)—Angle modulation in which the modulating signal causes the carrier frequency to vary. The amplitude of the modulating signal determines how far the frequency changes and the frequency of the modulating signal determines how fast the frequency changes.

FREQUENCY MULTIPLIERS—Special rf power amplifiers that multiply the input frequency. AI-3 FREQUENCY—The rate at which the vector that generates a sine wave rotates. FREQUENCY-SHIFT KEYING (fsk)—Frequency modulation somewhat similar to continuous-wave (cw) keying in AM transmitters. The carrier is shifted between two differing frequencies by opening and closing a key. GATED-BEAM DETECTOR—An fm demodulator that uses a special gated-beam tube to limit, detect, and amplify the received fm signal. Also known as a quadrature detector.

HARMONIC FREQUENCIES—Integral multiples of a fundamental frequency HETERODYNE DETECTION—The use of an af voltage to distinguish between available signals. The incoming cw signal is mixed with locally generated oscillations to give an af output. HETERODYNING—Mixing two frequencies across a nonlinear impedance. HIGH-LEVEL MODULATION—Modulation produced in the plate circuit of the last radio stage of the system. INSTANTANEOUS AMPLITUDE—The amplitude at any given point along a sine wave at a specific instant in time. INTERMEDIATE POWER AMPLIFIER (ipa)—The amplifier between the oscillator and final power amplifier.

KEY CLICKS—Interference in the form of "clicks" or "thumps" caused by the sudden application or removal of power. KEY-CLICK FILTERS—Filters used in keying systems to prevent key-click interference. KEYING RELAYS—Relays used in high- power transmitters where the ordinary hand key cannot accommodate the plate current without excessive arcing. LINEAR IMPEDANCE—An impedance in which a change in current through a device changes in direct proportion to the voltage applied to the device. LOW-LEVEL MODULATION—Modulation produced in an earlier stage than the final.

LOW-PASS FILTER—A method of demodulating pdm by averaging the voltage over pulse and no-pulse time. LOWER SIDEBAND—All difference frequencies below that of the carrier. MACHINE KEYING—A method of cw keying using punched tape or other mechanical means to key a transmitter. MAGNETIC MICROPHONE—A microphone in which the sound waves vibrate a moving armature. The armature consists of a coil wound on the armature and located between the pole pieces of a permanent magnet. The armature is mechanically linked to the diaphragm.

MARK—An interval during which a signal is present. Also the presence of an rf signal in cw keying. The key-closed condition (presence of data) in communications systems. AI-4 MASTER OSCILLATOR POWER AMPLIFIER (MOPA)—A transmitter in which the oscillator is isolated from the antenna by a power amplifier. MICROPHONE—An energy converter that changes sound energy into electrical energy. MODULATED WAVE—A complex wave consisting of a carrier and a modulating wave that is transmitted through space. MODULATING WAVE—An information wave representing intelligence.

MODULATION FACTOR (M)—An indication of relative magnitudes of the rf carrier and the audio-modulating signal. MODULATION INDEX—The ratio of frequency deviation to the frequency of the modulating signal. MODULATION—The ability to impress intelligence upon a transmission medium, such as radio waves. MODULATOR—The last audio stage in which intelligence is applied to the rf stage to modulate the carrier. MULTIPLICATION FACTOR—The number of times an input frequency is multiplied. MULTIVIBRATOR MODULATOR—An astable multivibrator used to provide frequency modulation by inserting the modulating af voltage in series with the base-return of the multivibrator transistors.

NEGATIVE ALTERNATION—That part of a sine wave that is below the reference level. NONLINEAR DEVICE—A device in which the output does not rise and fall directly with the input. NONLINEAR IMPEDANCE—An impedance in which the resulting current through the device is not proportional to the applied voltage. OVERMODULATION—A condition that exists when the peaks of the modulating signal are limited. PEAK AMPLITUDE—The maximum value above or below the reference line. PEAK DETECTION—Detection that uses the amplitude of pam or the duration of pdm to charge a holding capacitor and restore the original waveform.

PEAK POWER—The maximum value of the transmitted pulse. PERCENT OF MODULATION—The degree of modulation defined in terms of the maximum permissible amount of modulation. PERIOD—The duration of a waveform. PHASE MODULATION (pm)—Angle modulation in which the phase of the carrier is controlled by the modulating waveform. The amplitude of the modulating wave determines the amount of phase shift and the frequency of the modulation determines how often the phase shifts. AI-5 PHASE or PHASE ANGLE—The angle that exists between the starting point of a vector and its position at that instant. An indication of how much of a cycle has been completed at any given instant in time.

PHASE-SHIFT DISCRIMINATOR—See Foster-Seeley discriminator. PHASE-SHIFT KEYING—Similar to ON-OFF cw keying in AM systems and frequency-shift keying in fm systems. Each time a mark is received, the phase is reversed. No phase reversal takes place when a space is received. PLATE KEYING—A keying system in which the plate supply is interrupted. PLATE MODULATOR—An electron-tube modulator in which the modulating voltage is applied to the plate circuit of the tube. POSITIVE ALTERNATION—That part of a sine wave that is above the reference line.

PULSE DURATION (pd)—The period of time during which a pulse is present. PULSE MODULATION—A form of modulation in which one of the characteristics of a pulse train is varied. PULSE WIDTH (pw)—The period of time during which a pulse occurs. PULSE—A surge of plate current that occurs when a tube is momentarily saturated. PULSE-AMPLITUDE MODULATION (pam)—Pulse modulation in which the amplitude of the pulses is varied by the modulating signal. PULSE-CODE MODULATION (pcm)—A modulation system in which the standard values of a quantized wave are indicated by a series of coded pulses.

PULSE-DURATION MODULATION (pdm)—Pulse modulation in which the time duration of the pulses is changed by the modulating signal. PULSE-FORMING NETWORK (pfn)—A circuit used for storing energy. Essentially a short section of artificial transmission line. PULSE-FREQUENCY MODULATION (pfm)—Pulse modulation in which the modulating voltage varies the repetition rate of a pulse train. PULSE-POSITION MODULATION (ppm)—Pulse modulation in which the position of the pulses is varied by the modulating voltage. PULSE-REPETITION FREQUENCY—The rate, in pulses per second, at which the pulses occur.

PULSE-REPETITION TIME (prt)—The total time for one complete pulse cycle of operation (rest time plus pulse width). PULSE-TIME MODULATION (ptm)—Pulse modulation that varies one of the time characteristics of a pulse train (pwm, pdm, ppm, and pfm). PULSE-WIDTH MODULATION (pwm)—Pulse modulation in which the duration of the pulses is varied by the modulating voltage. AI-6 PULSING—Allowing oscillations to occur for a specific period of time only during selected intervals. QUANTIZED WAVE—A wave created by arbitrarily dividing the entire range of amplitude (or frequency, or phase) values of an analog wave into a series of standard values. Each sample takes the standard value nearest its actual value when modulated.

QUANTIZING NOISE—A distortion introduced by quantizing the signal. RADAR DETECTOR—A detector which, in its simplest form, only needs to be capable of producing an output when rf energy (reflected from a target) is present at its input. RATIO DETECTOR—A detector that uses a double-tuned transformer to convert the instantaneous frequency variations of the fm input signal to instantaneous amplitude variations. RATIO OF TRANSMITTED POWERS—The power ratio ( fsk verses AM) that expresses the overall improvement of fsk transmission when compared to AM under rapid-fading and high-noise conditions.

REACTANCE TUBE—A tube connected in parallel with the tank circuit of an oscillator. Provides a signal that will either lag or lead the signal produced by the tank. REACTANCE-TUBE MODULATOR—An fm modulator that uses a reactance tube in parallel with the oscillator tank circuit. REGENERATIVE DETECTOR—A detector circuit that produces its own oscillations, heterodynes them with an incoming signal, and detects them. REST FREQUENCY—The carrier frequency during the constant-amplitude portions of a phase modulation signal.

REST TIME (rt)—The time when there is no pulse or nonpulse. ROTARY GAP—Similar to a mechanically driven switch. Used to discharge a pulse-forming network. SENSITIVITY OF A MICROPHONE—Efficiency of a microphone. Describes micro- phone power delivered to a matched-impedance load as compared to the sound level being converted. Usually expressed in terms of the electrical power level. SERIES-DIODE DETECTOR—The semiconductor diode in series with the input voltage and the load impedance. Sometimes called a voltage-diode detector.

SHUNT—Means the same as parallel or to place in parallel with other components. SHUNT-DIODE DETECTOR—A diode detector in which the diode is in parallel with the input voltage and the load impedance. Also known as a current detector because it operates with smaller input levels. SIGNAL DISTORTION—Any unwanted change to the signal. SIGNIFICANT SIDEBANDS—Those sidebands with significantly large amplitude. AI-7 SINE WAVE—The basic synchronous alternating waveform for all complex waveforms. SLOPE DETECTOR—A tank circuit tuned to a frequency, either slightly above or below an fm carrier frequency, that is used to detect intelligence.

SPACE—Absence of an rf signal in cw keying. Key-open condition or lack of data in communications systems. Also a period of no signal. SPARK-GAP MODULATOR—Modulator consists of a circuit for storing energy, a circuit for rapidly discharging the storage circuit (spark gap), a pulse transformer, and a power source. SPECTRUM ANALYSIS—The display of electromagnetic energy arranged according to wavelength or frequency. SPLATTER—Unwanted sideband frequencies that are generated from overmodulation. THYRATRON MODULATOR—An electronic switch that requires a low potential to turn it on.

TRANSMISSION MEDIUM—A means of transferring intelligence from point to point. Can be described as light, smoke, sound, wirelines, or radio-frequency waves. UPPER SIDEBAND—All of the sum frequencies above the carrier. VARACTOR—A diode, or pn junction, that is designed to have a certain amount of capacitance between junctions. VARACTOR FM MODULATOR—An fm modulator which uses avoltage-variable capacitordiode (varactor). VOLTAGE-DIODE DETECTOR—Series detector in which the crystal is in series with the input voltage and the load impedance.

VECTOR—Mathematical method of showing both magnitude and direction. WAVELENGTH—The physical dimension of a sine wave. INDEX-1

Module 12 Index

A Ac applied to linear and nonlinear impedances, 1-18 AM demodulation, 3-6 to 3-10 AM transmitter principles, 1-42 Amplitude, 1-7 Amplitude modulation, 1-1 to 1-62 amplitude-modulated systems, 1-26 AM transmitter principles, 1-42 amplitude modulation, 1-36 continuous wave (cw), 1-26 modulation systems, 1-54 heterodyning, 1-10 ac applied to linear and nonlinear impedances, 1-18 combined linear and nonlinear impedance, 1-17 linear impedance, 1-11 nonlinear impedance, 1-16 spectrum analysis, 1-25 two sine-wave generators and a combination of linear and nonlinear impedances, 1-22 two sine-wave generators in linear circuits, 1-20 typical heterodyning circuit, 1-25 introduction to modulation principles, 1-1 sine-wave characteristics, 1-2 amplitude, 1-7 frequency, 1-7 generation of sine waves, 1-3 period, 1-7 phase, 1-7 wavelength, 1-8 summary, 1-62 Angle and pulse modulation, 2-1 angle modulation, 2-2 basic modulator, 2-25 frequency-modulation systems, 2-2 frequency-shift keying, 2-2 modulation index, 2-23 phase modulation, 2-21 phase-shift keying, 2-26 Angle and pulse modulation—Continued introduction, 2-1 pulse modulation, 2-29 characteristics, 2-29 communications pulse modulators, 2-40 pulse timing, 2-32 radar modulation, 2-38 spark-gap modulator, 2-38 thyratron modulator, 2-39 summary, 2-52 B Basic modulator, 2-25 C Characteristics, pulse modulation, 2-29 Combined linear and nonlinear impedance, 1-17 Common-base detector, 3-10 Common-emitter detectors, 3-9 Communications pulse modulators, 2-40 Continuous wave (cw), 1-26 Continuous-wave demodulation, 3-2 Conversion, 3-25 D Demodulation, 3-1 AM demodulation, 3-6 common-base detector, 3-10 common-emitter detectors, 3-9 diode detectors, 3-6 continuous-wave demodulation, 3-2 heterodyne detection, 3-3 regenerative detector, 3-5 fm demodulation, 3-10 Foster-Seeley discriminator, 3-12 gated-beam detector, 3-17 ratio detector, 3-15 slope detection, 3-11 introduction, 3-1 INDEX-2 Demodulation—Continued phase demodulation, 3-21 pulse demodulation, 3-23 conversion, 3-25 low-pass filter, 3-24 peak detection, 3-23 summary, 3-28 Diode detectors, 3-6 F Fm demodulation, 3-10 Foster-Seeley discriminator, 3-12 Frequency, 1-7 Frequency-modulation systems, 2-2 Frequency-shift keying, 2-2 G Gated-beam detector, 3-17 Generation of sine waves, 1-3 Glossary, AI-1 to AI-7 H Heterodyne detection, 3-3 Heterodyning, 1-10 L Learning objectives, 1-1, 2-1, 3-1 Linear impedance, 1-11 Low-pass filter, 3-24 M Modulation index, 2-23 Modulation principles, introduction to, 1-1 Modulation systems, 1-54 N Nonlinear impedance, 1-16 P Peak detection, 3-23 Period, 1-7 Phase, 1-7 Phase demodulation, 3-21 Phase modulation, 2-21 Phase-shift keying, 2-26 Pulse and angle modulation, 2-1 Pulse demodulation, 3-23 R Radar modulation, 2-38 Ratio detector, 3-15 Regenerative detector, 3-5 S Sine-wave characteristics, 1-2 Slope detection, 3-11 Spark-gap modulator, 2-38 Spectrum analysis, 1-25 T Thyratron modulator, 2-39 Timing, pulse, 2-32 Two sine-wave generators and a combination of linear and nonlinear impedances, 1-22 Two sine-wave generators, in linear circuits, 1-20 Typical heterodyning circuit, 1-25 W Wavelength, 1-8