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Glossary
a.f.c. - Automatic frequency control: (1) control of the frequency of the
local oscillator in a superheterodyne to keep the receiver in tune with a desired
station; (2) control of the frequency of the horizontal oscillator in a television
receiver to keep the horizontal deflection in step with the horizontal deflection
at the television studio and thus to keep the picture steady horizontally.
a.g.c. - Automatic gain control, control of the amplification of an amplifier
so that its output is approximately constant in spite of variations in the input
signal; especially such control in television receivers to reduce variations in
picture contrast produced by variations in r.f. signal strength.
a.v.c. - Automatic volume control (a.g.c. used in radio receivers to reduce
variations in sound volume produced by variations in r.f. signal strength).
choke - An inductance used especially to present a high impedance to a
wide range of frequencies. Filter chokes are used in rectifier-type power supplies
to remove from the d.c. output hum components equal to the power line frequency
and its harmonics; audio-frequency chokes are used in audio amplifiers and radio-frequency
chokes are used in r.f. and i.f. amplifiers, to present a high impedance load to
a vacuum tube or to block unwanted signals.
crystal - 1. Rectifying crystal, one which passes electric current more
easily in one direction than in the other and thus can be used to change alternating
current to pulsating direct current; made of such materials as germanium, silicon,
copper oxide, galena, and carborundum. 2. Piezo-electric crystal, one which transforms
mechanical energy to electrical and vice versa. Such crystals, made of Rochelle
salt or barium titanate, are used in microphones and phonograph pickups. When cut
to a certain size and shape, a piezoelectric crystal, usually made of quartz, can
be used as a resonant circuit, to control the frequency of an oscillator or as a
frequency-selective filter.
decibel - A measure of the ratio between two power levels or of a power
level with respect to a designated reference level. Basically, the number of decibels
is ten times the logarithm of a power ratio. One decibel is approximately the smallest
difference in sound power which can be detected by the average human ear.
db of feedback - The number of decibels by which inverse feedback in an
amplifier reduces its over-all gain and distortion.
detector - A circuit used to recover an audio or video signal from a modulated
radio signal.
electrolytic capacitor - A type of capacitor in which the dielectric or
insulator is a thin film of oxide deposited on one aluminum or tantalum plate and
an electrolyte is used between the insulator and the other plate. This type of capacitor
provides a larger capacitance in a given volume than any other type. However, except
for special a.c. electrolytics, this type can be used only in circuits where voltage
of constant polarity is applied to it.
elevator - Control surface of an aircraft which regulates its pitch attitude
(level, climbing, or diving).
feedback - Returning part of the output of an amplifier stage to the input
of the same or a previous stage. Negative or inverse (out-of-phase) feedback decreases
the gain and distortion of the amplifier; positive (in-phase) feedback increases
gain and distortion and may produce oscillation.
frequency response - The relative ability of an amplifier, loudspeaker,
or other device to respond to different frequencies.
glow plug - A type of internal- combustion engine used in models, in which
starting is assisted by a filament in the combustion chamber, which is energized
by an external battery.
harmonic distortion - Distortion consisting of addition to the signal of
components whose frequencies are multiples (harmonics) of the original signal frequency.
It is produced by an amplifier or other device which is nonlinear (does not give
the same ratio of output to input for all input amplitudes).
heterodyne - A different frequency (beat) produced by combining two frequencies.
hole - Absence of an electron normally present in an atom; a positive charge.
The action of some transistors often is explained by referring to movement of holes
or positive charges, rather than movement in the opposite direction of electrons
or negative charges.
microammeter - A meter for the measurement of current flow, which is calibrated
in microamperes, or millionths of an ampere.
milliampere - One-thousandth of an ampere.
modulated - Varied in amplitude, frequency, or some other quality. Radio-frequency
signals are modulated in order to carry signals of lower frequency, such as sound
or picture signals.
multitester - A meter which is a combination of a voltmeter, an ohmmeter,
and (often) an ammeter.
octal - Designation of one of the standard types of tube base or the socket
to fit it. The base has eight equally spaced pins and a centrally located boss,
which is made of insulating material and has a key to prevent improper insertion
of the tube in the socket. The loctal tube base is similar, except that its pins
are smaller in diameter and the central boss is of metal and has a groove which
fits a one-turn spring in the socket, to hold the tube.
oscillator - A vacuum-tube or transistor circuit or other device which
produces an alternating-current power output without mechanical rotation.
plate dissipation - The part of the power applied to the plate circuit
of a vacuum tube which does not appear as signal output, but is dissipated as heat
in the plate of the tube.
push-pull - An arrangement of two vacuum tubes in an amplifier so that
the input signal is applied in opposite phases to the two tubes and the signal outputs
are combined in phase. This arrangement reduces even-harmonic distortion.
regeneration - Positive feedback in detectors and amplifiers. Increases
gain and distortion and may produce oscillation.
saturate - To reach the maximum possible value of some quantity, such as
magnetization in the core of an inductor or electron flow in a vacuum tube from
cathode to plate.
servo-motor - A special electric, hydraulic, or other type of motor used
in control apparatus to convert a small movement into one of greater amplitude or
greater force.
signal generator - A test instrument providing electrical power substantially
similar in amplitude, frequency, and other qualities, to signals found in electronic
equipment.
signal tracer - A test instrument for detecting the presence of a signal
in electronic equipment and, with some signal tracers, measuring its amplitude,
frequency, or other qualities.
superheterodyne - A receiver in which all incoming radio-frequency signals
are mixed with the output of an oscillator to produce a heterodyne or beat frequency.
The oscillator frequency is variable so that the beat produced with any desired
signal can be adjusted to a certain frequency. The beat-frequency signal is fed
to a fixed-frequency (intermediate-frequency) amplifier, where greater and more
uniform gain and selectivity can be obtained than at the original radio frequency.
superregenerative - A type of regenerative detector in which the tendency
to oscillation is controlled by a quenching voltage of ultrasonic frequency which
periodically allows the gain to increase, then reduces it. The quenching voltage
can be produced by the detector tube itself or by a separate oscillator. This type
of detector has great sensitivity, but poor selectivity.
tone control - 1. In a radio receiver or an audio amplifier, means provided
to change the relative response to audio signals of different frequencies; effects
which can be produced are treble boost or attenuation and bass boost or attenuation.
2. In radio control of models, a system wherein the radio signal is modulated by
audio tones and control is achieved by keying the modulating tones on and off, instead
of keying the r.f. carrier.
v.t.v.m. - Vacuum-tube voltmeter, a voltmeter using one or more vacuum
tubes to increase the sensitivity of the basic meter movement, so that measurements
can be made in a circuit without drawing much current and without disturbing very
much the normal operating conditions of the circuit. May also be a combination voltmeter,
ohmmeter, and ammeter.
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Abbreviations
a.c. - alternating current
a.f. - audio frequency
a.f.c. - automatic frequency control
a.g.c. - automatic gain control
AM - amplitude modulation
amp. - ampere
ARRL - American Radio Relay League
a.v.c. - automatic volume control
BCI - interference with broadcast reception
b.f.o. - beat frequency oscillator
cps - cycles per second
c.t. - center-tapped
c.w. - continuous wave
db - decibel
dbm - decibels above one milliwatt
d.c. - direct current
d.c.c. - double cotton covered (wire)
d.p.d.t. - double-pole, double-throw
d.p.d.t. - double-pole, single-throw
DX - distance
elec. - electrolytic
FCC - Federal Communications Commission
FM - frequency modulation
freq. - frequency
GMT - Greenwich Mean Time
hi fi - high fidelity (of sound reproduction)
hy. - henry
i.f. - intermediate frequency
K - kilo (one thousand)
kc. - kilocycle
M - mega (one million)
ma. - milliampere
mc. - megacycle
meg. - megohm
mike - microphone, microfarad
mil - milliampere
m.o.p.a. - master oscillator, power amplifier
mu - amplification factor
μfd. - microfarad
μμfd. - micromicrofarad
mw. - milliwatt
m.w. - medium wave
PA - power amplifier
p.a. - public address
PM - phase modulation, permanent magnet (speaker)
pos. - position (of a switch)
pot. - potentiometer
pri. - primary
R-C - resistance -coupled
R/C - radio control
rect. - rectifier
res. - resistor
RETMA - Radio-Electronics-Television Manufacturers Association
r.f. - radio frequency
r.m.s. - root mean square
sec. - secondary
SN - self-neutralizing (escapement)
s.p.d.t. - single -pole, double-throw
spkr. - loudspeaker
s.p.s.t. - single-pole, single-throw
s.w. - short-wave
SWL - short-wave listener
sync. - synchronization
t. - turns (of a coil)
trans. - transformer
TV - television
TVI - interference with television reception
u.h.f. - ultra high frequency
v. - volt
v.f.o. - variable frequency oscillator
v.h.f. - very high frequency
VR - voltage regulator
v.t.v.m. - vacuum -tube voltmeter
vu - volume unit
w. - watt
wpm - words per minute
tr. - transmitter
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