18WuD2x

300 frequency bias • frequency drift
frequency bias An intentional change in the frequency
of a transmitted signal.
frequency bridge 1. Any alternating-current
bridge, such as the Wien bridge or resonance
bridge, that can be nulled at only one frequency
for a given set of bridge-arm values. 2. Any alternating-current
bridge that is used to measure
unknown frequencies.
frequency calibrator A device, such as a crystal oscillator,
that provides a signal of precise frequency
with which other signals can be compared. Also
see SECONDARY FREQUENCY STANDARD.
frequency changer 1. A superheterodyne converter
(see CONVERTER). 2. A motor-generator in
which the output voltage has the same value as
the input voltage, but is of a different frequency.
3. See FREQUENCY-MULTIPLYING TRANS-
FORMER. 4. See FREQUENCY MULTIPLIER.
frequency-change signaling See FREQUENCY-
SHIFT KEYING.
frequency channel A relatively narrow segment of
a frequency band allocated to a station in a particular
service. The bandwidth of the channel depends
on the type of modulation used, the type of
data to be transmitted, and the speed or fidelity of
the data to be transmitted.
frequency comparator A device, such as an oscilloscope
or zero-beat indicator, used to check one
frequency against another. Also see FREQUENCY
COMPARISON.
frequency comparison The observation of a current
or voltage of one frequency for similarities in
that of another frequency. Comparisons (as in
frequency matching) can be made by audio
means, by visual means, or both. Common instruments
used are oscilloscopes, beat-note detectors,
and beat-note meters.
frequency-compensated attenuator An attenuator,
such as one in an electronic voltmeter or
wideband oscilloscope, that has been modified by
the addition of capacitors or inductors to achieve
reasonably flat response over a wide range of frequencies.
frequency compensation The modification of a
circuit, such as an amplifier or attenuator, by the
addition of capacitors or inductors to tailor its response
at specified frequencies.
frequency control 1. An adjustable component
(potentiometer, variable capacitor, or variable inductor)
with which the frequency or frequency response
of a circuit is adjusted. 2. A device, such
as a quartz crystal or tuning fork, that automatically
sets the frequency of an oscillator.
frequency conversion The process of changing a
signal from one frequency to another, usually
without altering the signal bandwidth. In some
cases, a signal is turned “upside down” by this
process [e.g., an upper-sideband (USB) signal
might be changed to a lower-sideband (LSB) signal].
Generally accomplished by means of a
MIXER.
frequency converter 1. An active or passive device
for changing the frequency of a signal. 2. The
mixer in a superheterodyne circuit.
frequency correction Manual or automatic resetting
of a deviated frequency to its original value.
frequency counter An instrument that counts signal
cycles or pulses over a standard time base (a
frequency measurement). Often used to accurately
measure the frequencies of radio or television
signals; in this application, it is a precision
FREQUENCY METER.
frequency cutoff See CUTOFF FREQUENCY.
frequency detector See FREMODYNE DETEC-
TOR.
frequency deviation 1. The degree to which a frequency
changes from a prescribed value. Thus, if
the frequency of a 1000-Hz oscillator drifts between
990 and 1010 Hz, the deviation is ±10 Hz.
2. In a frequency-modulated (FM) signal, the
amount of instantaneous frequency shift above
and below the unmodulated carrier frequency.
frequency-deviation meter In frequency-modulation
(FM) communications operations, a meter
that gives a direct reading of frequency deviation
resulting from a modulating signal. It uses either
a tuned circuit or a frequency comparator.
frequency difference 1. In a superheterodyne circuit,
the difference between the signal frequency
and the oscillator frequency. 2. In any beatfrequency
operation, the quantity f 2 – f 1 , where f 2
is the higher frequency and f 1 is the lower
frequency. Compare FREQUENCY SUM.
frequency discriminator See DISCRIMINATOR.
frequency distortion A form of distortion in which
the amplification of some frequencies is different
from that of others.
frequency distribution See DISTRIBUTION, 2.
frequency diversity The transmission and reception
of signals at two or more frequencies for the
purpose of reducing the effects of fading. It is generally
used in long-distance, high-frequency circuits.
frequency divider A circuit or device whose output
frequency is a fraction of the input frequency.
Compare FREQUENCY MULTIPLIER.
frequency-dividing network See CROSSOVER
NETWORK.
frequency-division multiplex A form of multiplesignal
parallel transmission in which a single carrier
is modulated by two or more signals
simultaneously.
frequency doubler A circuit that multiplies an input
frequency by two. If a doubler’s input circuit
is tuned to frequency f, then its output circuit is
generally tuned to 2f. Frequency doubling is performed
by various nonlinear devices, including
transistors, varactors, and biased diodes.
frequency drift An undesired, usually gradual,
change in the frequency of a signal from its intended
frequency or channel; expressed in hertz
or kilohertz.