18WuD2x

frequency function • frequency response 301
In
Tuned
to
2f
frequency doubler
Tuned
to
2f
Out
frequency function See PROBABILITY DENSITY
FUNCTION.
frequency indicator 1. A device that indicates
when a phase or frequency is common to two alternating
currents. 2. The display or dial that
shows the operating frequency of a radio receiver
or transmitter. 3. See FREQUENCY ME-
TER.
frequency keying See FREQUENCY-SHIFT KEY-
ING.
frequency meter An instrument for measuring the
frequency of an alternating current. The several
different types are used in different applications.
Also see AUDIO FREQUENCY METER, FRE-
QUENCY COUNTER, POWER-FREQUENCY ME-
TER, and WAVEMETER.
frequency-modulated radar See FM RADAR.
frequency modulation Abbreviation, FM. A
method of conveying intelligence in wireless communications
and broadcasting. The amplitude of
the carrier remains constant, and the instantaneous
frequency varies. One scheme for obtaining
this type of modulation is to apply the
modulating signal to a varactor in an oscillator.
Another method is to modulate the phase of the
oscillator signal. This causes small fluctuations
in the frequency as well, because any instantaneous
phase change shows up as an instantaneous
frequency change (and vice versa). Also
see AMPLITUDE MODULATION, PHASE MODU-
LATION, SINGLE SIDEBAND.
frequency modulation deviation 1. In frequency
modulation (FM), the largest difference between
the instantaneous signal frequency and the unmodulated
carrier frequency. 2. The maximum
bandwidth of an FM signal at its audio modulation
amplitude peak.
frequency modulator 1. A circuit or device that
modulates the frequency of an oscillator. 2. The
modulator section of an FM transmitter.
frequency monitor A device used (often continuously)
to check the frequency of a signal (e.g., a
frequency-deviation meter used in radio broad-
cast stations or a frequency meter used in electric-generating
stations).
frequency multiplier A circuit or device whose output
frequency is a multiple of the input frequency.
See, for example, FREQUENCY DOUBLER.
frequency-multiplying amplifier See MULTI-
PLIER AMPLIFIER.
frequency-multiplying transformer A magnetic
amplifier that generates harmonics of the supply
frequency. The effect results from the nonlinearity
of the transformer core material.
frequency offset 1. The difference between an actual
frequency and the desired frequency. 2. In a
communications transceiver, the difference between
the receiver frequency and the transmitter
frequency. In some modes, such as single-sideband
(SSB), the offset is normally zero. In other
modes, notably continuous-wave (CW) Morse
code, the offset is normally several hundred Hz.
3. See FREQUENCY SPLIT, 1.
frequency overlap 1. A common band of frequencies
between two adjacent channels in a communications
system. 2. A common frequency region
between two assigned bands. 3. A condition in
which parts of the sidebands of two signals occupy
the same range of frequencies.
frequency pulling A change in the frequency of a
circuit, especially of a self-excited oscillator, resulting
from the detuning effects of an external
circuit, device, or condition (such as body capacitance
or a change in the temperature).
frequency pushing An effect in which a current
change in a source oscillator causes a shift in
source frequency.
frequency quadrupler See QUADRUPLER, 2.
frequency quintupler See QUINTUPLER, 2.
frequency range 1. A communication system’s frequency
transmission limits, beyond which the
power output is attenuated below a specified
amount. 2. The frequency band or bands within
which a radio transmitter, receiver, or transceiver
is designed to operate.
frequency ratio counter See FREQUENCY RATIO
METER.
frequency ratio meter A meter that indicates the
ratio between two frequencies, and is useful in
the quick identification of harmonics.
frequency record A phonograph test disk containing
recordings of various frequencies at specified
amplitudes.
frequency rejection The elimination, usually by a
filter, of a single frequency (or narrow band of frequencies)
from a mixture of frequencies. Compare
FREQUENCY TRANSMISSION.
frequency relay A frequency-sensitive relay (see
SELECTIVE RELAY, 1).
frequency response A performance characteristic
that describes the operation of a device or circuit
over a specified range of signal frequencies (e.g.,
the gain-versus-frequency characteristic of an
amplifier).