Page 302 - Electrical Engineering Dictionary

frequency distortion caused by the pres- as slow frequency hopping, otherwise as fast.
ence of energy storage elements in an am- Frequency hopping is used for counteracting
plifier circuit. Different frequency compo- intentional interference, frequency selective
nents have different amplifications, resulting fading, and as a multiple access technique
in frequency distortion, and the distortion is (FH-CDMA).
specified by a frequency response curve.
frequency independent antenna antenna
frequency division duplex (FDD) a tech- with very large bandwidths. Upper fre-
nique based on the allocation of two separate quency can be about 40 times higher than
frequency bands for the transmission in both the lower frequency. Examples: spiral and
directions in a link. FDD typically requires a log periodic antennas.
guard band between the two frequency bands
in order to eliminate interference between the frequency modulation (FM) angle mod-
transmitter and receiver at a terminal. In a ulation in which the instantaneous frequency
full duplex communication system, informa- of a sine-wavecarrier is caused todepart from
tion flows simultaneously in both directions the carrier frequency by an amount propor-
between two points. tional to the instantaneous value of the mod-
ulating wave.
frequency division multiple access
(FDMA) a multiple-access technique frequency nonselective channel a radio
based on assigning each user a unique fre- channel that has a uniform transfer function
quency band upon which transmission takes over the bandwidth of information signal. In
place. See also time division multiple access, such a channel, fading leads to reduced SNR
code division multiple access. at the receiver, but does not lead to distortion
of the symbol shape and hence intersymbol
frequency division multiplexing (FDM) interference.
refers to the multiplexing of signals by shift-
ing each signal to a different frequency band. frequency pulling shift of the frequency
See also frequency division multiple access. of a laser oscillation mode from the empty
cavity or nondispersed cavity frequency to-
frequency domain storage an optical ward the center frequency of the amplifying
data storage technique in which individ- transition.
ual bits are stored by saturating or bleach-
ing spectral holes into an inhomogeneously frequency regulation the change in the
broadened absorption spectrum. Usually, frequency of an unloaded generator with re-
this hole burning is accomplished using elec- spect to its frequency in a fully-loaded state.
tromagnetic fields of discrete frequencies. Typically applied to small, isolated power
The maximum frequency domain storage systems such as emergency power units.
density is given by the ratio of inhomoge-
neous width to homogeneous width of the frequency relay a protective relay which
absorption spectrum. monitors the frequency of the electric power
system.
frequency hopping a system where the
carrier frequency used for modulation is frequency resolution a measure of the
changed according to some predetermined ability of a system to resolve different fre-
hopping pattern. The receiver hops accord- quencies in a signal. As the frequency resolu-
ing to the same pattern in order to retrieve the tion increases, more finely-spaced frequency
information. If the rate of change is lower or components can be resolved. The time res-
equal to the data rate, the process is known olution of a system is roughly inversely pro-

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