Page 301 - Electrical Engineering Dictionary

used as the free input model. Usually free in- Fremdhold integral equation a linear in-
put model is driven by a white noise stochas- tegral equation wherein the limits of integra-
tic process or by a sequence of set bounded tion are fixed.
— but otherwise time-independent — quan-
tities. frequency the repetition rate of a periodic
signal used to represent or process a commu-
nication signal. Frequency is expressed in
free running frequency the frequency at
units of hertz (Hz). 1 Hz represents one cy-
which an oscillator operates in the absence
cle per second, 1 MHz represents one million
of any synchronizing input signal. The fre-
cycles per second, and 1 GHz represents one
quency is usually determined by a time con-
billion cycles per second.
stant from externally connected resistance
and capacitance.
frequency chirp a monotonic change in
optical frequency with time; often used for
free space loss the propagation loss expe- laser radar ranging in analogy with conven-
rienced between two isotropic antennas in a tional radar and for ultrashort pulse gener-
vacuum resulting from spreading of power ation via pulse compression or autocorrela-
over spherical wavefronts centered at the tion. See also chirp signal.
transmitting antenna and from the finite aper-
ture of the receiving antenna. The free space
frequency compensation the modifica-
loss increases proportional to the square of
tion of the amplitude–frequency response of
the distance from the antenna and the square
an amplifier to broaden the bandwidth or to
of the frequency.
make the response more nearly uniform over
the existing bandwidth.
free system See unforced system.
frequency converter an equipment or cir-
cuit that converts an RF signal to an interme-
free-page list a linked-list of information
diate (IF) signal in receivers. It converts an
records pointing to “holes” (i.e., free page
IF signal to an RF signal in transmitters.
frames) in main memory.
frequency correlation function a func-
free-space interconnect interconnect us- tion characterizing the similarity of a re-
ing optical elements such as lenses, gratings, ceived signal with respect to a shift in fre-
and holograms, in which optical signals may quency.
cross each other in the space. The main
advantages are high interconnection density frequency deviation in a frequency mod-
and parallelism, and dynamic reconfigura- ulated system, the number of hertz the carrier
tion. is varied during the modulation process.

free-wheeling diode a diode connected in frequency domain representation of a
parallel with the load of a half-wave rectifier signal by frequency components, such as its
to prevent the return of energy from the load Fourier transform.
to the source. Due to the stored energy in
the inductive load, the current must continue frequency domain sampling a proce-
after the source voltage becomes negative. dure that is a dual of the time-domain sam-
The free-wheeling diode provides a path for pling theorem, whereby a time-limited signal
the current to circulate and allows the diode can be reconstructed from frequency-domain
or SCR in the rectifier to turn off. samples.

c
2000 by CRC Press LLC