18WuD2x

Fraunhofer region • frequency band 299
pears to come from a single point located near the
actual antenna.
free air resonance For a speaker, the resonant frequency
or frequencies exhibited when the device
is not mounted in a cabinet.
free carrier A free electron or, in a semiconductor
material, the equivalent hole. Also see ELEC-
TRON and HOLE.
free charge The portion of a charge on a conductor
that, being unaffected by a neighboring charge,
will escape to ground when the conductor is
grounded. Compare BOUND CHARGE.
free electron 1. An electron situated in one of the
outer orbits of an atom, held loosely by the nucleus.
Because free electrons can easily escape
the attraction of atomic nuclei, they will drift
among atoms if the material is subjected to an
electric potential. The result is electric current.
Also see ELECTRON and BOUND ELECTRON. 2.
An electron that is not associated with any atomic
nucleus.
free field Data organized in a storage medium in
such a way that a data item or field can be anywhere
in the medium. Compare FIXED FIELD.
free impedance For a transducer, the input
impedance produced by a perfectly shortcircuited
load.
free magnetic pole A magnetic pole that is so well
isolated from its opposing pole that it experiences
little or no influence from the latter.
free magnetism A theoretical medium or fluid to
which magnetic effects are conventionally given.
The sum of free magnetism in any given object is
always zero. Within any small part of the field, the
free magnetism is thought of as flux lines. This
theoretical medium can be any nonmagnetic material.
free net In radio communications, a network in
which stations are free to communicate with
other stations in the net without constant supervision
by the net control station. Such communication
is carried out on a frequency
slightly above or below that of the net’s formal
operation.
free oscillations Oscillations in a circuit, such as
an inductance-capacitance (LC) tank, that continue
after excitation has been removed. Also see
FLYWHEEL EFFECT. Compare FORCED OSCIL-
LATIONS.
free path In a gas tube, the path taken by an electron
as it collides with atoms. Also see MEAN
FREE PATH.
free-power supply 1. A simple tuned radio-frequency
(RF) detector diode, used to rectify a radio
signal and supply small amounts of direct current
for the operation of low-powered transistor
circuits. 2. See SOLAR BATTERY.
free reel The supply reel of a magnetic-tape
recorder.
free-running frequency The frequency at which a
synchronized generator, such as a multivibrator
or self-excited oscillator, will operate when the
synchronizing voltage is removed.
free-running multivibrator See ASTABLE MULTI-
VIBRATOR and UNCONTROLLED MULTIVIBRA-
TOR.
free space Empty space; a theoretical ideal.
free-space loss Radio transmission loss disregarding
variable factors (a theoretical condition).
free-space pattern The ideal directivity pattern of
an antenna that is situated many wavelengths
above ground. In use, this pattern is modified by
reflections from ground.
free speed The angular velocity of an unloaded
motor.
free-standing display In a computer system, a remote
display unit for prompting peripheral operators.
freezing point Abbreviation, fp. The temperature
at which a liquid starts becoming a solid at normal
pressure. Compare MELTING POINT.
F region Also called F layer. A region of the ionosphere
with an altitude at night of approximately
175 miles. In daytime, the region splits into the
lower F1 region and the higher F2 region. This
layer is primarily responsible for long-distance
propagation of radio waves at high frequencies
(3 MHz to 30 MHz). At times it returns waves at
frequencies as high as about 70 MHz.
Fremodyne detector A frequency-modulation
(FM) detector that is essentially a conventional
amplitude-modulation (AM) circuit detuned to
one side of resonance (slope-tuned) to demodulate
a frequency-modulated signal. Also see
SLOPE DETECTOR.
French phone See CRADLEPHONE.
freqmeter Contraction of FREQUENCY METER.
frequency Symbol, f. The rate at which a phenomenon
is repeated. The basic unit of frequency
is the Hertz (Hz), which represents one
complete cycle per second. Common units encountered
in electronics are the kilohertz (kHz),
megahertz (MHz), and gigahertz (GHz), where
1 kHz = 10 3 Hz, 1 MHz = 10 6 Hz, and 1 GHz = 10 9
Hz. Occasionally, the terahertz (THz) is used;
1 THz = 10 12 Hz.
frequency-agile radar A radar system in which the
transmitter frequency is shifted in a predetermined
pattern for the purpose of avoiding detection.
A frequency-agile radar system, with a
complex frequency control program, is very difficult
to jam.
frequency allocation 1. The assignment of frequencies
to radio and allied services by the licensing
authority (in the United States, the
Federal Communications Commission). 2. A specific
assignment of a frequency or a band of frequencies.
Also see RADIO SPECTRUM.
frequency band A given range of frequencies, usually
specified for some application (e.g., the band
allocated for standard radio broadcast service).
Also see BAND.