O
OMNIDIRECTlONAL ANTENNA— An antenna that
radiates or receives equally well in all directions, except
directly off the ends.
OSCILLATOR— An electrical circuit that generates
alternating current at a particular frequency.
P
PARABOLIC ANTENNA— An antenna that radiates its
signal back into a large reflecting surface (called the
dish) for radiation.
PERIOD (of a wave)— The time required to complete one
cycle of a waveform.
POLARIZATION (of antennas)— The plane (horizontal
or vertical) of the electric field as radiated from a
transmitting antenna.
R
RADHAZ (RADIATION HAZARD)— Electromagnetic
radiation hazard generated from electronic equipment.
RADIATION FIELD— The electromagnetic field that
radiates from an antenna and travels through space.
RADIATION RESISTANCE— The resistance that, if
inserted in place of an antenna, would consume the same
amount of power that is radiated by the antenna.
RECIPROCITY— See antenna reciprocity.
RED— Plain text or unencrypted information
REFLECTED WAVE— An electromagnetic wave that
travels back toward the transmitter from the antenna
because of a mismatch in impedance between the two.
REFLECTION— Occurs when a radio wave strikes the
Earth’s surface at some distance from the transmitting
antenna and is returned upward toward the atmosphere.
RF (RADIO FREQUENCY)— A frequency in the range
within which radio waves can be transmitted.
Frequencies used for radio communication fall between
3kHz and 300GHz.
RF ENERGY— Radio frequency energy. Energy
produced at the output of a transmitter.
S
SATELLITE COMMUNICATION (SATCOM)— A
type of worldwide, reliable, high-capacity, secure, and
cost-effective telecommunications system utilizing
satellites.
SHF (SUPER HIGH FREQUENCY)— The band of
frequencies from 3 GHz to 30 GHz.
SIGNAL— Detectable transmitted energy that can be used
to carry information.
STANDING WAVES— The stationary waves that buildup
along an antenna during radiation.
SWITCHBOARD— Device that connects receiver outputs
to numerous pieces of equipment.
SWR (STANDING-WAVE RATIO)— A term used to
express the degree of resonance attained between the
antenna and the transmission line when being tuned for
transmission.
T
TRANSMISSION LINE— A device designed to guide
electrical or electromagnetic energy from one point to
another.
U
UHF (ULTRA HIGH FREQUENCY)— The band of
frequencies from 300 MHz to 3 GHz.
UNIDIRECTIONAL ANTENNA— An antenna that
radiates in only one direction.
V
VHF (VERY HIGH FREQUENCY)— The band of
frequencies from 30 MHz to 300 MHz.
VLF (VERY LOW FREQUENCY)— The band of
frequencies from 3 kHz to 30 kHz.
W
WAVEFORM— The shape of an electromagnetic wave.
WAVELENGTH— The distance traveled, in feet or
meters, by a radio wave in the time required for one
cycle.
AI-3
