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.
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
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
Earths 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.
SATELLITE COMMUNICATION (SATCOM) A
type of worldwide, reliable, high-capacity, secure, and
cost-effective telecommunications system utilizing
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 LINE A device designed to guide
electrical or electromagnetic energy from one point to
UHF (ULTRA HIGH FREQUENCY) The band of
frequencies from 300 MHz to 3 GHz.
UNIDIRECTIONAL ANTENNA An antenna that
radiates in only one direction.
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.
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