AI-3
GROUP—A collection of units, assemblies, subassemblies, and parts. It is a subdivision of a set or
system but is not capable of performing a complete operational function.
HAND OVER—The operation where one earth terminal yields control to another as a satellite moves out
of its area of coverage.
HARMONIC—An exact multiple of the fundamental frequency. Even harmonics are 2, 4, and so on,
times the fundamental. Odd are 3, 5, and so on, times the fundamental frequency.
HELIX—A large coil of wire. It acts as a coil and is used with variable inductors for impedance
matching of high-power transmitters.
HELIX HOUSE—A building at a transmitter site that contains antenna loading, coupling, and tuning
circuits.
HETERODYNING—The mixing of the incoming signal with the local oscillator frequency. This
produces the two fundamentals and the sum and difference frequencies.
HIGH FREQUENCY—The band of frequencies from 3 megahertz to 30 megahertz.
IMAGE FREQUENCY—An undesired frequency capable of producing the desired frequency through
heterodyning.
INCLINED ORBIT—Orbits where there is some amount of inclination. These include equatorial and
polar orbits.
INCOHERENT—This refers to radiation on a broad band of frequencies.
INTELLIGENCE—Any signal that conveys information (voice, teletypewriter, facsimile).
KEYER—A device that changes dc pulses to mark and space modulation for teletypewriter
transmissions.
LASER—An acronym for light amplification by stimulated emission of radiation.
LISSAJOUS PATTERN—A combined, simultaneous display of the amplitude and phase relationships
of two input signals on a CRT.
LOW FREQUENCY—The band of frequencies from 30 kilohertz to 300 kilohertz.
MARKING—The state where a circuit is closed and current flows in teletypewriter operation.
MEDIUM ALTITUDE ORBIT—An orbit from 2,000 to 12,000 miles above the earth. The rotation rate
of the earth and satellite are quite different, and the satellite moves quickly across the sky.
MEDIUM FREQUENCY—The band of frequencies from 300 kilohertz to 3 megahertz.
MTDS—An abbreviation for the marine tactical data system.
MULTICOUPLERS—Couplers patch receivers or transmitters to antennas. They also filter out
harmonics and spurious responses, and impedance-match the equipment.
MULTIPLEXING—A method for simultaneous transmission of two or more signals over a common
carrier wave.
