A closed-circuit radio is a
radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...
that emits over a very small range, typically a college campus. This system can be achieved from two ways:
*By tying into the
PA System
A public address system (or PA system) is an electronic system comprising microphones, amplifiers, loudspeakers, and related equipment. It increases the apparent volume (loudness) of a human voice, musical instrument, or other acoustic sound sou ...
*By using existing
power lines
Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines that facilitate this movement form a ''transmission network''. This is d ...
, telephones lines, pipes, etc. to transmit a
carrier currentClosed-circuit Radio Network in Homes Seen
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References
Radio communications
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