Thursday, January 12, 2012

Citizens Band Radio


Citizens Band Radio

Citizens Band Radio, radio channels used for two-way, short-distance business and personal communications. Citizens band radio, or CB as it is commonly known, was initiated in the United States in 1947 when the Federal Communications Commission (FCC) opened the UHF (ultrahigh frequency) 460-470 MHz band to licensees from the general public. In 1958 the FCC reallocated part of the 11-m band (27 MHz) previously shared by amateur radio and industrial users to the Citizens Radio Service. The band was divided into 29 channels, 6 of which were reserved for radio-control devices such as garage-door openers. By the early 1980s more than 20 million CB sets were operating on 40 channels in the U.S. The CB fad was waning by that time, however, and in 1983 the FCC ceased requiring licenses for CB operation.
Recent CB transceivers use a digital synthesis circuit with two crystals to generate the 80 basic frequencies of the 40-channel system by means of integrated-circuit silicon-chip technology.
Citizens band transmitters, which are restricted to a maximum power input of 5 watts and output of 4 watts, have ranges of up to about 24 km (about 15 mi). Citizens band radio continues to be used by the drivers of trucks and automobiles, by factory personnel for internal mobile communications, and by other workers and private citizens. Channel 9, the emergency channel, is monitored by highway patrol and police departments and by citizen volunteer groups.

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