CB radio is most frequently used for conversations between places that are not linked by telephone. Many motorists and truck drivers use it to talk with other highway travelers or people who are in an office or at home. 

Most CB sets are devices called transceivers, which consist of a transmitter and a receiver. Some CB devices receive radio signals but do not transmit them.

 Most CB transmitters broadcast for distances of fewer than 5 miles (8 kilometers) in cities and up to 20 miles (32 kilometers) in rural areas. The broadcast range varies with the atmospheric conditions, the terrain, the design and height of the set's antenna, and the amount of power supplied to the transmitter. Government regulations in the United States and Canada limit the power of a CB transmitter to a maximum of 4 watts. In both countries, CB radio has 40 channels, with frequencies of 26.965 to 27.405 megahertz. The Canadian CB is called General Radio Service. 

In the United States, there are no licensing requirements for the operation of citizens band radios. But Canada requires a CB transmitter of more than one-tenth watt to be licensed. A Canadian citizen may obtain a General Radio Service license from the nearest district office of the Department of Communications. 

Remote controls for such devices as model airplanes and automatic garage-door openers also operate on CB radio frequencies.

Source: World Book Encyclopedia

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