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Cobra 18 WX ST II mobile CB radio with microphone
Citizens' Band radio (also known as CB radio) is a system of short-distance radio communications between individuals on a selection of 40 channels within the 27-MHz (11 m) band. Citizens' Band is distinct from the Family Radio Service, GMRS, Multi-Use Radio Service and amateur radio (Ham). In many countries CB operation does not require a license, and (unlike amateur radio) it may be used for business or personal communications. Like many other two-way radio services, any Citizens' Band channel is shared by many users. Only one station may transmit in a channel at a time; other stations must listen and wait for the shared channel to be available. Also, the system works in half-duplex mode, which means we may transmit and receive information, but not both at the same time.
Typical center-loaded mobile CB antenna. Note the loading coil, which shortens the antenna's overall length.
The channel assignments in India are different from the band plans used elsewhere. The Indian band plan consists of 40 frequencies spaced a relatively tight eight kHz apart, plus a few offset channels used for mountaineering and radio-controlled devices. Many of the channels are reserved for specific purposes such as forestry, disaster relief, and sporting events. The frequency band allocated for this purpose in India is 26.957-27.283 MHz. Nonetheless, the effective radiating power used for Citizens Band is limited within 5 Watt in India.