Citizens' band radio

Citizens band radio (also known as CB radio) is, in many countries, a system of short-distance radio communications between individuals typically on a selection of 40 channels within the 27 MHz (11 m) band. Citizens band is distinct from other personal radio service allocations such as FRS, GMRS, MURS, UHF CB and the Amateur Radio Service ("ham" radio). 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, citizens band channels are shared by many users. Only one station may transmit at a time; other stations must listen and wait for the shared channel to be available. It is customary for stations waiting to use a shared channel to broadcast the single word "Break" during a lull in the conversation. This informs people using the channel that others are waiting.

A number of countries have created similar radio services, with varying technical standards and requirements for licensing. While they may be known by other names, such as the General Radio Service in Canada, they often use similar frequencies (26 to 28 MHz), have similar uses, and similar technical standards. Although licenses may be required, eligibility is generally simple. Some countries also have personal radio services in the UHF band, such as the European PMR446 and the Australian UHF CB.

The citizens band radio service originated in the United States as one of several personal radio services regulated by the Federal Communications Commission (FCC). These services began in 1945 to permit citizens a radio band for personal communication (e.g., radio-controlled model airplanes and family and business communications). In 1948, the original CB radios were designed for operation on the 460–470 MHz UHF band. There were two classes of CB radio: "A" and "B". Class B radios had simpler technical requirements, and were limited to a smaller frequency range. Al Gross established the Citizens Radio Corporation during the late 1940s to manufacture Class B handhelds for the general public.

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