Citizens' band radio (CB) is, in the United States, a system of short distance radio communication between individuals on a selection of 40 channels within the single 27 MHz (11 meter) band.

Formed following a decision in 1945 by the US government that its citizens should have this right, the CB radio service should not be confused with FRS, GMRS or Amateur Radio. CB does not require a license and unlike Amateur Radio CB may be used for commercial communication. The 11-meter band was taken from the Amateur Radio service for the Citizen's Band. But it was not until the 1970s, when technology had advanced to reduce costs, that the CB market prospered, US truckers being at the head of the boom. Many CB clubs were formed and a special CB language evolved.

Originally CB did require a license and the use of a call sign but during the CB craze of the 1970's many people ignored this requirement and used made up nicknames called "handles". The use of handles instead of call signs is related to the common practice of using the radios to warn other drivers of speed traps during the time when the United States dropped the national speed limit to 55 mph (89 km/h). Eventually the license requirement was dropped. The early CB radios sold for mobile use in the US had only 23 channels and almost all were AM only, although Single Side Band was also allowed. In 1977, an additional 17 channels were added for a total of 40 channels, to relieve some of the overcrowding on the original 23 channels.

Maximum power level was five watts for AM and 12 watts (peak power) for single side band, although more powerful external "linear" amplifiers were commonly and illegally used.

Channels near 462 MHZ in the UHF band were formerly allocated to the Citizen's Band "Class A" radio service but this band was never commonly used. In 1973 an attempt was made to allocate frequencies near 220 MHZ to "Class E" Citizen's Band service but this was strongly opposed by amateur radio organizations and was never implemented. The intent was to eliminate some of the interference and skip that existed on the shortwave frequencies. While the extended propagation characteristics on this band was of considerable interest to radio hobbyists, interference from distant stations limited the usefulness of CB for its original purpose.

The FCC recommended the use of ten-codes and these were used, often in a shortened form, but also many slang terms were developed.

CB is still a popular hobby in many countries though its meaning as a method of communication among the general public has diminished recently, due to new developments such as the internet and mobile phones. CB radio is still a popular method of communication among semi truck drivers. Commercial drivers use CB to communicate to other truck drivers directions, traffic problems, and other things of importance.

Legitimate, short_range use of CB radio is sometimes made difficult by uncooperative users or illegal high_power transmitters, which are capable of being heard hundreds of miles (km) away. In the United States, the vast number of users and the low financing of the regulatory body mean that the regulations are only actively enforced against the most severe interfering stations, which makes legitimate operations on the Citizen's Band unreliable. Other services such as VHF MURS and in the UHF band FRS and GMRS exist now to provide the reliable short-range communication service originally envisioned for the Citizen's Band.

The low cost and simple operation of CB equipment gave access to a communications medium that was previously only available to specialists. The "boom" in CB usage in the 1970's is somewhat similar to the advent of the Internet in the 1990's. The many restrictions on the authorized use of CB lead to widespread disregard of the regulations, most notably in antenna height, distance restriction for communications, licencing and the use of call signs, and allowable transmitter power.

Many radio hobbyists operate illegitimately in the so_called "free band", using either Citizen's Band equipment that has been modified for extended frequency range and higher power, or else amateur radio equipment operated outside the assigned amateur 10 meter band. Such operations are not part of the legally authorized Citizen's Band service and should not be called "CB". Out_of_band operations may interfere with licenced, public safety, commercial, or military users of these frequencies. Illegal transmitters may not meet good engineering practice for harmonic distortion or "splatter", and resulting interference to licenced radio spectrum users will often attact the attention of regulating authorities.

Channel Assignments

To simplify selection of an operating frequency, CB equipment divides the authorized band into channels numbered 1 to 40. Frequencies for the channels are 10 kHz apart, but channel numbers are not strictly sequential with frequency. See 27 MHz FCC Bandplan. Radio remote control for models and toys operate on frequencies near CB authorized channels.

Popular CB channels (United States)