(
Citizen's
Band radio) The frequency band of 40 channels for public radio transmission in the 27 MHz band. Introduced in 1945, primarily for farmers and the Coast Guard, CB radio initially operated in the 460-470 MHz frequency range.
CB radio uses the same frequencies for sending and receiving on each channel, which is why two people cannot talk to each other at the same time (see
half-duplex). With a range of approximately five miles, CB radios were popular with truck drivers in the 1970s and 1980s until mostly giving way to cellphones. See
ISM band and
personal radio services.