27.215 MHz
Channel 21 sits at 27.215 MHz and is used mainly for general chat. Like most of the 40-channel band, exact usage varies by region and time of day — the best way to know what a channel is used for near you is to listen before you transmit.
Like all AM CB channels, the legal power limit here is 4 watts, and no license is required to transmit.
All 40 CB channels are fixed nationwide by the FCC between 26.965 and 27.405 MHz. Channel uses like the ones described here are widely-observed operator conventions, not law — the frequency is fixed, but who's talking on it depends on your region and the time of day.
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