CB Radio Modes

Modulation is the procedure whereby speech, music, and other "intelligence" is put into the radio waves created by a transmitter. The various ways of modulating a radio signal are called modes.

An un-modulated radio signal is called a carrier. When you listen to "dead air" in between songs or announcements on a radio station, you are actually "hearing" the carrier.

Whilst a carrier has no intelligence, you can tell it is being broadcast given the way it quiets the background noise on your radio.

The different modes of modulation have their advantages and disadvantages. Here is a summary:

Continuous Wave (CW)

CW is the most basic type of modulation. The output of the transmitter is switched on and off, commonly to create the characters of the Morse code.

CW transmitters are basic and affordable, and the transmitted CW signal does not take up very much frequency space (typically under 500 Hz). The CW signals will be difficult to hear on a normal receiver; you'll just hear the faint quieting of the background noise as the CW signals are transmitted.

 To get over this issue, shortwave and ham radio receivers contain a beat frequency oscillator (BFO) circuit. The BFO circuit generates an internally-generated second carrier that "beats" against the received CW signal, generating a tone that turns on and off in step with the received CW signal.

This is exactly how Morse code signals are received on shortwave.



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