All CB radios operate on AM, which is the same type of transmission as a typical AM radio station.  In addition, some higher-end CB radios are equipped with single sideband (SSB), which is a different mode of transmission.  People using a regular CB radio cannot properly receive SSB signals, it will sound garbled. 

Please note that single sideband does not use different frequencies.  For example channel 19 has a frequency of 27.185MHz.  When you switch to single sideband, channel 19 is still 27.185MHz.  The mode of transmission changes, but the frequency does not change.

A single sideband CB can operate on more channels than a regular CB.  There are 40 upper-sideband channels, 40 lower-sideband channels, and the regular 40 CB channels.  In addition, higher power is allowed when using single sideband.  12 watts PEP is allowed, versus 4 watts on regular CB.  A single sideband radio therefore has better range than a regular CB (when operating on the sidebands).

The advantages of single sideband:

  • More channels
  • Higher power (12 watts is allowed on SSB, only 4 watts is allowed on AM)
  • Quieter reception

Only a small fraction of CB owners have a single sideband radio.  Single sideband operation is more common among dedicated CB enthusiasts.