CB radio allows for the use of several different types of modulation methods or "modes." Single Side Band or SSB modulation is a type of amplitude modulation that uses less than half the bandwidth of a traditional AM signal. SBB is divided into Upper Side Band and Lower Side Band. SSB allows for communication over longer distances, including international locations.
While SSB uses less bandwidth, FM mode occupies the widest frequency band and offers much richer sound quality. SBB has a longer effective range than FM, but as an AM mode, it is still subject to background noise and interference.
Keep in mind that SSB radios require additional hardware and are a more expensive option for CB radio, typically costing $30 – $50 and up more than AM-only radio units.
SSB is also more complex to operate and is typically only recommended for advanced users; it includes a "clarifier" control that requires the user to manually tune in to an incoming signal each time.