So how does this all work? When you mix together two signals with different frequencies, you produce two new signals -- one with a frequency that's the sum of the first two frequencies, the other with a frequency that's the difference between the first two frequencies. Mix an audio tone that has a frequency of 1 kHz (one kilohertz, or one thousand cycles per second) with radio carrier signal of 1000 kHz, and you get two new signals, at 999 kHz and at 1001 kHz. The 999 kHz signal is the lower sideband (LSB), and the 1001 kHz signal is the upper sideband (USB). The carrier signal -- a steady, continous signal of unvarying frequency -- sits between the two sidebands, not really carrying anything. All it really does is serve as a zero-reference for the sidebands -- a radio receiver mixes the carrier with the sidebands, and out pops the original audio signal. But that reference signal can be created by a circuit in the receiver, so you don't even have to transmit the carrier. An SSB radio transmitter suppresses the carrier, and one of the redundant sidebands, and transmits the operator's voice in less than half the bandwidth of an AM signal, and with much more efficient use of energy.