Single-sideband transmission (SSB) is a method of transmitting audio based on amplitude modulation in which only one sideband is transmitted. Essentially, the carrier and one sideband of an AM signal are removed, leaving only the other sideband. Assuming both sidebands are symmetric, no information is lost in the process. The required signal bandwidth is reduced and, since the final RF amplification is concentrated in a single sideband, effective power output is greater than normal AM. The carrier and redundant sideband account for well over half of the power output of an AM transmitter.
To decode the signal at the receiving end the original AM mode is synthesized by adding a carrier signal to the lone sideband. The signal can then be demodulated as a standard AM signal. Because the synthesized carrier is locally generated it of much higher quality than a transmitted one, which contributes to a higher quality received signal. An SSB signal cannot be demodulated by standard AM receivers because of the lack of a reference carrier signal.
SSB was pioneered by long distance telephone companies in the 1930s for use over wire lines. Radio amateurs began to experiment with the method seriously after World War II. It has become a de facto standard for long distance voice radio transmissions since then.
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