SingleSideband

Singlesideband, commonly called single-sideband (SSB), is a form of amplitude modulation in which the carrier is suppressed and only one of the two symmetric sidebands is transmitted. The transmitter outputs either the upper sideband (USB) or the lower sideband (LSB). Eliminating the carrier and one sideband reduces the required transmission bandwidth and the RF power needed for a given audio quality, making SSB highly efficient for voice communications on congested bands. Typical voice bandwidth is about 2.4 to 3 kHz.

Demodulation requires that the receiver reinsert a carrier using a beat-frequency oscillator (BFO) or a product detector. The reinserted carrier is not a true carrier but a synthesized one, and accurate frequency control is essential for intelligibility. SSB systems rely on precise filtering and stable oscillators; improper tuning can cause distortion or loss of signal quality.

SSB began to be developed and adopted in the mid-20th century and has become the standard for most HF voice communications in amateur, maritime, and aviation services, due to its efficiency compared with conventional AM. Advantages include greater spectral efficiency, better long-distance performance at a given power, and reduced RF bandwidth. Disadvantages include increased transmitter/receiver complexity, sensitivity to frequency and timing inaccuracies, and the need for proper operator tuning and training.

In practice, USB is commonly used on higher frequency bands, while LSB is used on lower bands, though regional practice and equipment can vary. Modern radios and software-defined implementations have mitigated some historical complexities.