single sideband

(communications) Pertaining to single-sideband communication. Abbreviated SSB.

An electronic signal-processing technique in which a spectrum of intelligence is translated from a zero reference frequency to a higher frequency without a change of frequency relationships within the translated spectrum. Single-sideband (SSB) signals have no appreciable carrier.

Amplitude-modulated (AM) signals have identical upper and lower sidebands symmetrically located on each side of the translation frequency, which is often called the carrier. The SSB spectrum differs from the AM spectrum in having little or no carrier and only one sideband. See also Amplitude modulation.

In the SSB signal-processing action, the intelligence spectrum to be translated is applied to the signal input port of a balanced modulator. A higher-frequency sinusoidal signal, often called a carrier, is applied to the other input port of this circuit. Its function is to translate the zero reference spectrum to the carrier frequency and to produce the upper and lower sidebands, which are symmetrically located on each side of the carrier. The carrier frequency power is suppressed to a negligible value by the balanced operation of the modulator and does not appear at the output. Generally, the balanced modulator operates at an intermediate frequency which is lower than the frequency of transmission. Following the balanced modulator is a sideband filter which is designed to remove the unwanted sideband signal power and to allow only the desired intelligence spectrum to pass. See also Amplitude modulator; Modulator.

There are many advantages in the use of SSB techniques for communication systems. The two primary advantages are the reduction of transmission bandwidth and transmission power. The bandwidth required is not greater than the intelligence bandwidth and is one-half that used by amplitude modulation. The output power required to give equal energy in the intelligence bandwidth is one-sixth that of amplitude modulation.

Propagation of radio energy via ionospheric refraction provides the possibility for multiple paths of differing path length which can cause a selective cancellation of frequency components at regular frequency spacings. This produces in amplitude modulation a severe distortion of the intelligence because of the critically dependent carrier-to-sideband amplitude and phase relationships. SSB is much less affected under these conditions.

The upper or lower sideband of a carrier frequency that is amplitude modulated. To save power, the carrier and one of the sidebands is eliminated, leaving only a single sideband for transmission. Single sideband is used mostly in amateur radio (ham radio). See sideband.

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