Single-sideband modulation: Difference between revisions

Revision as of 21:40, 12 November 2002

Revision as of 21:18, 15 March 2003

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'''Single -sideband modulation''' (SSB) is a refinement of the technique of [[amplitude modulation]] designed to be more efficient in its use of power and [[bandwidth]]. It is closely related to '''vestigial -sideband modulation''' ('''VSB''') (see below).

Amplitude modulation typically produces a modulated output signal that has twice the bandwidth of the modulating signal, with a significant power component at the original carrier frequency. Single -sideband modulation improves this, at the cost of extra complexity.

The best way of thinking of SSB modulation is to first consider an amplitude modulated signal. This will have two frequency-shifted copies of the modulated signal (the lower one is frequency-inverted) on either side of the remaining carrier signal.

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To produce an SSB signal, apply a filter that will filter out one of the sidebands, and remove the carrier signal. What remains still contains the entire information content of the AM signal, using substantially less bandwidth and power, but cannot now be demodulated by a simple envelope detector.

When the 'wrong' subcarrier is only partially suppressed, the resulting modulation technique is known as [[vestigial -sideband modulation]] ('''VSB''').

To recover the original signal from an SSB signal, the carrier must be replaced with an extra 'false carrier' signal, prior to sending the signal to a standard envelope detector.