DSbSC

Double sideband suppressed carrier (DSBSC) is a form of amplitude modulation in which the carrier is removed from the transmitted signal, leaving two symmetrical sidebands around the carrier frequency that contain the information. The standard representation for a baseband message m(t) after modulation is s(t) = m(t) cos(ωc t), assuming appropriate scaling and a zero-mean m(t).

Generation of DSBSC is typically accomplished with a balanced modulator or ring modulator that multiplies the baseband signal by a carrier signal. Because the carrier component is canceled in the process, the transmitted spectrum contains only the upper and lower sidebands, each carrying the same information.

Demodulation of DSBSC requires coherent detection. The received signal is multiplied by a locally generated carrier cos(ωc t) (and, if needed, by sin(ωc t) for phase information) and then low-pass filtered to recover m(t). Envelope detection is unsuitable because the carrier is suppressed and the instantaneous amplitude no longer follows the baseband message.

Power and bandwidth considerations differ from conventional AM. DSBSC transmits no carrier power; all available power resides in the two sidebands. The RF bandwidth is twice the baseband bandwidth (two sidebands). This makes DSBSC more power-efficient than standard AM but generally less spectrally efficient than single-sideband (SSB) modulation.

Advantages of DSBSC include improved power efficiency over carrier-based AM and simpler generation using standard modulators. Disadvantages include the need for precise carrier recovery at the receiver and greater sensitivity to phase and frequency errors. DSBSC has historical use in analog radio links and certain data channels, and it remains of interest in discussions of modulation techniques alongside DSB with carrier and SSB.