Double - Sideband Suppressed - Carrier (DSB - SC) Demodulation


To DSB-SC Demodulation & to observe the demodulated wave & its spectrum.


As its name implies, the product detector uses multiplication and so mathematics are necessary to explain its operation. The incoming DSBSC signal is multiplied by a pure sinewave that must be the same frequency as the DSBSC signal's suppressed carrier. This sinewave is generated by the receiver and is known as the local carrier.

To see why this process recovers the message, let's describe product detection mathematically:

DSBSC demodulator's output = the DSBSC signal X the local carrier

Experiment AM Modulation shows how the envelope detector can be used to recover the original message from an AM signal i.e., demodulate it. Unfortunately, the envelope detector cannot be used to demodulate a DSBSC signal.

To understand why, recall that the envelope detector outputs a signal that is a copy of its input's envelope. This works well for demodulating AM because the signal's envelopes are the same shape as the message that produced it in the first place i.e., as long as it's not over¬modulated. However, recall that a DSBSC signal's envelopes are not the same shape as the message.

Instead, DSBSC signals are demodulated using a circuit called a product detector though product demodulator is a more appropriate name and its basic block diagram is shown in Fig.1. Other names for this type of demodulation include a synchronous detector and switching detector.