Which modulation technique is characterized by suppressed-carrier DSB, requiring carrier recovery?

• A. AM does not include the carrier.
• B. DSB has a carrier.
• C. DSB-SC has no carrier but is not efficient.
• D. DSB-SC is suppressed-carrier DSB, improving efficiency but requiring carrier recovery at the receiver.

Answer: (D)

Suppressed-carrier DSB transmits energy only in the two sidebands; there is no carrier energy present. Because there’s no carrier reference in the received signal, you can’t simply envelope-detect to recover the original audio. Instead, the receiver must recreate or recover a carrier at the same frequency and with the correct phase to perform coherent demodulation. This carrier recovery step is what makes DSB-SC both more power-efficient (more of the transmitter’s power goes into the useful sidebands rather than a carrier) and more demanding to implement at the receiver. In contrast, standard AM includes a carrier, so envelope detection works without any carrier recovery, and a plain DSB with carrier clearly has a carrier present.