Define and differentiate between AM, DSB, and DSB-SC.

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

Answer: (D)

Understanding how the carrier is handled in modulation explains the differences between AM, DSB, and DSB-SC. In conventional AM, the carrier is transmitted along with two sidebands; energy is spent on the carrier that doesn’t carry information, which is why envelope-detection at the receiver works but overall transmitter efficiency is not optimal.

In double sideband with carrier, you still have the carrier present along with the sidebands. In double sideband suppressed-carrier, the carrier is removed, so the transmitted signal consists only of the two sidebands. This improves transmitter efficiency because less power is wasted on the carrier, but it requires the receiver to recover or synthesize a carrier locally to perform coherent demodulation; without a carrier reference, demodulating the signal is not straightforward.

The statement DSB-SC is suppressed-carrier DSB, improving efficiency but requiring carrier recovery at the receiver accurately captures this trade-off between efficiency and receiver complexity, making it the correct description.