Which statement correctly contrasts DSB-SC with conventional AM in terms of carrier presence and receiver demodulation?

Which statement correctly contrasts DSB-SC with conventional AM in terms of carrier presence and receiver demodulation?

• A. DSB-SC includes a carrier, making demodulation straightforward.
• B. DSB-SC has no carrier and requires carrier reinsertion at the receiver; AM includes a carrier; easier to demod.
• C. AM has no carrier and requires carrier reinsertion; DSB-SC includes a carrier; demod harder for AM.
• D. DSB-SC and AM both include a carrier and have identical demod challenges.

Answer: (B)

The key idea is how the carrier presence (or absence) affects how you recover the original signal. In DSB-SC, there is no unmodulated carrier transmitted; information sits in the two sidebands. To demodulate, you must recreate a carrier at the receiver and perform coherent detection (carrier reinsertion followed by multiplication and low-pass filtering). Envelope detection won’t work because there’s no carrier to form an envelope. In conventional AM, a carrier is transmitted along with the sidebands. The envelope of the received signal follows the modulating signal (when modulation is not over 100%), so a simple envelope detector or product detector can recover the message easily without needing a synchronized local carrier. So the statement that correctly contrasts them says: DSB-SC has no carrier and requires carrier reinsertion at the receiver; AM includes a carrier; easier to demod. The other options misstate whether a carrier is present or the ease of demodulation.

The key idea is how the carrier presence (or absence) affects how you recover the original signal. In DSB-SC, there is no unmodulated carrier transmitted; information sits in the two sidebands. To demodulate, you must recreate a carrier at the receiver and perform coherent detection (carrier reinsertion followed by multiplication and low-pass filtering). Envelope detection won’t work because there’s no carrier to form an envelope.

In conventional AM, a carrier is transmitted along with the sidebands. The envelope of the received signal follows the modulating signal (when modulation is not over 100%), so a simple envelope detector or product detector can recover the message easily without needing a synchronized local carrier.

So the statement that correctly contrasts them says: DSB-SC has no carrier and requires carrier reinsertion at the receiver; AM includes a carrier; easier to demod. The other options misstate whether a carrier is present or the ease of demodulation.