Question

To save transmitted power, the carrier of an AM signal obtained by sinusoidal modulation to a depth of modulation equal to 1, has been recovered. The percentage saving in power is________.

• A. 33.33
• B. 50
• C. 66.66
• D. 100

Hint:

In 100 percent modulated AM, removing carrier saves \( \approx 66.66% \) power. Only sidebands carry info!

Answer 1

The Correct Option is C

In conventional AM transmission:
- Power is shared among carrier and sidebands.
- For 100% modulation (modulation index \( m = 1 \)):
- Carrier power = \( P_c \)
- Total power = \( P_c (1 + \frac{m^2}{2}) = P_c (1 + 0.5) = 1.5P_c \)
- Sideband power = \( 0.5P_c \)
If the carrier is suppressed (as in DSB-SC), power = only sidebands = \( 0.5P_c \). Hence, power saved = \( 1.5P_c - 0.5P_c = P_c \)
Percentage saved: \[ \frac{P_c}{1.5P_c} \times 100 = 66.66% \]