Question

Calculate the power in one of the sidebands in SSBSC modulation when the carrier power is 124 W, and there is 80% modulation depth in the amplitude modulated signal.
A. 89.33 W
B. 64.85 W
C. 79.36 W
D. 102 W

Answer 1

Hint:If a signal has to transmit from one station to another, the signal should have a frequency above 20 kHz. The advantage of choosing high frequency is that it can transmit over a long distance with minimum power. So, to convert the low-frequency audio signal to a high frequency, audio signals will superimpose on a high-frequency electrical wave. This high-frequency wave is known as the carrier wave or carrier signal. The resultant wave after superimposing is known as the modulated wave, and the process is called modulation.

Complete step by step answer:
Given:
The modulation index is m = 0.8.
The carrier power is $P_C$ = 124 W
We know that the power in sidebands $P$ is calculated as:
$$P=m^2{P}_C/4$$
We will now substitute m=0.8, $P_c$ = 124 W to find P.
$$\Rightarrow P={0.4}^2\times 124\mathrm{W}/4$$
$$\Rightarrow P=79.36\mathrm{W}$$
Therefore, the power in one of the sidebands in SSB SC modulation is 79.36 W.

the correct option is (C).

Additional information:Modulation factor is the ratio of change in amplitude of the carrier wave after modulation to the amplitude of the carrier wave before modulation. The modulation factor decides the strength and quality of a transmitting signal. If the modulation factor is greater than unity, the variation of the carrier amplitude is small. Hence the signal will be weak. If the modulation factor is greater than unity, the signal that has to be transmitted gets distorted, and as a result, the signal wave cannot be reproduced properly. For a successful modulation, the degree of modulation should not exceed 100 %.

Note:In this SSBSC method of transmission, one of the sidebands (either upper sideband or lower sideband) is sent. Carrier and the other sideband are suppressed to reduce the power wastage.