Question

When the modulating frequency is doubled, the modulation index is halved and the modulating voltage remains constant, the modulation system is

• A. Amplitude modulation
• B. Phase modulation
• C. Frequency modulation
• D. All of these

Answer 1

The correct option is C

Frequency modulation

Explanation for correct options :

option C:

1. Frequency modulation is a technique for encoding information on a particular signal by varying the frequency of carrier wave in accordance with the frequency of modulating signal.
2. The modulation index of amplitude modulation is defined as the measure of the extent of amplitude variation about an unmodulated carrier.
3. Since the modulating frequency is varied instantaneously, the information in the signal is encoded and it is called frequency modulation.
4. In frequency modulation, the carrier wave has constant amplitude and the modulating wave information is conveyed by the amplitude of the carrier.
5. Hence the change in the modulating frequency and index does not vary the amplitude of the signal thereby maintaining the modulating voltage constant. Hence, Frequency modulation is the type of modulation taking place.
6. Frequency modulation is done to reduce the noise and improve the quality of the radio signal.

Explanation for incorrect options :

Option A:

Amplitude Modulation: AM is a process by which the wave signals is transmitted by modulating the amplitude of signal.

Option B:

Phase modulation is a process of a modulation pattern for conditioning communicating signal for transmission.

Hence, option C is the right answer.