Test: Angle Modulation - Electronics and Communication Engineering (ECE) MCQ

Explanation:
Frequency modulation is a method of encoding information on a carrier wave by varying its frequency. In FM, the frequency of the carrier wave is varied in proportion to the amplitude of the modulating signal. This variation in frequency is what allows the transmission of information.
To understand why the frequency shift in FM is directly proportional to the amplitude of the modulating signal, let's break down the process:
1. Modulating Signal: The modulating signal is the signal that carries the information to be transmitted. It can be an audio signal, such as a voice or music, or any other type of signal.
2. Frequency Deviation: In FM, the frequency of the carrier wave is shifted above and below its center frequency. The extent of this frequency shift is known as the frequency deviation. It determines the range of frequencies that the carrier wave can vary.
3. Amplitude of the Modulating Signal: The amplitude of the modulating signal directly affects the frequency deviation in FM. When the amplitude of the modulating signal increases, the frequency deviation also increases.
4. Direct Proportionality: The relationship between the amplitude of the modulating signal and the frequency shift can be described as direct proportionality. This means that as the amplitude of the modulating signal increases, the frequency shift also increases proportionally. Similarly, if the amplitude decreases, the frequency shift will decrease accordingly.
In summary, the amount of frequency shift in FM is directly proportional to the amplitude of the modulating signal. This relationship allows for the transmission of information through varying frequencies, with the amplitude of the modulating signal determining the extent of the frequency shift.the change in the amplitude of modulating signal value.

According to Carson’s rule, the bandwidth of a single-tone wideband FM is
BW = 2(Δω + ω_m)

• In FM, the frequency deviation is proportional only to the amplitude variation of the modulating signal and it is independent of modulating frequency fm. Hence, statement-1 is not correct.
• In PM, the frequency deviation increases with increase in modulating frequency fm and decreases with decrease in modulating frequency. Thus, frequency deviation in PM is proportional to modulating frequency. Hence, statement-2 is false.
• Statement-3 is correct.
• it is possible to receive FM on a PM receiver and PM on a FM receiver. Hence, statement-4 is correct.
• Signal to noise ratio of PM is inferior to that in FM. Hence, statement-5 is not correct.

A PM wave can be generated using a frequency modulator as shown in figure below:

The noise immunity of FM is better than AM and PM while the noise immunity of PM is better than AM but worse than FM.

Given, v = 10sin [5 x 10⁸t + 4 sin 1250 t] 
Comparing the above equation with the standard for FM given by


we have modulating frequency,

and modulation index,
m_f = 4
∴ Maximum deviation,

Given, 
We know that,

or,

When, V'_m = 4 V, the new deviation in frequency is