GATE EC 2020 Set 1 — Question 57
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Communications → Analog Communications → Angle Modulation (FM & PM)
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Question
and as defined below, are the phase modulated and the frequency modulated waveforms, respectively, corresponding to the message signal shown in the figure.andwhere is the phase deviation constant in radians/volt and is the frequency deviation constant in radians/second/volt. If the highest instantaneous frequencies of and are same, then the value of the ratio is ______ seconds.

Correct answer
2 to 2
Solution
For Phase Modulation (PM):
The instantaneous phase is .
The instantaneous frequency is .
From the graph of , the maximum positive slope occurs for :
V/s.
Thus, the highest instantaneous frequency for PM is .For Frequency Modulation (FM):
The instantaneous phase is .
The instantaneous frequency is .
The maximum value of is V.
Thus, the highest instantaneous frequency for FM is .Given :
.
The instantaneous phase is .
The instantaneous frequency is .
From the graph of , the maximum positive slope occurs for :
V/s.
Thus, the highest instantaneous frequency for PM is .For Frequency Modulation (FM):
The instantaneous phase is .
The instantaneous frequency is .
The maximum value of is V.
Thus, the highest instantaneous frequency for FM is .Given :
.
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