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Question:

A carrier wave of peak voltage 14 V is used for transmitting a message signal. What is the peak voltage of the modulating signal given to achieve a modulation index of 80%?

7 V

22.4 V

11.2 V

28 V

Solution:

The correct option is 11.2 V

Since
Modulation Index = Vm / Vc
where:
Vm = Modulating Signal Voltage
Vc = Carrier Signal Voltage

0.8 = Vm / 14
Vm = 11.2 V