A modulating signal is a square wave, as shown in Fig. 15.14.


The carrier wave is given by c (t) = 2sin(8πt) volts.


(i) Sketch the amplitude modulated waveform


(ii) What is the modulation index?


It can be observed from the given modulating signal that the amplitude of the modulating signal, Am = 1 V


It is given that the carrier wave c (t) = 2sin(8πt) volts


Amplitude of the carrier wave, Ac = 2 V


Time period of the modulating signal Tm = 1 s


The angular frequency of the modulating signal is calculated as:


(t)m = 2π/Tm


= 2π rad s-1 (as Tm = 1)……………….(i)


The angular frequency of the carrier signal is calculated as:


(t)m = 8π rad s-1 ……….(ii)


From equations (i) and (ii), we get:


(t)m = 4(t)c


The amplitude modulated waveform of the modulating signal is shown in the following figure.



(ii) Modulation index,


m = Am/Ac = 1/2 = 0.5


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