Question: Q. 10. A sinusoidal carrier wave of amplitude Ac and angular frequency ωc is modulated in accordance with a sinusoidal information signal of amplitude Am and angular frequency ωm. Show that the amplitude modulated signal contains three frequencies centered around ωc. Draw the frequency spectrum of the resulting modulated signal.

[CBSE -SQP-2018]

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Solution:

Ans. The modulated signal :

Cm(t)=(Ac+Amsinωmt)sinωct =Ac(1+AmAcsinωmt)sinωct Cm(t)=Acsinωct+μAcsinωmtsinωct Cm(t)=Acsinωct+μAc2cos(ωcωm)tμAc2cos(ωcωm)t

Frequency Spectrum :

[CBSE Marking Scheme, 2018]



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