4.4-3 A modulating signal m(t) is given by: \text { (a) } m(t)=\cos 100 \pi t+2 \cos 300 \pi t \text { (b) } m(t)=\sin 100 \pi t \sin 500 \pi t In each case: (i) Sketch the spectrum of m(t). \text { (ii) Find and sketch the spectrum of the DSB-SC signal } 2 m(t) \cos 1000 \pi t (iii) From the spectrum obtained in part (ii), suppress the LSB spectrum to obtain the USB spectrum. (iv) Knowing the USB spectrum in part (ii), write the expression Pusb (t) for the USB signal. (v) Repeat parts (iii) and (iv) to obtain the LSB signal sp (1) in both time and frequency domains.

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