A transmitter with a carrier frequency of 72 MHz is amplitud

A transmitter with a carrier frequency of 7.2 MHz is amplitude-modulated by two tones, one at 1500 Hz, the other at 3000 Hz. What frequencies are produced at the output of the transmitter?

Solution

m(t)= cos (2pi*1500t)+ cos (2pi*3000t)

carrier c(t) = cos (2pi*7.2*10^6t)

s(t) = m(t)*c(t)

      = cos 2pi*(7200000+1500)t + cos 2pi*(7200000-1500)t + cos 2pi*(7200000+3000)t +cos 2pi*(7200000+3000)t

       = cos 2pi*(7201500)t + cos 2pi*(7198500)t + cos 2pi*(7203000)t+cos 2pi*(7197000)t

        frequencies at output = 7201500, 7198500, 7203000, 7197000 Hz