Question

The frequencies of two side bands in an AM wave are 640 kHz and 660 kHz respectively. Find the frequencies of carrier and modulating signal. What is the bandwidth required for amplitude modulation?

Answer 1

Let frequency of carrier wave be f_c and frequency of modulating wave be f_m
f_c+ f_m = 660 kHz ....... (i)

f_c− f_m = 640 kHz ....... (ii)

Solving (i) and (ii), we get

2 f_c = 1300

⇒ f_c = 650 kHz

Now,

f_c+ f_m = 660 kHz

650+ f_m = 660 kHz

⇒f_m = 10 kHz

We know,

Bandwidth = 2×f_m = 20 kHz

Hence,
Frequency of carrier signal is 650 kHz
Frequency of modulating signal is 10 kHz
Bandwidth required for amplitude modualtion is 20 kHz