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

Explanation

(a) When a modulating AF weve is super imposed on a high frequency carrier weve in a
manner that the freaquency of modulated weve is same as that of the carrier weve but its
amplitude is made proportional to the instantaneous amplited of the audio frequency
modulating voltage process is called Amplitude Modulation
(b) `f_(LSB)= f_(c) - f_(m) = 640kHz`
`f_(USB)= f_(c) + f_(m) = 640kHz`
Adding `2f_(c) = 130 kHz So, f_(c) = 650kHz`
Subtracting `2f_(m) = 20 kHz f_(m) = 10 kHz`
Band width `2xx` frequency of modulating signal = ` 2 xx 10 kHz = 20 kHz.`