Question

A message signal of frequency 20 KHz and peak voltage of 20 volts is used to modulate a carrier signal of frequency 2 MHz and peak voltage of 40 volts. Determine (i) modulation index, (ii) the side bands produced. Draw the corresponding frequency spectrum of amplitude modulated signal.

Answer 1

Given

For message signal

Frequency, $f_m=20kHz$

Peak voltage, $A_m=20V$

For carrier frequency

Frequency, $f_c=2MHz=2000kHz$

Peak voltage, $A_c=40V$

(i) Modulation frequency is given by

$\mu =\frac{A_m}{A_c}=\frac{20}{40}=0.5$

(ii) The side band will be at $(f_c\pm f_m)=(2000\pm 20)kHz=2020kHzand1980kHz$