- To study and learn the amplitude modulation.
- To learn the MATLAB coding for amplitude modulation.
- To observe the amplitude modulation wave form.
The amplitude modulation is a process in which the amplitude of carrier c(t) is varied about a mean value with the massage signal m(t). Amplitude modulation (AM) is the family of modulation schemes in which the amplitude of a sinusoidal carrier is changed as a function of the modulating message signal.
Let, the massage signal is, m(t)= Amcos (2 πfmt)
And the carrier signal is, c(t)= Accos(2πfct)
So the modulated signal is,
s(t)= Ac cos(2πfct)+ Am cos(2πfmt)
= Ac (1+ka m(t))sin(2πfct)
Here Ac and Am is the amplitude of carrier and message signal fc and fm is the frequency of carrier and message signal and ka is a constant called the amplitude sensitivity of the modulated signal.
k a m ( t ) <1
and f c >> ω m
modulation will be perfect. In amplitude modulation only the amplitude of the
carrier wave is changed in accordance the signal. However the frequency of the
modulated wave remains the same.
1. Mat lab software
Fc= input('Carrier signal Frequency=');
Fm=input('Message Signal Frequency=');
Ac=input('Carrier signal Amplitude=');
Am=input('Message Signal Amplitude=');
title('Amplitude Modulated Signal');
Figure 01: The Carrier Signal, Message Signal and Amplitude Modulated Signal.
1. The carrier frequency
is much greater than the message frequency
2. The amplitude of the carrier and message signal should take the same value.
3. It can send massage without interference.
4. The condition
k a m ( t ) <1
should be satisfied.
Amplitude modulated signals are generated by multiplying message signals with a carrier and adding the carrier to this product. The amplitude of the message signal is varied to produce different values of the modulation index. The MATLAB environment can be an effective tool for viewing the effects of various forms of modulation.