Amplitude_Modulation.m

clc;
close all;
clear all;

% Modulating index
m_critical = 1; %critical
m_over = 1.5; %over
m_under = 0.5; %under 

% Amplitude of modulating signal
Am = 10; 

% Frequency of modulating signal (Hz)
fm = 5; 

% Time period of modulating signal (s)
Ta = 1/fm; 
t = 0:(Ta/1000):1;

% Modulating signal
ym = Am*cos(2*pi*fm*t);
figure(1)
subplot(4,1,1)
plot(t,ym)
grid on;
xlabel('Time Index')
ylabel('Amplitude')
title('Modulating Signal')

% Relation between Am/Cm and fc/fa
Ac = Am/m_critical; %Change in modulation index
fc = fm*15; %Relationship equation
Tc = 1/fc;

% Carrier signal
yc = Ac*cos(2*pi*fc*t);
subplot(4,1,2)
plot(t,yc)
grid on;
xlabel('Time Index')
ylabel('Amplitude')
title('Carrier Signal')

% Amplitude Modulation
y_mod = (Ac+ym).*cos(2*pi*fc*t);
subplot(4,1,3)
plot(t,y_mod)
grid on;
xlabel('Time Index')
ylabel('Amplitude')
title('Amplitude Modulated Signal')


%Amplitude Demodulation
y_demo = y_mod.*yc;
[b,a] = butter(5,0.01); 
y_demo_filtered = filter(b,a,y_demo);
subplot(4,1,4)
plot(t,y_demo_filtered);
grid on;
xlabel('Time Index')
ylabel('Amplitude')
title('Demodulation after filter application')