Notes

1. To study the function of amplitude Modulation and
Demodulation using MATLAB.

2. To study the amplitude modulation in 3 signals in
MATLAB.

3. To study the working of DSB-SC modulator and
demodulator using MATLAB.

4. To study and generate single sideband (SSB)
modulation using MATLAB.

5. To study and generate frequency modulation and
demodulation using MATLAB.

6. To study sampling theorem and its reconstruction
or reconstitution using MATLAB

7. To verify sampling theorem with continuous signal
using MATLAB software.

8. To study pulse amplitude modulation and
demodulation techniques using MATLAB.

9. To study pulse width modulation and
demodulation technique using MATLAB software.





1.
% carrier Frequency
Fc = 200;
% sampling frequency
Fs = 4000;
% time duration
t = (0 : 1 / Fs : 1);
%sine wave with time duration of
x=sin(2*pi*t);
%amplitude Modulation
y = ammod(x, Fc, Fs );
plot(y);
title('Amplitude Modulation );
xlabel('Time(sec)')
ylabel('Amplitude')
2.
Ac = input('enter carrier signal amplitude: ');
Am = input('enter message signal amplitude: ');
fc = input('enter carrier frequency: ');
fm = input('enter message frequency: '); % fm < fc
m = input('enter modulation index: ');
t = input('enter time period: ');
t1 = linspace(0, t, 1000);
y1 = Am * sin(2 * pi * fm * t1); % message signal
y2 = Ac * sin(2 * pi * fc * t1); % carrier signal
eq = (1 + m * y1) .* y2; % element-wise multiplication
subplot(3, 1, 1);
plot(t1, y1);
xlabel('Time');
ylabel('Amplitude');
title('Message signal');
subplot(3, 1, 2);
plot(t1, y2);
xlabel('Time');
ylabel('Amplitude');
title('Carrier signal');
subplot(3, 1, 3);
plot(t1, eq, 'r');
xlabel('Time');
ylabel('Amplitude');
title('Modulated Signal');
3.
close all
clear all
clc
fs = 8000;
fm = 20;
fc = 50;
Am = 1;
Ac = 1;
t = (0:0.1*fs)/fs;
subplot(5,1,1);
ml = Am*cos(2*pi*fm*t);
plot(t, ml);
title("SSB-SC Modulation Demodulation ","Message Signal");
m2 = Am*sin(2*pi*fc*t);
subplot(5,1,2)
cl = Ac*cos(2*pi*fc*t);
plot(t, cl)
title('Carrier Signal')
c2 = Ac*sin(2*pi*fc*t)
subplot(5,1,3)
Susb = 0.5*ml.*cl + 0.5*m2.*c2;
plot(t, Susb)
title('SSB-SC Signal with USB');
subplot(5,1,4)
Slsb = 0.5*ml.*cl + 0.5*m2.*c2;
plot(t, Slsb)
title('SSB-SC Signal with LSB')
r = Susb.*cl;
subplot(5,1,5);
[ba] = butter(1, 0.0001);
mr = filter(ba, 1, r);
plot(t, mr);
title('Demodulated Output')
4.
close all
clear all
fs = 80000;
fm = 1000;
Am = 1;
t = (0:0.01*fs)/fs;
m1 = Am*cos(2*pi*fm*t);
subplot(5,1,1)
plot(t, m1)
title(Message Signal");
fc = 20000;
Ac = 1;
cl = Ac*cos(2*pi*fc*t);
subplot(5,1,2)
plot(t, cl)
title('Carrier Signal');
Susb = 0.5*m1.*cl;
subplot(5,1,3)
plot(t, Susb)
title('SSB-SC Signal with USB');
Slsb = 0.5*m1.*conj(cl);
subplot(5,1,4)
plot(t, Slsb)
title('SSB-SC Signal with LSB');
r = Susb.*cl;
[b, a] = butter(1, 0.0001);
mr = filter(b, a, r);
subplot(5,1,5)
plot(t, mr)
title('Demodulated Output');
5.
close all
clear all
clc
%fm=35Hz, fc=500Hz, Am=1V, Ac=1V, B=10
fs = 10000;
Ac = 1;
Am = 1;
fm = 35;
fc = 500;
B = 10;
t = (0:.1*fs)/fs
wc = 2*pi*fc;
wm = 2*pi*fm;
m_t = Am*cos(wm*t);
subplot(4,1,1);
plot(t,m_t);
title('Modulating or Message signal(fm=35Hz)');
c_t = Ac*cos(wc*t)
subplot(4,1,2);
plot(t,c_t);
title('Carrier signal(fm=500Hz)');
s_t = Ac*cos((wc*t)+B*sin(wm*t));
subplot(4,1,3);
plot(t,s_t);
title('Modulated signal');
d = demod(s_t,fc,fs,'fm');
subplot(4,1,4);
plot(t,d);
title('demodulated signal')
6.
%program for verification of sampling theorem
close all;
clear all;
clc
t=-10:.01:10;
T=4;
fm=1/T;
x=cos(2*pi*fm*t);
subplot(2,2,1);
plot(t,x);
title("Sampling Theorem");
%input signal
xlabel('time');ylabel('x(t)');title('continous time signal');
grid;
n1=-4:1:4;
fs1=1.6*fm;
fs2=2*fm;
fs3=8*fm;
%discrete time signal with fs<2fm
x1=cos(2*pi*fm/fs1*n1);
subplot(2,2,2);
stem(n1,x1);
xlabel('time');ylabel('x(n)');
title('discrete time signal with fs<2fm');
hold on
subplot(2,2,2);
plot(n1,x1)
grid;
%discrete time signal with fs=2fm
n2=-5:1:5;
x2=cos(2*pi*fm/fs2*n2);
subplot(2,2,3);
stem(n2,x2);
xlabel('time');ylabel('x(n)');
title('discrete time signal with fs=2fm');
hold on
subplot(2,2,3);
plot(n2,x2);
%discrete time signal with fs>2fm
grid;
n3=-20:1:20;
x3=cos(2*pi*fm/fs3*n3);
subplot(2,2,4);
stem(n3,x3);
xlabel('time');ylabel('x(n)');
title('discrete time signal with fs>2fm');
hold on
subplot(2,2,4);
plot(n3,x3);
grid;
7.
clc;
T=0.04; % Time period of 50 Hz signal
t=0:0.0005:0.02;
f = 1/T;
n1=0:40;
size(n1)
xa_t=sin(2*pi*2*t/T);
subplot(2,2,1);
plot(200*t, xa_t);
title('verification of sampling theorem');
title('continuous signal');
xlabel('t');
ylabel('x(t)');
ts1=0.002;%>niq rate
ts2=0.01;%=niq rate
ts3=0.1; %<niq rate
n=0:20;
x_ts1=2*sin(2*pi*n*ts1/T);
subplot(2,2,2);
stem(n,x_ts1);
title('greater than Nq');
xlabel('n');
ylabel('x(n)');
n=0:4;
x_ts2=2*sin(2*pi*n*ts2/T);
subplot(2,2,3);
stem(n,x_ts2);
title('Equal to Nq');
xlabel('n');
ylabel('x(n)');
n=0:10;
x_ts3=2*sin(2*pi*n*ts3/T);
subplot(2,2,4);
stem(n,x_ts3);
title('less than Nq');
xlabel('n');
ylabel('x(n)');
8.
% pulse amplitude modulation
close all
clear all
clc
t = 0: 1/1e3 : 10; %1 kHz sample freq for 1s
d = 0: 1/5 : 10;
x = 5+sin(2*pi/4*2*t); %message signal
figure;
subplot(3,1,1)
plot(x)
title('Message');
xlabel('time');ylabel('amplitude');
y = pulstran(t,d,'rectpuls',0.1); %generation of pulse input
subplot(3,1,2)
plot(y);
title('Pulse Input');
xlabel('time');ylabel('amplitude');
z=x.*y; %PAM output
subplot(3,1,3);
plot(z);
title('PAM modulation');
xlabel('time');ylabel('amplitude');
9.
%pulse width modulation and demodulation
close all
clear all
clc
fc = 1000;
fs = 10000;
fl = 200;
t = 0:1/fs:((2/fl)-(1/fs));
xl = 0.4*cos(2*pi*fl*t)+0.5;
%modulation
yl = modulate(xl, fc, fs, 'pwm');
subplot(311);
plot(xl);
axis([0 50 0 1]);
title('Original signal taken message, f1=500, fs=10000');
subplot(312);
plot(yl);
axis([0 500 -0.2 1.2]);
title('PWM')
%demodulation
xl_recov = demod(yl, fc, fs, 'pwm');
subplot(313);
plot(xl_recov);
title('time domain recovered, single tone, f1=200')
axis([0 50 0 1]);