AMPLITUDE MODULATION:
When fm =10 Hz and fc= 20Hz;
DSB-SC:
t=0:0.001:1;
vd=8*cos(2*pi*5*t);
vc=0.1*cos(2*pi*15*t);
ft=vc.*vd;
am=ft+vc;
figure(1)
plot(t,vd);
figure(2)
plot(t,vc);
figure(3)
plot(t,am);
FOR DSB-FC :
vm=10 ;
vc=5 ;
fm=20 ;
fc=100 ;
t=0:0.0001:0.0999;
f=1:1:999;
wc=2*pi*fc;
wm=2*pi*fm;
V1=vc+vm*sin(wm*t);
V2=-(vc+vm*sin(wm*t));
Vm=vm*sin(wm*t);
Vc=vc*sin(wc*t);
Vam=(1+sin(wm*t)).*(sin(wc*t));
Vf=abs(fft(Vam,10000))/10000;
figure;
plot(t,Vam);
hold on;
plot(t,V1,'r')
plot(t,V2,'r');
xlabel('frequency'),
ylabel('amplitude');
grid on;
%plotting modulating signal
figure;
plot(t,Vm);
title('AM modulating signal');
xlabel('time'), ylabel('amplitude');
grid on;
%Plot carrier signal
figure;
plot(t, Vc);
title('AM carrier signal');
xlabel('time'), ylabel('amplitude');
grid on;
clear;
FM MODULATION:
vc=1;
vm=1;
fm=250;
fc=5000;
m=10;
t=0:0.00001:0.09999;
f=0:10:99990;
wc=2*pi*fc;
wm=2*pi*fm;
sc_t=vc*cos(wc*t);
sm_t=vm*cos(wm*t);
kf=1000;
s_fm=vc*cos((wc*t)+10*sin(wm*t));
vf=abs(fft(s_fm,10^4))/5000;
figure;
plot(t,s_fm);
hold on;
plot(t,sm_t,'r');
axis([0 0.01 -1.5 1.5]);
xlabel('time(second)'),ylabel('amplitude');
title('FM time-domain');
grid on;
figure;
plot(f,vf);
axis([ 0 10^4 0 0.4]);
xlabel('frequency'),ylabel('amplitude');
title('FM frequency-domain');
grid on;figure;plot(t,sm_t);
axis([0 0.1 -1.5 1.5]);
title('FM modulating signal');
EmoticonEmoticon