%%Amplitude modulation ----Single Tone Modulation
%Howard H Ho /3/26/08
%Carrier Amplitude
Ac=1;
%Carrier frequency
Fc=0.4;
%baseband frequency
Fm=0.05;
%sampling
Fs=10;
%%undermodulation
mu=0.5;
t=0:1/Fs:200;
mt=cos(2*pi*Fm*t);
st=Ac*(1+mu*mt).*cos(2*pi*Fc*t);
subplot(2,1,1);
plot(t,st,t,Ac*(mu*mt+ones(1,length(mt))),'r');
title('\mu=0.5 undermodulationAc(1+\mucos(2\pi0.05t))cos(2\pi0.4t)');
xlabel('time (s)');ylabel('amplitude');
st_fft=fft(st);
st_fft=fftshift(st_fft);
st_fft_fre=Fs/2*linspace(-1,1,length(st_fft));
% st_fft=abs(st_fft(1:length(st_fft)/2+1));
% st_fft_fre=[0:length(st_fft)-1]*Fs/length(st_fft)/2;
subplot(2,1,2);
plot(st_fft_fre,abs(st_fft));
title('spectrumside frequency amplitude=carrier frequency amplitude*\mu/2');
xlabel('Frequency (Hz)');axis([-1 1 0 1000*Ac+100]);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%total modulation
figure;
mu=1;
t=0:1/Fs:200;
mt=cos(2*pi*Fm*t);
st=Ac*(1+mu*mt).*cos(2*pi*Fc*t);
subplot(2,1,1);
plot(t,st,t,Ac*(mu*mt+ones(1,length(mt))),'r');
title('\mu=1 total modulationAc(1+\mucos(2\pi0.05t))cos(2\pi0.4t)');
xlabel('time (s)');ylabel('amplitude');
st_fft=fft(st);
st_fft=fftshift(st_fft);
st_fft_fre=Fs/2*linspace(-1,1,length(st_fft));
subplot(2,1,2);
plot(st_fft_fre,abs(st_fft));
title('spectrumside frequency amplitude=carrier frequency amplitude*\mu/2');
xlabel('Frequency (Hz)');axis([-1 1 0 1000*Ac+100]);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%overmodulation
figure;
mu=2;
t=0:1/Fs:200;
mt=cos(2*pi*Fm*t);
st=Ac*(1+mu*mt).*cos(2*pi*Fc*t);
subplot(2,1,1);
plot(t,st,t,Ac*(mu*mt+ones(1,length(mt))),'r');
title('\mu=2 overmodulationAc(1+\mucos(2\pi0.05t))cos(2\pi0.4t)');
xlabel('time (s)');ylabel('amplitude');
st_fft=fft(st);
st_fft=fftshift(st_fft);
st_fft_fre=Fs/2*linspace(-1,1,length(st_fft));
subplot(2,1,2);
plot(st_fft_fre,abs(st_fft));
title('spectrumside frequency amplitude=carrier frequency amplitude*\mu/2');
xlabel('Frequency (Hz)');axis([-1 1 0 1000*Ac+100]);