% AM program on April 10, 2007
% message is a sinusoid
    mu=0.5;
    fm=0.05;
    fc=0.4;
    T=200;
    Ts=0.1
    t=[0: Ts: T-Ts];
    N=T/Ts;
% AM signal    
    m=mu*cos(2*pi*fm*t);
    s=(1+m).*cos(2*pi*fc*t);
%    
     z0=fft(s);
     zz0=fftshift(z0); % fftshift lets center to be 0 Hz
     Ts=t(2)-t(1);  % the sampling period
     Fs=1/Ts;       % the sampling frequency in Hz
     F = Fs*(-N/2:(N/2)-1)/N;   % frequency axis
%   (abs(z0));
    plot(F, abs(zz0));
    i1=1065;
    i2=1095;
    % this is a magnified spectrum
    % If you want to see, then delete the comment command %
%    plot(F(i1:i2), abs(zz0(i1:i2)))