how to find max freq and lamdha min for a pulse

 hi all
i want to know how can i calculate max frequency and min wavelength for following function
y=15(1-cos(2 *pi*f*t/n)*sin(2*pi*f*t)
here f=0.5MHz
n=5cycle 
      the matlab coding which i did is
> f=0.5e6;
> fs=f*100;
> ts=1/fs;
> n=5
> t=0:ts:n/f;
> y=15*(1-cos(2*pi*f*t/n)).*cos(2*pi*f*t);
>plot (t,y)
>x=fft(y);
>plot(x);
now what should i do further......plz help me

Answer 1

[Wayne King]

   ydft = fft(y);
   ydft = ydft(1:floor(length(ydft)/2)+1);
   [maxval,I] = max(abs(ydft));
   freq = 0:fs/length(y):fs/2;
   fprintf('Maximum at %2.3f Hz\n.', freq(I));

You would have been better with:

   t=0:ts:n/f-ts;
   y=15*(1-cos(2*pi*f*t/n)).*cos(2*pi*f*t);
   ydft = fft(y);
   ydft = ydft(1:length(ydft)/2+1);
   [maxval,I] = max(abs(ydft));
   freq = 0:fs/length(y):fs/2;
   fprintf('Maximum at %2.3f Hz\n.', freq(I));

Due to the spacing of the frequencies in the DFT. As far as the wavelength, you have not told us the propagation speed, which you have to in order to determine wavelength. If we assume that it is the speed of light, then

lambda = 3e8/freq(I);
fprintf('Wavelength is %3.2f meters.\n',lambda)