%
%               fft_code.m
%
%  This code computes the FFT of a signal comprised of 50 Hz
%  and 120 Hz components sampled at a rate of 1000 Hz (hence
%  dt = 1/1000).  The vector Pyy contains the power spectrum
%  which provides a measure of the energy at the various frequencies.
%

  dt = 1/1000;
  t = 0:dt:0.6;
  x = sin(2*pi*50*t) + sin(2*pi*120*t);
  y = x + 1*randn(size(t));

  f = 1000*(0:255)/512;
  Y = fft(y,512);
  Pyy = Y.*conj(Y)/512;

  figure(1)
  plot(t,y)
  xlabel('Time (s)')
  ylabel('Amplitude (m)')


  figure(2)
  plot(f,Pyy(1:256))
  xlabel('Frequency (Hz)')
  ylabel('Power spectrum')

%
% End of fft_code.m
%