visualizing the fourier transform of pseudo random sequence with Matlab

Hello,

I'm trying to visualize the fourier transform of a pseudo random sequence with Matlab, and I'm struggling with "sampling" the sequence with enough samples to display a very noticeable sinc response..any suggestions on how to do this?

thanks! Jorge

Answer 1

[Wayne King]

By pseudo random sequence do you mean a white noise sequence created with something like randn()? If so, why would that have a sinc-shaped response in the Frequency domain?

To illustrate a sinc-shaped response, you can do something like this:

h = 1/10*ones(10,1);
plot(abs(fftshift(fft(h,64))))

[Jorge Rivé]

Hi Wayne,

I don't think I asked the question entirely correctly. I'm a newbie to signal processing... I want to see what the Fourier Transform of a a 127-bit (or 128), PRBS (basically a rectangular pulse train with constant bit period but varying duty cycle) would look like, for example.

I expect a sync response due to the rectangular pulses,and since the sequence repeats every 127 cycles, I expect the response to be discrete frequencies (fourier series).

Ultimately, what I want to play with is sampling the sequence at a rate which is not an integer multiple of the minimum pulse width of the sequence, so I can see how I can manipulate where the frequency bins lie and thus reduce the aliasing (not sure I explained this all that well).....