I would like to have the frequency power spectrum of a square wave.

The duration of one wave (T/2) is 0.1 ms. Only the positive part is used. However the amount of squares also varies from 1 to 30 Hz.

So I would like to compare the spectral densities of 30 Hz and 1 Hz squarewaves, in which each square has a duration of 0.1 ms.

Could anyone tell me how to do this.

 

If you have the data, you can take the DTFT (discrete time fourier transform) of it in matlab for example. And analyze the different waveforms you get.

 

There are fourier transform pairs that will help you get the frequency spectrum. From there the spectral density is something related to the integral of the frequency spectrum in a certain band. Since the square wave is the sum of discrete frequencies, the spectral density can be rewritten as a sum instead of an integral.