Frequency spectrum

how can i something by fft like in this image?

link : http://imageshack.us/photo/my-images/841/ekil2.jpg/

please help me

[Rick Rosson]

What have you tried so far?

Answer 1

[Rick Rosson]

The best way to start is to specify a value for T, which represents half of the period of the square wave message signal m(t). Then, you will want to specify an appropriate value for the sampling rate Fs, which needs to be large enough to represent several of the harmonics of the square wave in the frequency domain. In other words, choose Fs so that it is quite a bit larger then 1/T, the fundamental frequency.

Once you have defined T and Fs, you will need to define the square wave message signal m(t) in the time domain. There are several ways to accomplish this task in MATLAB. After you have defined t and m, you can use the fft and fftshift functions to compute the discrete Fourier transform of m, which will give you an estimate of the discrete Fourier series. Then you can plot it in the frequency domain using the plot function.

HTH.

Rick