Fast Fourier Transform in MATLAB

Hello,

I'm facing a weird problem in MATLAB regarding fft and ifft functions. I have defined a Raised-Cosine filter in the frequency domain as shown.

With a roll-off factor r equal 1, the impulse response of the filter in the time domain should be Sinc with Null-to-Null Bandwidth equal to Ts as shown below

The above results are taken from MATLAB and they are completely correct according to Nyquist Criterion. But, now I'm running the code again and getting weird results in the impulse response output. The output now is Sinc with Amp 0.5 and Null-to-Null 2Ts. It seems that the signal is stretched out.

Any ideas about the root cause of such a problem?

Answer 1

[Matt J]

If you are getting different output from the same code, it can only mean that the input has changed.

[Taha Adel]

Nothing is changed neither the code nor the inputs to the program. Simply, the rect signal has bandwidth 1/2T in frequency domain should give SInc with Null-to-NUll Bandwidth equal to 1/T in time domain :(