Integer number of waveform for FFT

[thoalfukar]

Dear All,

I have waveform from scop and I am trying to do FFT  for that wave in order to see the phase and magnitude for each harmonic. 

Now the FFT is not working well because I know what the faundamental should be for example I know the faundamental should be -14.56 dbm while the FFT in my code show me -21 dbm. 

I know one of the spectral leakage causes this problem and to solve this problem I should inject integer number of waves to the FFT. 

Could any of you help me with this problem. 

knowing that I did the FFT for the same waveform in Matlab and I got result better than in labview but still not right (I got for the faundamental  -17.9 dbm).

Thank you

best regards

Thoalfukar 

[nanocyte]

Yes, try that. Clip the waveform at nearby zero crossings to get an integer number of waveforms. Also, in general, you'll want as many samples as possible at the highest sampling rate.