SVT FFT power spectrum initial value

[Beaton]

I am wondering why the initial value is so high when a i display the frequency content a my wave forms. The spectrum looks exactly like it should except at x = 0  the spectrum starts a a value much higher than should be seen.

[Ed W]

Hi Beaton,

Thank you for posting to the NI forums.  There aren’t any known bugs in the SVT FFT Spectrum (Mag-Phase).vi.  Could you try your spectrum analysis using the Power Spectrum express VI?  At the base level, these VIs are somewhat similar in functionality, so if you see similar results, it is probably because there really is a higher magnitude signal component at that frequency level. 

Also, how are you viewing the resultant spectral data – chart, graph, file, etc.?

Please post back with your results.  Thanks!

Ed W.

Applications Engineer

National Instruments

[johnsold]

If your waveform does not have an exact integer number of cycles, then it likely will have a DC component which would show up in the lowest frequency bin.

Lynn

[Beaton]

After more analysis it seems to be the dc offset in the waveform, thanks for your thoughts.