Fourier power spectrum calculations

[giker]

I have a programm that calculates Fourier Transform (FT) and Fourier Power Spectrum (FPS). I have data and I calculate Forier Trasform and Fourier Power Pectrum for this data. Everything looks right for FT but power spectrum looks very wrong. For example the larger value of amplitudes is equal 3.5E+2 on logarifmic scale, but larger value for FPS is equal 1.0E-12 on logarifmic scale. According my anderstanding power spectrum should be equal FT(k)^2. Window functions are not applyed in both cases.

Could you give me any idea how the power spectrum is calculated in LABVIEW?

Thank you.

[LocalDSP]

Pleeeeeaaaaaassssse attach your VI with saved input data so we can take a closer look at your actual situation.

[giker]

I use NI_AALPro.vlib:Auto Power Spectrum.vi from National Instruments to get power spectrum.

[LocalDSP]

... and that VI works as expected, so if you want us to help you we need DATA to understand what your problem is. Again the best would be to post your VI with both FFT and PS with input data saved by default that show the actual 'problem'.

[giker · Accepted solution]

I figured out why it works this way. Everything is correct. I didn't take into accaunt formula that LabView use for calculatinf power spectrum and bandwith noise. Thank you.