FFT Spectrum (Mag-Phase).vi (and associated FFT family of VIs)

[DonRoth]

Hi – I was wondering about how delta f is calculated using the FFT family of VIs.

Generally, Delta f is calculated from:

delta f = (sampling rate/N)

For data I have gotten, N = 2048 points, sampling rate = 6.4E+12 Hz, and thus delta f = 3.125E+09 Hz.

However, delta f output from FFT Spectrum (Mag-Phase).vi is ~ 10x this at 31.25E+09.

I can improve the frequency resolution thru interpolation or curve fitting but I was surprised at this result.  Is this larger delta f used to improve speed of calculating the FFT magnitude and phase spectra?

Sincerely,

Don

[DonRoth]

....The light bulb went on (for some reason while watching the Colbert Report!).  I had applied a gate to subset the entire waveform so the number of points was not the that for the entire waveform, it was just the number in the gate. 

It does appear then that the FFT familiy of VIs delta f = (sampling rate/N) = 1/([delta t]*N) as when I removed the gate, the delta f was reduced by an order of magnitude.

Thanks for looking.

Don