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How to interpret RBW and VBW in FFT spectrum analyzer

Question asked by apwagner on Jul 11, 2014
Latest reply on Apr 5, 2017 by Macree

I'm a using a N9000A CXA spectrum analyzer, which has the capability of producing spectral measurements from an FFT rather than only the heterodyne technique. My question is how to interpret the RBW and VBW in terms of the spectral resolution (frequency resolution) and sweep time (integration time) for an FFT spectral measurement? I understand what VBW means for a heterodyne measurement but am uncertain what it actually does in the context of an FFT. Does it just amount to taking some number of spectra, each for an integration time of 1/RBW, and averaging? If someone could point me to a good technical note describing what the spectrum analyzer is actually doing "under the hood" when making an FFT spectrum I would greatly appreciate it. Thanks very much for your time and help.