Hi everyone.I have a question about VBW function in the pna-x spectrum analyzer option.It uses FFT method to transfer signal from time domain to frequency domain,so it can't use low-pass filter as VBW filter.To solve the problem,trace average is used instead.The question is ,what's the mathematical relationship between RBW/VBW ratio and average count?Is there a function I can use to calculate average number according to RBW/VBW ratio?And is the averaging count related to RBW shape and averaging type?

http://www.ni.com/tutorial/13869/en/ This is an file I read about calculating averaging count,but I'm not sure it's right or not.Dose PNA-X use the same method?Thanks.

PNA SA mode uses the formula: intval = floor( (0.8 + 0.38 * rbw / vbw) + 0.5

I think this is the same as used in PXA when it uses the FFT mode, and emulates VBW values.

Of course, the number of FFT averages can only be an integer.

Averaging mode does not affect the count nor does the RBW shape. Changing averaging mode, changes the computation for trace average, VBW average, and averaging detector (all use the same mode).