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89600 VSA software:question about VBW and averaging.

Question asked by Macree on Mar 24, 2017

Hi everyone!I have a question about VBW function in the 89600 VSA software.It use 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 help file says:"The 89600 software power spectrum measurement emulates a traditional VBW filter by averaging blocks of FFT results to achieve a similar variance reduction for the same VBW value that a traditional swept analyzer would have."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?Thanks.