How does the window selected on the spectral measurements express vi affect the output?

I'm using the spectral measurements express vi to find the power spectral density of a fairly broadband signal. I've already discovered a bug in the express vi; it doesn't divide the power spectrum by the equivalent noise bandwith for the window as it should. However, even after taking this into account by using the scaled time window vi to divide this factor out, the PSD is still changing with the window. How can I get the PSD to be constant with varying windows??

I would like you to prove the "bug" that you're describing by creating an example that shows the calculated and the expected results. By opening the code of the "Spectral Measurements" Express VI you can dig into the heart of the calculation, and there (in the "ma_FFT Power Spectrum and PS Density no State.vi") you will see that the Power Spectral Density indeed IS calculated by using the formula PSD = (Power Spectrum/(df*Noise Power BW of Window)). See the attached PSD.jpg that shows where the calculation happens.
The Power Spectral Density is supposed to be dependant of the chosen Window. Please read chapter 5 "Smoothing Windows" in the "La
bVIEW Analysis Consepts" manual.
Best regards,
Philip C.
National Instruments
- Philip Courtois, Thinkbot Solutions
Attachments:
PSD.JPG ‏139 KB

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I would like you to prove the "bug" that you're describing by creating an example that shows the calculated and the expected results. By opening the code of the "Spectral Measurements" Express VI you can dig into the heart of the calculation, and there (in the "ma_FFT Power Spectrum and PS Density no State.vi") you will see that the Power Spectral Density indeed IS calculated by using the formula PSD = (Power Spectrum/(df*Noise Power BW of Window)). See the attached PSD.jpg that shows where the calculation happens.
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Best regards,
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- Philip Courtois, Thinkbot Solutions
Attachments:
PSD.JPG ‏139 KB

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How does the window selected on the spectral measurements express vi affect the output?

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