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Using SMT Zoom Power Spectrum.vi with PXie-5162 Digitizer

Hello,

 

I'm recently implementing the Zoom FFT/Power Spectrum option in Spectral Measurements Toolkit with the high-speed digitizer PXIe-5162 vis niScope. I hope to obtain the high-frequency spectrum (near 1GHz) with low resolution bandwidth (RBW, <100). In the regular FFT/PSD vi, I have to take the whole spectrum with such small RBW, which takes a lot of space. Thus, I hope to use Zoom Power Spectrum to focus on a center frequency of 800MHz with a span of 100MHz, for instance.

 

I first use SMT Config niScope for Spectrum.vi to set the SMT Zoom settings. However, when I use a sampling rate of fs= 208MHz (just larger than 2*span frequency), the output "actual spectrum settings" shows that span is 100MHz but the center frequency is 52.08MHz instead of 800MHz.

 

I also notice that there is a property node of the niScope "Frequency Translation Enabled" under "Onboard Signal Processing -> DDC" that PXIe-5162 seems not supported. In this case, is it possible for me to use SMT Zoom Power Spectrum.vi to I get the "zoom-in" spectrum with a center frequency of 800MHz instead with a sampling rate of 208MHz? If yes, how should I do?

 

Also, I found it is difficult for me to understand the concept of "effective band specifications" in the "advanced settings". How much is the fh different from fs/2? Can it be automatically defined by a given span frequency and a given center frequency?

 

Thank you very much for your answers in advance.

 

 

 

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Hi mingweii,

The Zoom FFT is only meant to decrease the FFT computations, not decrease the initial data acquisition size as discussed in this article: https://www.embedded.com/design/other/4213370/Using-Zoom-FFT-for-spectral-analysis.  You could potentially use undersampling to lower the sampling rate depending on the bandwidth of the signal: https://www.eetimes.com/document.asp?doc_id=1275354#.

 

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