What does the 'Excess Span (Hz)' mean in RBW filter?

Updated Feb 18, 2024

Reported In

Software

  • RFmx
  • RFmx SpecAn

Issue Details

I'm reading the RFmx SpecAn manual:

https://www.ni.com/docs/en-US/bundle/rfmx-specan/page/digital-emulation-rbw-filters.html

I understand that the selection of the RBW filter will take affect to emulate the behavior what a swept-spectrum does.

rbw_filter.png
However, I don't know the meaning of the 'Excess Span (Hz)' column in the table below, what does the RBW and 5 x RBW mean here?

Solution

Excess span is how much extra spectrum the measurement needs in addition the user configured span/bandwidth for the measurement. RFmx will take care of this automatically when it configures and acquires data from the hardware.
Let's say the user configures the SpecAn Spectrum measurement with a Span of 10 MHz and an RBW of 10kHz, when using Gaussian RBW filter, the measurement needs 10 MHz + 5x10kHz of spectrum for the measurement to work correctly.

Related Links

Digital Emulation of Analog RBW Filters - NI

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