Chapter 10: Resolution And Video Bandwidth; Resolution Bandwidth Filter (Rbw); Video Bandwidth Filter (Vbw) - Deviser S7200 User Manual

Chapter 10: Resolution and Video Bandwidth

10-1

Resolution Bandwidth filter (RBW)

The frequency resolution is the ability to clearly distinguish 2 input sine wave signal responses of a spectrum
analyzer. The ability of a spectrum analyzer to distinguish signals is generally described within 3dB of the
available bandwidth IF filter.
For analog intermediate frequency:
The bandwidth of the smallest intermediate frequency filter generally determines the resolution bandwidth
capability of an instrument.
Switching from one filter to another offers a different resolution of the measurement. Wide resolution
bandwidth filters require less time to scan, are more stable when the sweep time is shorter (faster), require
less time for the signal to reach full amplitude within the filter shape as it is scanning through. However, they
offer less resolution, dynamic range and lower S/N range. Narrower bandwidth filters requires more time, or
slower sweep time setting to allow the full amplitude of the signal to be measured, to be reached within the
filter as it is scanning, but it does offer a much higher resolution, better dynamic range and better S/N.
The S7200 offers automatic or manual RBW selection depending on frequency/span/sweep time selection
and/or what the user is looking for. The S7200 uses digital IF and leverages DSP (Digital Signal Processing)
techniques of implementation, so the digital filters won't drift as analog filters would in older spectrum
analyzers. Digital IF technology provides VERY good measurement stability with a much wider selection of
Frequency/Span/Sweep times, and still provide a very stable and accurate measurement.
10-2

Video Bandwidth filter (VBW)

In order to reduce the influence of noise variations in the display of signal amplitude, Spectrum Analyzers
typically smooth or average the trace display. The selectable video bandwidth filter in a spectrum analyzer
is used for that purpose.
It is a low-pass video filter, which determines the bandwidth of the video signal located behind the
envelope detector. The value of this video filter is typically lower than the RBW selected. The intended
purpose is to average or smooth the displayed signal.
Part III: Background and Concepts
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