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RBW vs VBW

This page on RBW vs VBW covers difference between RBW(Resolution Bandwidth) and VBW(Video Bandwidth) terms used in spectrum analyzer.

Both RBW and VBW are terms used in spectrum analyzer for measurement purpose.

RBW-Resolution Bandwidth

RBW stands for Resolution Bandwidth; it is used to view distinctly two very closely spaced signals in frequency domain. It is mainly used for phase noise measurement purpose.

Resolution bandwidth (RBW) filters are bandpass filters located in the spectrum analyser's final IF stages. They determine how well closely spaced signals can be separated. The narrower the RBW filter the more clearly two close signals can be seen as separate signals. The RBW filters also determine the analyser response to pulse signals and to noise. The resolution bandwidth control selects which RBW filter is used.


RBW vs VBW

The shape of a spectrum displayed on the analyser screen is a combination of the shape of the RBW filter and the shape of the true signal spectrum. The figure-1 depicts filters used for RBW and VBW tuning.

RBW filters are defined by their bandwidths and shape factors. Bandwidth is specified in Hz either at 3 dB or 6 dB down from the filter peak. The shape factor, which indicates the steepness of the filter, is the ratio of the RBW filter bandwidth 60 dB down from the peak to its normal (3 dB or 6 dB) bandwidth. The shape factor is important in determining the minimum separation between two signals which have equal amplitudes to be resolved.

VBW-Video Bandwidth

VBW stands for Video Bandwidth; helps improve resolution of very weak signals in the presence of the noise signal. It is post detection filter bandwidth which just smoothes out signal of interest. It is used to reduce noise on trace, It doesn't reduce noise floor.

VBW is associated with video filter. The position of video filter is after envelope detector and just before displaying the signal on the screen display.

Useful Links

RF measurements tutorial,READ MORE
Phase noise vs Jitter, READ MORE

RF and Wireless Terminologies


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