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  How does vertical noise impact jitter measurements?

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Vertical noise can degrade a jitter measurement. It can be difficult or
impossible to determine with certainty whether trace thickness of a
signal´s edge is due to jitter or vertical noise.

It often helps to look at a flat portion of the waveform where the
amplitude is relatively constant and where the trace thickness is most
likely due to noise. Compare this trace thickness with that of the
signal edge to get an idea of how much of the jitter you measure is
actually caused by vertical noise.

You can use averaging to virtually eliminate vertical noise, although
this will also eliminate random jitter. To turn on averaging in the
54800-series Infiniium scopes, click *Setup | Acquisition*, select
*Enabled* under *Averaging*, and enter the desired *# of Averages*. To
quickly turn averaging on and off from the main waveform display window,
simply right-click on the display and select or deselect *Averaging*.

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