HP 54645A User's And Service Manual page 98

MegaZoom Concepts
Display Modes
Average Mode
Averaging is a way to pull the signal out of the noise. Averaging works better
than either a bandwidth limit or a brightness control. The averages you can
select include "Smoothing", 4, 8, 16, 32, 64, 128, and 256.
Smoothing is an oversampling technique, and operates as described in
the "Display Modes" section in this chapter. Smoothing is the opposite of
peak detect: as the sweep speed slows, the samples are averaged
together to form a single sample, effectively suppressing noise.
Smoothing also allows averaging on a single trigger.
When smoothing is used, the slower the sweep speed, the greater the number
of samples that are averaged together for each display point. The slower the
sweep speed, the smoother the trace is on the scope display.
Recall that in normal display mode, at sweep speeds faster than 2 s/div, you
see all the 5-ns samples, and thus peak detect has no effect. The same is true
of smoothing. It will have no effect at sweep speeds of 2 s/div and faster.
Note that the Av status indicator is not highlighted.
Averaging: 4, 8, 16, 32, 64, 128, 256 lets you average multiple
triggers together to reduce even more noise than can be achieved on the
scope display. The number indicates the number of triggers to be
averaged together. The higher the number, the more noise reduction that
will be accomplished. This will average a number of "smoothed" triggers
together.
The average displayed on the scope screen is a "display average." This means
that all the data used to obtain the average display is not retained by the
scope. Thus, if you want to pan and zoom the averaged waveform, only the
last smoothed data is displayed. See "Recovering the Waveform on the
Screen" in this chapter for more information.
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