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The advantage of video averaging over narrowing the video filter is the ability of the user to see changes made to
the amplitude or frequency scaling of the display while smoothing the noise response. For example, when a 100
Hz video bandwidth is used with a 200 kHz frequency span, the sweeptime is 2 sec. Almost a full sweeptime
duration would have to pass before any center frequency change effect on the trace could be seen. If video
averaging is used instead of the narrow video bandwidth, any change to center frequency will be seen immedi-
ately, even though full averaging will take roughly 6 sec. (Any change to control settings such as CENTER
FREQUENCY FREQUENCY SPAN, etc., will cause the video averaging process to be restarted.)
Example
To display very low-level signal responses, very narrow resolution and video bandwidths are required. The accom-
panying increase in sweep time can make measurements cumbersome. Video averaging allows the display of low-
level signals without the long sweep time.
Viewing a low-level signal with a video bandwidth of 1
Hz requires a 150-second sweep.
Disable the narrow video filter by pressing the (wr(ll
key that is above the m key.
Start video averaging by pressing (,.,,, h
Now the low-level signals begin
Changes to the frequency range or amplitude scale
will restart the sampling to show the signals quickly,
without having to wait 150 seconds. In fact, the video
averaging shown took 42 x 300 msec = 12.6 sec.
Video Averaging Algorithm
The averaging of each amplitude point depends upon the number of samples already taken and last average
amplitude.
102 Manual Operation
show quickly.
to
n-l
1
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