Chapter 2 75
Front-Panel Key Reference
BW/Avg
NOTE If video averaging is selected, the measurement results are the average
of the signal level in the y-axis scale. If the power average (RMS) is
selected, all measured results are converted into power units before
averaging and filtering operations, and converted back to decibels for
displaying. The main point to remember is that there can be significant
differences between the average of the log of power and the log of the
average power.
There are actually four types of averaging processes within a spectrum
analyzer. All, except VBW filtering, are affected by this setting. They
are:
• Trace averaging (see
BW/Avg).
Averages signal amplitudes on a trace-to-trace basis. (Press Video or
Power (RMS) when
Avg Type (Man) is selected.)
• Average detector (see
Detector, Average).
Averages signal amplitudes during the time or frequency interval
represented by a particular measurement point.
• Noise Marker (see
Marker, Noise)
Averages signal amplitudes across measurement points to reduce
variations for noisy signals.
• VBW filtering.
Filtering the video is a form of averaging the video signal.
When trace average is on (
BW/Avg, Average (On), the Average Type is
shown on the left side of the display. When
Avg Type (Auto) is selected,
the analyzer chooses the type of averaging to be used as shown in
Figure 2-2 on page 71. When one of the average types is selected
manually, the analyzer uses that type without regard to the other
analyzer settings and sets
Avg Type to Man.
Key Access:
BW/Avg
Video Avg
Video averaging averages the data as appropriate for
the y-axis scale. When
Avg Type, Video Avg is selected,
VAvg appears on the left side of the analyzer display if
Average is On.
Key Access:
BW/Avg, Avg Type
Pwr Avg
Power averaging is performed by converting the trace
data from logarithmic to linear power units, and then
averaging the power trace data. When Avg Type, Pwr
Avg
is selected, PAvg appears on the left side of the
analyzer display if Average is On.
Key Access:
BW/Avg, Avg Type
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