Chapter 6 6-15
Front-Panel Key Reference
BW/Avg
Average Type
Video Power
Average Type (Video) initiates a digital averaging routine that averages
on a point-by-point basis over a number of successive sweeps. The effect
is to minimize the impact of transients on the displayed signals and
noise. The number of sweeps (N) to average is the number that is set by
this function. This function automatically selects the
Sample detector,
but does not affect the sweep time, bandwidth, or other analog
characteristics of the analyzer. Annotation on the left side of the display
indicates the current number of sweeps averaged. The default number
of sweeps is 100. Increasing the number of sweeps will further averages
the trace. To turn off the averaging function, press
Average (Off). The
number of sweeps can only be entered using the numeric keypad.
In single sweep mode (Sweep, Sweep (Single)), N sweeps are taken. After
each sweep, the new value of each display point is averaged in with the
previously averaged data using the following formula:
Where:
In continuous sweep mode (
Sweep, Sweep (Cont)), the same sequence is
followed until M=N. At that point, the sweeps continue rather than
stopping. For each new sweep, the measured value of the current sweep
divided by N is added to (N-1)/N times the prior average, creating a
weighted rolling average.
If any measurement parameter, such as
Center Freq, Span, Ref Level, or
N, is changed while
Video Average is On, the video average counter is
reset to 0, i.e. M=0, and the trace average resets. If the analyzer is in
single sweep mode, a new set of sweeps is taken only after
Sweep
(Single) is pressed again.
When
Average Type (Video) is selected, VAvg appears on the left side of
the analyzer display if
Average is On.
When
Average Type (Power) is selected, power averaging is performed by
converting the trace data from dB to power units, and then averaging
the power trace data. When
Average Type (Power) is selected, PAvg
appears on the left side of the analyzer display if
Average is On. Power
averaging is slower than video averaging due to the additional
computations necessary.
A
avg
M1–
M
--------------
A
prior avg
1
M
-----
A
m
+=
A
avg
new average value=
A
prior avg
average from prior sweep=
A
m
measured value on current sweep=
M number of current sweep=
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