Specifications

30 Chapter 3
Measuring a Low−Level Signal
Trace Averaging
Measuring a Low
−
Level Signal
Trace Averaging
Averaging is a digital process in which each trace point is averaged with
the previous average for the same trace point. Selecting averaging,
when the analyzer is autocoupled, changes the detection mode (from
peak in ESA and normal in PSA) to sample, smoothing the displayed
noise level. ESA sample mode displays the instantaneous value of the
signal at the end of the time or frequency interval represented by each
display point (for PSA it is the center of the time or frequency interval),
rather than the value of the peak during the interval. Sample mode
may not measure a signal’s amplitude as accurately as normal mode,
because it may not find the true peak.
NOTE This is a trace processing function and is not the same as using the
average detector (as described on page 29).
Step 1. Refer to the first procedure “Reducing Input Attenuation” on page 26 of
this chapter and follow steps 1, 2 and 3.
Step 2. Turn video averaging on:
Press
BW/Avg, Average (On).
As the averaging routine smooths the trace, low level signals become
more visible. Average 100 appears in the active function block.
Step 3. With average as the active function, set the number of averages to 25:
Press
25, Enter.
Annotation on the left side of the graticule shows the type of averaging
(the annotation for ESA is VAvg and is LgAv for PSA), and the number
of traces averaged.
Changing most active functions restarts the averaging, as does toggling
the
Average key. Once the set number of sweeps completes, the analyzer
continues to provide a running average based on this set number.
NOTE If you want the measurement to stop after the set number of sweeps,
use single sweep: Press
Sweep, Sweep (to select Single), or press Single
and then toggle the Average key.