Agilent Technologies E7405A User Manual
Chapter 1
39
Making Basic Measurements
Measuring Low Level Signals
NOTE
The video bandwidth must be set wider than the resolution bandwidth
when measuring impulse noise levels.
when measuring impulse noise levels.
Figure 1-31
Decreasing Video Bandwidth
Measuring Low Level Signals Example 4:
If a signal level is very close to the noise floor, video averaging is
another way to make the signal more visible.
another way to make the signal more visible.
NOTE
The time required to construct a full trace that is averaged to the
desired degree is approximately the same when using either the video
bandwidth or the video averaging technique. The video bandwidth
technique completes the averaging as a slow sweep is taken, whereas
the video averaging technique takes many sweeps to complete the
average. Characteristics of the signal being measured, such as drift and
duty cycle, determine which technique is appropriate.
desired degree is approximately the same when using either the video
bandwidth or the video averaging technique. The video bandwidth
technique completes the averaging as a slow sweep is taken, whereas
the video averaging technique takes many sweeps to complete the
average. Characteristics of the signal being measured, such as drift and
duty cycle, determine which technique is appropriate.
Video averaging is a digital process in which each trace point is
averaged with the previous trace-point average. Selecting
averaged with the previous trace-point average. Selecting
Average Type
,
Video Avg
and
Average (On)
changes the detection mode from peak to
sample. The result is a sudden drop in the displayed noise level. The
sample mode displays the instantaneous value of the signal at the end
of the time or frequency interval represented by each display point,
rather than the value of the peak during the interval. Sample mode is
not used to measure signal amplitudes accurately because it may not
find the true peak of the signal.
sample mode displays the instantaneous value of the signal at the end
of the time or frequency interval represented by each display point,
rather than the value of the peak during the interval. Sample mode is
not used to measure signal amplitudes accurately because it may not
find the true peak of the signal.
Video averaging clarifies low-level signals in wide bandwidths by
averaging the signal and the noise. As the analyzer takes sweeps, you
can watch video averaging smooth the trace.
averaging the signal and the noise. As the analyzer takes sweeps, you
can watch video averaging smooth the trace.