User`s guide

7-32
Operating Concepts
Analyzer Display Formats
Figure 7-17 Variations in Frequency Aperture
In determining the group delay aperture, there is a trade-off between resolution of fine
detail and the effects of noise. Noise can be reduced by increasing the aperture, but this
will tend to smooth out the fine detail. More detail will become visible as the aperture is
decreased, but the noise will also increase, possibly to the point of obscuring the detail. A
good practice is to use a smaller aperture to assure that small variations are not missed,
then increase the aperture to smooth the trace.
The default group delay aperture is the frequency span divided by the number of points
across the display. To set the aperture to a different value, turn on smoothing in the
average menu, and vary the smoothing aperture. The aperture can be varied up to 20% of
the span swept.
Group delay measurements can be made on linear frequency, log frequency, or list
frequency sweep types(not in CW or power sweep). Group delay aperture varies depending
on the frequency spacing and point density, therefore the aperture is not constant in log
and list frequency sweep modes. In list frequency mode, extra frequency points can be
defined to ensure the desired aperture.
To obtain a readout of aperture values at different points on the trace, turn on a marker.
Then press . Smoothing aperture becomes the active
function, and as the aperture is varied its value in Hz is displayed beneath the active entry
area.
Avg
SMOOTHING APERTURE