Jackson Labs PHASE STATION 53100A, User Manual

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PhaseStation 53100A User’s Manual V1.04 25-Apr-2022 85
Flatten selected noise region ( Ctrl-F8 )
This feature allows you to remove known spurs and other artifacts from a phase noise
or AM noise plot. It can be helpful in cases where the automated spur identification
process falls short, such as when a PN or AM noise mask test is failing due to a low-level
instrument artifact or a known external interference source.
Figure 33 below shows a phase noise mask test that has failed with a -0.4 dB margin due
to an unrecognized spur at an offset near 25 Hz. This spur is too close to the
surrounding noise to be flagged and suppressed by TimeLab, either as a real spur or an
instrument artifact, but it’s strong enough to exceed the limit line and cause a test
failure. Pressing Ctrl-F3 (
Trace→Show imaginary part of cross spectrum
) reveals that
the spur is a low-level instrument artifact. It is not only visible in the imaginary part of
the cross spectrum, but its amplitude is actually stronger there. This spur is a good
candidate for manual removal.
Figure 34 at right illustrates the workflow: after switching back to the
real cross spectrum with Ctrl-F3 and pressing F2 to hide the noise-floor
estimate for better visibility (
Trace→Show estimated instrument
noise ), simply drag a box to zoom in on a portion of the plot
containing the base of the spur in question. Then, hold down the Shift
key and left-drag to create a flat line segment that spans the area to
be flattened. Choose endpoints that will blend effectively with the
areas of the trace to be retained.
Once the segment has been drawn in the desired location, use Ctrl-F8
(
Edit→Flatten selected noise region ) to create a trace segment
between the specified endpoints. Right-click anywhere in the window
to zoom back out, and observe that the mask test now passes, as
shown in Figure 35 below.
Figure 33
Figure 34