PhaseStation 53100A User’s Manual V1.04 25-Apr-2022
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limited to the real axis… but unlike random noise, the real amplitude of some of these
spurs may not average to zero over time. These spurs appear on the graph as
instrument artifacts.
Switching to the
Trace
→
Show imaginary part of cross spectrum display (
Ctrl-F3
)
view
at right reveals the noise and spurs that correspond to the imaginary part of the cross-
spectrum average, specifically the absolute value of the Q-component at each bin.
Ordinarily this data is used only to create the shaded area used by the
Trace
→
Show
estimated instrument noise (
F2
)
feature, after undergoing heavy averaging. But
Ctrl-F3
lets us view the imaginary part of the cross spectrum at full resolution. It’s readily
apparent that the spur near 50 kHz has
almost the same amplitude in the imaginary
cross spectrum as it does in the real measurement.
This is a strong indicator that the spur is an instrument artifact. When
Attenuate
instrument spurs
is selected in the 53100A acquisition dialog, spurs with high imaginary
amplitude components are removed from the plot regardless of the state of all other
smoothing and spur-suppression options.
There are other spurs in the imaginary cross spectrum that correspond to similar spurs
in the real plot, but most appear to be AC line harmonics that both the 53100A and the
sources under test are exposed to, and their amplitudes are substantially different.
Although the
Ctrl-F3
technique isn’t foolproof, it can offer some valuable insight when
you need to account for unanticipated low-level spurs.
Manual spur removal
As noted above, instrument spurs can be overlooked by the software for several
reasons. They may be below the spur-detection amplitude or Fourier offset thresholds
specified in the instrument’s acquisition options dialog (where applicable), or they may
be too low in amplitude to be recognized as a spur at all. At the same time, a spur that
is
recognized may not be correctly flagged and removed as an instrument spur if its
phase lies close to the real axis.
These cases often resolve themselves if the measurement is allowed to run long enough
for the SNR to improve. If not, the
Edit→Flatten selected noise region (
Ctrl-F8
)
command can help in particularly stubborn cases – for instance, when an unrecognized
artifact must be removed in order to pass a mask test, or when a trace with excessive
noise variance needs to be cleaned up for publication. Refer to the
Edit→Flatten
selected noise region
command description for more information.
Summary of Contents for PHASE STATION 53100A
Page 1: ...TM 53100A Phase Noise Test Set User s Manual Revision 1 04 April 25 2022...
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