PhaseStation 53100A User’s Manual V1.04 25-Apr-2022
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Spur min offset
is normally 0.0 Hz. It can be set prior to acquisition by entering an
offset frequency below which spurs will not be logged for processing. The minimum
spur offset can also be adjusted in the
Edit→Trace properties
dialog at any time
after acquisition is complete. This feature can be especially helpful when large
‘bumps’ in the flicker noise region are incorrectly classified by TimeLab as either real
spurs or instrument spurs. 1 Hz is a reasonable value to start with in these cases.
•
When the
Attenuate instrument spurs
option is checked, the 53100A driver
software will use the phase component of a given spur’s peak FFT bin to attempt to
classify it as an instrument artifact or a genuine result of the measurement.
Instrument spur discrimination is enabled by default and discussed in detail below.
Additionally, note that both spur-identification performance and acquisition time will be
affected if the
Edit segment table
button is used to change the FFT kernel sizes used in
the individual noise-trace segments. While lower-resolution segment definitions can
result in faster measurements, they can also cause large elevated regions to appear
where “forests” of discrete spurs are too closely-spaced to resolve.
Is it a spur, or isn’t it?
Identifying genuine spurs while disregarding false ones is a difficult problem in the
general case, and no spur-discrimination algorithm is infallible. The 53100A’s DSP
software may occasionally fail to detect spurs when they occur in clusters near the FFT
segment’s resolution limits, in steeply-sloped areas of the noise trace, or in other parts
of the trace where an obvious baseline is not clearly discernible.
You can lower the
Spur Threshold
for a given measurement, but the risk of
misclassifying random noise spikes as coherent spurs will become greater. When you
see random spurs appear and disappear from the spur chart over the course of a
measurement, you can increase the
Spur Threshold
, try changing FFT window types, or
simply wait for the measurement to run long enough to reduce the trace variance
(“grass”).
As mentioned above, you can also tell TimeLab to ignore spurs close to the carrier with
the
Min Spur Offset
field in the
Edit
→
Trace Properties
dialog. This option can also be
specified at acquisition time in the 53100A acquisition dialog’s
Additional options
page.
Summary of Contents for PHASE STATION 53100A
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