Is It A Spur, Or Isn't It; Understanding Instrument Spurs - Miles TimePod 5330A Operation And Service

Is it a spur, or isn't it?

Identifying genuine spurs while disregarding false ones can be a challenge. The 5330A's
DSP software may 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 near segment
boundaries. You can lower the
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
simply wait for the measurement to run long enough to reduce the trace variance
("grass").

Understanding instrument spurs

While TimeLab can sometimes overlook true spurs and report nonexistent ones, a third
type of measurement error may need to be considered as well: the presence of spurs
which originate within the instrument itself.
The spur-free dynamic range (SFDR) of the ADCs used in the 5330A is approximately 100
dB, which determines the corresponding specification limit of the instrument as a
whole. In principle, your noise plots may contain fictitious spurs as high as -100 dBc, but
the 5330A's typical performance is much better than this. Any spurs with amplitudes
above -120 dBc that remain visible as the measurement converges are almost certainly
"real" in the sense that they originate from the DUT, from the reference, or from
environmental RFI.
Regardless of the equipment used, spur-free observations of AM noise and phase noise
become challenging below -150 dBc. There are simply too many potential sources of
coherent artifacts to rule out in most cases. Still, spurs that originate within the 5330A
can sometimes be identified manually. An informal technique that may help determine
whether a given spur or spur cluster originates within the 5330A hardware itself is
illustrated in the side-by-side plots on the next page.
Spur Threshold for a given measurement, but the risk of
Spur Threshold, try changing FFT window types, or
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