Jackson Labs PHASE STATION 53100A, User Manual

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PhaseStation 53100A User’s Manual V1.04 25-Apr-2022 49
Additionally, the 53100A driver can decimate the phase-difference data it acquires.
Readings are collected by sampling the internal phase-difference data stream at a rate
determined by the
Output Decimation field in the Additional options page of the
acquisition dialog. This feature is primarily for convenience. It can be used to reduce
the size of phase records generated by very long acquisitions, for example, or when high
data rates must be used in order to track drifting sources.
Decimation factors of 2:1 or greater also have the effect of satisfying the previous
τ
0
>= 1/(2 * ENBW) criterion. With the default Output Decimation value of 2:1 or any
higher ratio, phase-difference data that’s affected by lowpass attenuation will be kept
out of the measurement, even if
Trace → Clip xDEV traces by noise bandwidth ( Ctrl-b ) is
turned off.
Note that Trace → Clip xDEV traces by noise bandwidth ( Ctrl-b ) will have no effect on
plots rendered with data captured from counters and other instruments that don’t
report their measurement bandwidth. It should be left enabled in most cases.
Line-related spurs
The most conspicuous artifact in the ADEV plots above is the “ripple” in the blue and
magenta traces. This is caused by AC line interference, primarily a single 120-Hz spur:
Note that 1/120 Hz = 0.008s, which corresponds to the first (genuine) trough in the
ADEV traces above. Depending on how they’re introduced to the measurement, AC line
spurs commonly appear at either the fundamental power-line frequency or its second
harmonic. Users in the EU and other locales with 50 Hz power will see similar effects
near
τ =0.010 and 0.020s. In all of these cases, the device’s “true” ADEV is close to an
imaginary line drawn through all of the lowest points in the trace.
Getting rid of AC line spurs can be a challenge. Shielding at 50/60 Hz is usually
impractical; if the interference is magnetically coupled into the measurement, there is
probably no cure besides identifying the offending source(s) and moving sensitive
equipment and cables away.
Figure 14: AC line interference responsible for ripple in ADEV plots