Jackson Labs PHASE STATION 53100A, User Manual

Page: 72 / 225

PhaseStation 53100A User’s Manual V1.04 25-Apr-2022 72
Hints for noise measurements
•
The 53100A can render an estimate of its own noise floor in AM/PM noise plots if
you enable
Trace → Show estimated instrument noise ( F2 ) . See page 100 for more
information.
•
For AM and phase noise, a good indication that the noise trace has converged on its
final level is the variance of the trace, or its overall fuzziness/thickness. If you
measure a conventional signal generator or noisy oscillator, you’ll notice that the
trace stops falling relatively quickly after the measurement begins, and then
becomes smoother over time. This 'smoothing' effect is an important cue that tells
you how trustworthy your noise measurement is. With quiet sources, close-in
segments can take an especially long time to converge at a final, smoothed level,
since they are updated much less often.
• Crosstalk and AC power-line interference can create discrete spurs on phase noise
and AM noise graphs, just as they can degrade ADEV and other statistical plots. See
page 49 for a discussion of causes and cures.
•
TimeLab has a graph-smoothing feature ( Trace → Smooth noise traces ( ctrl-w ) ) but
it’s not always needed with a cross-correlating analyzer such as a PhaseStation,
TimePod, or Microsemi 5120A/5125A. The best way to obtain a smoother trace
with these instruments is often to let your measurement run longer. Low-noise
plots can benefit from
Trace → Smooth noise traces (
ctrl-w
)
, but many
measurements don’t need additional smoothing at all.
• Another tip for smoother phase noise and AM noise traces, suitable for 53100A
users with faster PCs: enable the
Overlapped acquisition option in the Additional
options page of the acquisition dialog. Overlapped acquisition provides much more
efficient utilization of incoming data by the FFT routines, but requires significantly
more CPU time. (Note that FFT overlapping is different from the algorithm used in
overlapped Allan deviation and other stability statistics. Overlapped statistical
calculations are always performed, while overlapped FFT processing in noise data
acquisitions is turned off by default.)
•
When overlaying several measurements on the screen, it can be helpful to run with
spurs removed from the trace (
Trace → Suppress spurs ( Ctrl-s ) enabled) and
unmarked on the graph ( Trace → Mark spurs ( Ctrl-m ) disabled). Trace → Smooth
noise traces ( ctrl-w ) will automatically suppress spurs.