Jackson Labs PHASE STATION 53100A, Руководство пользователя

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PhaseStation 53100A User’s Manual V1.04 25-Apr-2022 67
axis labels don’t reflect the true amplitude of any coherent trace features. They
must be recognized as spurs, and their amplitudes indicated separately.
•
Trace → Suppress spurs in noise traces ( Ctrl-s ) attempts to remove known spurs
from phase noise and AM noise traces. As noted above, spurs that appear as
artifacts in noise traces are not rendered at their true amplitude levels due to the
use of FFT noise-bandwidth normalization. If you are concerned with spur
amplitudes in a given measurement, you should use
Trace → Suppress spurs in noise
traces ( Ctrl-s ) to erase each detected spur from the graph and Trace → Mark spurs in
noise traces ( Ctrl-m ) to replace them with vertical lines showing their true CW
amplitude levels relative to the carrier.
•
Trace → Smooth noise traces ( w ) always implies Trace → Suppress spurs in noise
traces ( Ctrl-s ) . For better visual quality, TimeLab will attempt to erase any known
spurs prior to smoothing the trace.
• Display → Numeric table ( Ctrl-n ) can be used to show or hide the spur chart for the
selected plot. Like the numeric charts and tables associated with other
measurement types, the spur chart appears to the right of the graph area. The
Ctrl-n command toggles table visibility for all measurement types, not just the
currently visible one.
Spur measurement options
The
Additional options
page in the PhaseStation 53100A’s acquisition dialog contains
four controls that influence how spurs are recognized and recorded.
• The choice of FFT Window implies a compromise between the accuracy at which a
given spur’s offset frequency and amplitude are reported. The default
Flat top
window excels at measuring spur amplitude levels, but the Hann window offers
better frequency resolution, and may improve the odds of detecting a given spur as
well.
• The Spur threshold field defaults to 6.0 dB. It defines the amplitude level, relative
to the average level of nearby FFT bins, below which a given bin’s amplitude will not
be considered indicative of a coherent spur. Lowering the threshold to 3 dB can
sometimes be helpful when tight mask-test requirements need to be met.
Figure 29: Window and spur controls