Common Analysis and Display Functions
R&S
®
FSPN
154
User Manual 1179.4363.02 ─ 01
hold, min hold or write hold. For the smoothing process, a median filter is applied on
the logarithmic data.
You can turn trace smoothing on and off for all traces individually and compare, for
example, the raw and the smooth trace.
7.3.1.3
Spurs and Spur Removal
Most phase noise results contain unwanted spurs. Spurs are peak levels at one or
more offset frequencies and are caused mostly by interfering signals. For some appli-
cations, you might want to identify the location of spurs. For other applications, spurs
do not matter in evaluating the results and you might want to remove them from the
trace to get a "smooth" phase noise trace.
Spur display
Usually, spurs are visible on the trace as a peak. In addition, the R&S
FSPN draws a
straight, vertical line to represent the position of a spur visually. The length of these
lines indicates the level of the spur in dBc and refers to the scale on the right side of
the phase noise diagram.
The lines indicating a spur are not part of the trace data. When you export the trace, for
example, the spur data is not exported.
Spur suppression
The application allows you to (visually) remove spurs from the trace. Spur removal is
based on an algorithm that detects and completely removes the spurs from the trace
and fills the gaps with data that has been determined mathematically.
The spur removal functionality separates the actual spur power from the underlying
phase noise and displays the latter in a two-stage process. The first stage of spur
detection is based on an eigenvalue decomposition during the signal processing.
Spur threshold
During the second stage, the application uses statistical methods to remove a spur. A
spur is detected, if the level of the signal is above a certain threshold. The spur thresh-
old is relative to an imaginary median trace that the application calculates.
If parts of the signal are identified as spurs, the application removes all signal parts
above that level and substitutes them with the median trace.
Trace Configuration
