R&S FSH
Trace Settings
1145.5973.12 4.21
E-14
•
SAMPLE
The Sample detector does not “summarize” any aspect of the
spectrum which is available in its complete form in the R&S FSH,
but instead shows only one arbitrary measurement point within a
pixel. The Sample detector should always be used for
measurements with span = 0 Hz, as this is the only way of
correctly representing the timing of the video signal. The Sample
detector can also be used to measure noise power as noise
usually has a uniform spectrum with a normal amplitude
distribution. If the Sample detector is used for signal spectrum
measurements with a span that is greater than (resolution
bandwidth x 301), signals may be lost.
•
RMS
The RMS detector measures spectral power over a pixel. No
matter what the signal shape, power measurements with the RMS
detector always give the true power. RMS detection is
recommended for power measurements on digitally modulated
signals in particular. This is because the RMS detector is the only
R&S FSH detector that can give stable, true power readings.
Display stability can easily be obtained by increasing the sweep
time, as the measurement time for the power/pixel increases the
greater the sweep time. If you are making noise measurements,
for example, the trace will be highly stable if a long sweep time is
selected.
However, the bandwidth occupied by the signal to be measured
should at least equal the frequency covered by a trace pixel or the
selected resolution bandwidth (whichever is larger). Otherwise, the
power shown by the R&S FSH is too low because there are
spectral components within the frequency range covered by the
pixel which do not come from the signal under measurement (e.g.
noise).
To obtain the true power, the video bandwidth (VBW) too should
be selected to be greater than the resolution bandwidth (RBW).
Otherwise, an averaging effect caused by video bandlimiting
comes into play before the RMS value is calculated.
Both automatic operation and manual operation are available for setting the detector. In automatic
operation, the R&S FSH selects the detector that is suitable for the trace mode that is set. In manual
operation, the selected detector is always maintained regardless of the trace mode.
Setting of the detector in automatic operation:
Trace mode
Detector
Clear/Write Auto
Peak
Average Sample
Max Hold
Max Peak
Min Hold
Min Peak
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