The Spectrum Application
R&S
®
FPC
117
User Manual 1178.4130.02 ─ 07
The RMS detector measures the spectral power over one pixel. In case of power
measurements, the RMS detector always shows the true power of a signal, regard-
less of the shape of the signal.
The RMS detector is best for measurements on digitally modulated signals
because it provides stable and true power readings. In combination with a high
sweep time, you can increase the display stability even more because the mea-
surement time for each pixel increases.
Noise measurements also provide stable results if you apply the RMS detector in
combination with a high sweep time.
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 the R&S
FPC shows is too low
because there are spectral components within the frequency range covered by the
pixel that do not originate from the signal you want to observe (e.g. noise).
To get the true power, the video bandwidth (VBW) should also be greater than the
resolution bandwidth (RBW). Otherwise, an averaging effect caused by video
bandlimiting comes into play before the RMS value is calculated.
●
"Sample "
The sample detector shows the last level that was measured in the frequency
range covered by a pixel.
The sample detector is useful for measurements in the time domain (span = 0 Hz)
as it provides the only way to represent the timing of the video signal correctly.
In the frequency domain, the sample detector is a good way to measure noise
power because noise usually has a uniform spectrum with a normal amplitude dis-
tribution.
Signals can get lost if you are using the sample detector for measurements with a
span that is greater than RBW*1183 (number of display points).
●
"Auto Detector"
The auto detector selects one of the detectors automatically, depending on the
selected trace mode.
For more information, see
Selecting the detector
1. Press the "Trace" key to open the trace menu.
2. Select the "Detector" menu item to open the detector menu.
The R&S
FPC opens a submenu to select the detector mode.
3. Select the detector you want to work with.
14.8.3
Memory Traces
Working with memory traces
You can save the image of both traces to the memory of the R&S
FPC and later
restore it, compare it to a live trace or apply trace mathematics. The memory trace has
a different shade of color to distinguish it from the live traces. In the spectrum applica-
tion, the R&S
FPC supports three memory traces.
Trace Configuration
