Rohde & Schwarz FPC1000 User Manual page 110

FPC1000
The auto peak detector loses no information. If a signal's power level fluctuates (for
example in case of noise), the width of the trace depends on the magnitude of the
signal fluctuation.
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"Max Peak"
The max peak detector displays only the highest level that was measured in the
frequency range covered by a pixel.
The max peak detector is useful for measurements on pulses or FM signals, for
example.
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"Min Peak"
The min peak detector displays only the lowest level that was measured in the fre-
quency range covered by a pixel.
The min peak detector displays sine signals with the correct level and suppresses
noise. Therefore it is useful to find sine signals in the vicinity of noise.
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"RMS"
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 FPC1000 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.
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"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).
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"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.
User Manual 1178.4130.02 ─ 02
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Chapter 9.8.1, "Trace Mode",
The Spectrum Application
Trace Configuration
on page 93.
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