Trace Settings R&S FSH3
Detector
The detector processes a spectrum analyzer’s video voltage before it is displayed. The detector is pixel-
oriented, i.e. it determines how the level at each pixel will be displayed. The R&S FSH3 always
measures the whole spectrum. However, the trace only has 301 pixels in the x direction for displaying
results. If a large span is selected, all the spectrum information must somehow be represented using
only 301 points. Each pixel represents a frequency range equal to span/301. Four different detectors
are available:
• AUTO PEAK When the Auto Peak detector is selected, the R&S FSH3 displays
the maximum and minimum level at each pixel for the frequency
range in question. This means that when Auto Peak detection is
selected no signals are lost. If the signal level fluctuates, as is the
case with noise, the width of the trace is a measure of signal
fluctuation. Auto-peak detection is the default setting.
• MAX PEAK Unlike the Auto Peak detector, the Max Peak detector only finds
the maximum value within the frequency range associated with
one trace pixel. Its use is recommended for measurements on
pulse-like signals or FM signals.
• MIN PEAK The Min Peak detector yields the minimum value of the spectrum
within a pixel of the trace. Sine signals are displayed with correct
level but noise-like signals are suppressed. The Min Peak detector
can be used to highlight sine signals in the noise spectrum.
• SAMPLE The Sample detector does not “summarize” any aspect of the
spectrum which is available in its complete form in the R&S FSH3,
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 FSH3 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 FSH3 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).
1145.5973.12 4.20 E-6
To Next Page
Loading...
