R&S FSH
How a Spectrum Analyzer Works
Functions of the Digital Modulation Analyzer
Operating Manual 1173.6275.12 - 30
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Limiting the video bandwidth smoothes the trace considerably. This makes it much
easier to determine the level of the measured signal.
The detector comes after the video filter. The detector combines the measured
spectrum so that it can be represented as one pixel in the trace. The R&S FSH uses
631 pixels to form the trace, i.e. the whole measured spectrum has to be represented
using just 631 pixels. Common types of spectrum analyzer detectors are the peak
detector (PEAK), the sample detector (SAMPLE) and the RMS detector (RMS). An
Auto Peak detector which simultaneously displays the maximum peak and the
minimum peak is usually also provided. The Fig. below explains how these detectors
work.
The figure above shows 30 measured values which are represented by a single pixel.
The peak detector determines and displays the maximum measured value. The Auto
Peak detector takes the maximum and minimum and displays them together. The two
values are joined by a vertical line segment. This gives a good indication of the level
variation over the measured values represented by a single pixel. The RMS detector is
used by the spectrum analyzer to determine the RMS value of the measured values. It
is therefore a measure of the spectral power represented by a pixel. The sample
detector takes an arbitrary measurement value and displays it (in the Fig. above, the
first). The other measured values are ignored.
