Appendix
R&S
®
Spectrum Rider FPH
467
User Manual 1321.1011.02 ─ 06.00
larly useful when sine signals are to be measured in the vicinity of the spectrum ana-
lyzer’s intrinsic noise. The sine signal produces a video signal that is a DC voltage.
At the IF, however, the noise is distributed over the whole bandwidth or, in the case of
the video signal, over half the bandwidth of the resolution filter. By selecting a narrow
video bandwidth relative to the resolution bandwidth, the noise can be suppressed,
while the sine signal to be measured (= DC) is not affected.
The figures below show a weak sine signal. In the first picture, it is measured with a
large video bandwidth and in the second with a narrow video bandwidth.
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 spec-
trum so that it can be represented as one pixel in the trace. The R&S Spectrum Rider
uses 711 pixels to form the trace, i.e. the whole measured spectrum has to be repre-
sented using just 711 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 mini-
mum 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
How a Spectrum Analyzer Works
