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R&S FSH
Spectrum Analyzer Mode
Configuring Spectrum Measurements
Operating Manual 1173.6275.12 - 30
103
► Press the "Manual RBW" softkey.
The R&S FSH opens an input field to define the resolution bandwidth.
► Enter the resolution bandwidth you need.
The R&S FSH uses the resolution bandwidth you have entered for the
measurement.
If the resolution bandwidth is no longer coupled to the span, the R&S FSH puts a
red dot at the "RBW" hardware setting (
).
► Press the "Auto RBW" softkey to again couple the resolution bandwidth to the
span.
Automatic adjustment of the sweep time
In its default mode, the R&S FSH automatically adjusts the sweep time as soon as you
change the resolution bandwidth. This is to make sure that the settling time required for
the selected resolution filter is properly taken into account.The maximum allowed
sweep time is 1000 s. For narrow resolution filters this value would be exceeded for
large spans. In order to avoid this, the R&S FSH adjusts the span automatically as
soon as the maximum sweep time is reached.
3.2.3.2 Setting the Video Bandwidth
The video bandwidth (VBW) basically smoothes the trace by reducing the noise and
therefore making power levels easier to see.
The noise reduction is a result of the video filter. This lowpass filter defines the video
bandwidth and filters the higher frequency parts of the voltage from the signal. Video
voltage is the (DC) voltage that results from the IF signal passing through the envelope
detector which removes the IF components and outputs the envelope only. This output
is also known as the video signal.
The figure below shows that process on an AM modulated signal in the time domain.
In case of an AM modulated signal, the envelope (or video) signal contains a DC
component that corresponds to the level of the carrier. The video signal also contains
an AC component whose frequency is the same as the AM frequency.