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R&S FSH
Spectrum Analyzer Mode
Configuring Spectrum Measurements
Operating Manual 1309.6275.12 - 14
85
C
The resolution bandwidth affects the speed of the measurement. If you want to
display the true spectrum, the resolution filters have to settle at all frequencies that
are of interest. Narrow bandfilters have a longer settling time compared to wide
ones. Therefore the sweep time increases the smaller the resolution bandwidth
gets. The rule is, that if you reduce the bandwidth by a factor of 3, the sweep time
goes up by a factor of 9. If you reduce the bandwidth by a factor of 10, the sweep
time goes up by a factor of 100.
The R&S FSH has resolution bandwidths from 1 Hz to 3 MHz in a 1-3-10 sequence.
Additionally, the R&S FSH provides a 200 kHz resolution bandwidth that you have to
select and enter manually.
Setting the 200 kHz resolution bandwidth
The 200 kHz bandwidth is not coupled to the span, so it will not be selected if
automatic selection of the RBW is on.
In fact, you have to enter the 200 kHz resolution bandwidth with the number keys.
When using the rotary knob or the cursor keys, the 200 kHz bandwidth will be skipped.
In the R&S FSH's default state, the resolution bandwidth is coupled to the span, i.e. if
you change the span, the R&S FSH adjusts the resolution bandwidth. Therefore, you
do not have to set the resolution bandwidth manually in many cases, because the
R&S FSH automatically sets the resolution bandwidth if you change the span.
M
Press the BW key.
By default, the resolution bandwidth is coupled to the span.
M
Press the "Manual RBW" softkey.
The R&S FSH opens an input field to define the resolution bandwidth.
M
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 (
).
M
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.