Spectrum Analyzer Mode
R&S
®
Cable Rider ZPH
222
User Manual 1321.0950.02 ─ 07
The resolution bandwidth (RBW) has several effects on measurements.
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To be able to display two or more signals whose frequencies are close together
separately, you need a (resolution) filter whose bandwidth is small enough. The fre-
quency difference between two sinusoidal carriers cannot be less than the selected
resolution bandwidth if the carriers are to be resolved, for example.
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The bandwidth of the resolution filter also affects the noise that is displayed by the
R&S Cable Rider ZPH. The smaller the bandwidth, the less noisy the results are.
The rule is, that if you increase or decrease the bandwidth by a factor of 3, the
noise goes down or up by 5 dB. If you change the bandwidth by a factor of 10, the
displayed noise changes by 10 dB.
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The resolution bandwidth affects the speed of the measurement. If you want to dis-
play the true spectrum, the resolution filters have to settle at all frequencies that
are of interest. Narrow band filters 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 Cable Rider ZPH has resolution bandwidths from 1 Hz to 3 MHz in a 1-3-10
sequence.
In the R&S Cable Rider ZPH's default state, the resolution bandwidth is coupled to the
span, i.e. if you change the span, the R&S Cable Rider ZPH adjusts the resolution
bandwidth. Therefore, you do not have to set the resolution bandwidth manually in
many cases, because the R&S Cable Rider ZPH automatically sets the resolution
bandwidth if you change the span.
1. Press the [DTF/BW] key.
By default, the resolution bandwidth is coupled to the span.
2. Select the "Manual RBW" softkey.
The R&S Cable Rider ZPH opens an input field to define the resolution bandwidth.
3. Enter the resolution bandwidth you need.
The R&S Cable Rider ZPH uses the resolution bandwidth you have entered for the
measurement.
If the resolution bandwidth is no longer coupled to the span, the R&S Cable Rider
ZPH puts a blue dot at the "RBW" displays on the "Parameter View".
4. Select the "Auto RBW" softkey to again couple the resolution bandwidth to the
span.
Configuring Spectrum Measurements
