Spectrum analysis
R&S
®
RTP
408User Manual 1337.9952.02 ─ 12
● Enter a "Start frequency" and "Stop frequency" that define the spectrum.
● Tap the "Full Span" button to display the complete spectrum resulting from the
FFT analysis.
5. Define the resolution bandwidth for the FFT result.
The resolution bandwidth defines how precise the results are, i.e. how close
together the individual frequencies can be. Small values result in high precision, as
the distance between two distinguishable frequencies is small. Higher values
decrease the precision, but increase performance.
You can define the RBW manually, or couple it to other FFT settings. Do one of the
following:
● To couple the RBW to the span, enable the "Span/RBW coupling" option and
define the "Ratio". The smaller the ratio, the higher the RBW becomes to dis-
play the same frequency span.
● Enter the "Resolution BW" manually. The "Span/RBW coupling" option is auto-
matically disabled.
● To couple the RBW to the specified record length, in the " Gate" tab of the
"Advanced FFT" dialog box, select the "Record length controlled" option. This
option is only available if no gate is being used ("Use Gate" disabled).
6. Select the most suitable "Window type" for your source data. Window functions are
multiplied with the input values and thus can improve the FFT display. For details,
see "Window type" on page 413.
7. Optionally, select an arithmetic mode for the FFT segments. This mode defines
how the individual segment results are combined to a final spectrum waveform.
In the "Overlap" tab of the "Advanced FFT" dialog box, tap "Segment arithmetic"
and select the required mode from the list.
8. If you use an arithmetic mode, increase the "Overlap factor" for neighboring seg-
ments to increase the accuracy of the results.
To restrict the input values (gating)
By default, the FFT is calculated for the entire record length as defined for the data
acquisition. However, you can restrict the time range for which the FFT is calculated,
resulting in a restricted spectrum. Alternatively, the record length can be determined
automatically according to the selected RBW.
1. Open [FFT] > "FFT setup" > "Gate" tab.
2. Determine how the input length is configured by selecting one of the following
options:
● To ensure that the FFT is calculated for the full defined record length, select the
"Record length controlled" option. This option is only available if no gate is
being used ("Use Gate" disabled). The RBW is adapted so that the record
length can be acquired in the specified acquisition time. However, the RBW is
restricted, so that data acquisition may fail if the record length is too long for the
specified acquisition time.
FFT analysis
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