User manual
Mathematics
R&S
®
RTO
196User Manual 1316.0827.02 ─ 06
6.3.2 Configuring FFT Waveforms
During FFT analysis, a signal in the time domain is converted to a spectrum of frequen-
cies. A basic FFT waveform can be displayed very quickly. By defining additional FFT
parameters, the waveform can be configured in more detail.
As a result, either the magnitude or the phase of the determined frequencies can be
displayed, or more complex FFT functions. Analysis can be restricted to an extract of the
original time base, and the results display can be restricted to a specified frequency
range.
To display a basic FFT waveform
1. Tap the "FFT" icon on the toolbar, then tap the waveform for which the FFT is to be
performed.
FFT
The first available math waveform is configured to use the selected waveform as a
source and the "Mag(FFT(x))" operator and is enabled. The FFT waveform is dis-
played in a new diagram.
2. Alternatively, press the MATH key to open the "Math" dialog box.
3. In the "Setup" tab, in the "Optimized" expression editor, select the input signal as
"Source 1".
4. Select "Mag(FFT(x))" as the "Operator".
5. Select the "Enable math signal" icon.
6.
If required, edit the FFT waveform parameters as described in "To configure the FFT
setup" on page 196.
To configure the FFT setup
1. Select the "FFT Setup" tab of the "Math" dialog box.
2. By default, a suitable frequency range for the expected horizontal values according
to the resolution bandwidth is selected, in respect to performance and precision. Span
and RBW settings are coupled. If a more precise evaluation is required, for example
for postprocessing in a different application, disable the coupling and change the
frequency ranges and resolution bandwidth values as required.
a) Disable the "Span/RBW coupling".
b) Specify the frequency range to be displayed using one of the following methods:
● Enter a "Center frequency" and a "Frequency span" that define the spectrum.
● 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.
c) Change the "Span/RBW ratio". The smaller the ratio, the higher the RBW
becomes to display the same frequency span.
FFT Analysis