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Applications
R&S
®
RTA4000
174
User Manual 1335.7898.02 ─ 08
1 = Enable FFT
2 = Signal vs. time display
3 = FFT parameters
4 = Spectrum, result of the FFT analysis
5 = FFT label with vertical scale (range per division). Color indicates the source waveform of FFT calcula-
tion.
Data source
FFT analysis is performed on the data captured from one of the active input channels,
or one of the active math or reference waveforms. Analysis can only be performed on
one channel at a time.
Timebase
FFT is performed on the captured data of a complete acquisition. To reduce calculation
time, the instrument automatically sets the time scale (and thus the acquisition time),
and an extract of the timebase for which the FFT is calculated. This time gate is indica-
ted by white lines in the time diagram.
Frequency range
The results of the FFT analysis are restricted to a specified frequency range. There-
fore, you define a center frequency and a frequency span, or the start and stop fre-
quencies. Alternatively, you can manually set the resolution bandwidth (RBW). When
you change the frequency parameters, the timebase and time gate on the waveform is
adapted automatically. Changing the RBW affects the time gate.
FFT analysis