Basics on I/Q Data Acquisition and Processing
R&S
®
FSV/A3000 I/Q
Analyzer
40
User Manual 1178.8536.02 ─ 01
duration of the calculation. The size of the window can be defined manually according
to the record length, the overlap factor, and the FFT length.
An FFT overlap of 67%, for example, means the second FFT calculation uses the last
67% of the data of the first FFT. It uses only 33% new data. The third FFT still covers
33% of the first FFT and 67% of the second FFT, and so on.
Figure 4-6: Overlapping FFTs
In "Manual" or "Auto" FFT mode, an FFT length of 4096 and a window length of 4096
(or the record length, if shorter) is used to calculate the spectrum.
Combining results - trace detector
If the record length permits, multiple overlapping windows are calculated and combined
to create the final spectrum using the selected trace detector. If necessary, the trace
detector is also used to reduce the number of calculated frequency points (defined by
the FFT length) to the defined number of sweep points. By default, the Autopeak trace
detector is used.
Since the frequency points are reduced to the number of sweep points, using a detec-
tor other than "Auto Peak" and fewer than 4096 sweep points can lead to false level
results.
Basics on FFT
