Tektronix WCA200A, User Manual

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WCA230A & WCA280A User Manual
3- 173
FFT and RBW
An input signal is converted to the frequency domain data by FFT (Fast Fourier
Transform) processing. RBW (Resolution Bandwidth) processing is then applied,
for compatibility with measurement data from conventional swept spectrum
analyzers (see Figure 3--122). Moreover, the Real Time S/A mode has FFT
overlap capability.
NOTE
. You can set the FFT and RBW parameters in the S/A (spectrum analysis)
mode. In the Demod (modulation analysis) and Time (time analysis) modes, the
number of FFT points is always 1024 and the window is always Blackman-Har-
ris 4B type. However, for the pulse measurements in the Time mode, you can
select Nyquist or Blackman-Harris 4B (refer to
RBW/FFT Menu on page 3--97).
The Demod and Time modes have no RBW process.
The adjustable parameters for FFT are:
H
FFT points
H
FFT window
H
FFT start point (Real Time S/A only)
The adjustable parameters for RBW are:
H
Resolution bandwidth (RBW)
H
Filter shape
H
Roll-off ratio (for the Nyquist or Root Nyquist filter)
FFT RBW
Time domain data
after A/D conversion
Frequency
domain
data
Measurement
and display
Parameters
S
FFT points
S
FFT window
S
FFT start point
Parameters
S
RBW
S
Filter shape
S
Roll-off ratio
* FFT points is normally set automatically with the RBW setting.
RBW is normally set automatically with the span setting.
Figure 3- 122: FFT and RBW process