Basics on I/Q Data Acquisition and Processing
R&S
®
FSV/A3000 I/Q
Analyzer
41
User Manual 1178.8536.02 ─ 01
4.8.3
Dependencies Between FFT Parameters
FFT analysis in the R&S
FSV/A is highly configurable. Several parameters, including
the resolution bandwidth, record length, and FFT length, are user-definable. Note,
however, that several parameters are correlated and not all can be configured inde-
pendently of the others.
Record Length
Defines the number of I/Q samples to capture. By default, the number of sweep points
is used. The record length is calculated as the measurement time multiplied by the
sample rate.
If you change the record length, the
is automatically changed, as well.
For FFTs using only a single window ( "Single" mode), the record length (which is then
identical to the FFT length) must not exceed 512k.
FFT Length
Defines the number of frequency points determined by each FFT calculation. The more
points are used, the higher the resolution in the spectrum becomes, but the longer the
calculation takes.
In "Auto" or "Manual" mode, an FFT length of 4096 is used.
In advanced FFT mode, the FFT length is user-definable. If you use the arrow keys or
the rotary knob to change the FFT length, the value is incremented or decremented by
powers of 2. If you enter the value manually, any integer value from 3 to 524288 is
available.
If the FFT length is longer than the
the sample data is filled up with
zeros up to the FFT length. The FFT is then performed using interpolated frequency
points.
For an FFT length that is not a power of 2, a DFT (discrete Fourier transform) is per-
formed, which requires more time for calculation, but avoids the effects of interpolation.
To display all calculated frequency points (defined by the FFT length), the number of
sweep points is set to the FFT length automatically in advanced FFT mode.
Window Length
Defines the number of samples to be included in a single window in averaging mode.
(In single mode, the window length corresponds to the
Values from 3 to 4096 are available in "Manual" mode; in "Advanced" FFT mode, val-
ues from 3 to 524288 are available. However, the window length must not be longer
than the
.
If the window length is shorter than the
, the sample data is filled up with
zeros up to the FFT length.
If the window length is longer than the
(that is, not enough samples are
available), a window length the size of the
Basics on FFT