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FFTAUTO
Marker to Auto FFT
Performs a fast Fourier transform (FIT) on the signal on which the marker is placed.
Syntax
Equivalent Softkey: MARKER
->
AUTO
FFT .
Prerequisite Commands: Use a marker command to place a marker on the signal of interest.
See
YIhble
5-4 for a list of the marker commands.
Related Commands:
FFI’CONTS,
FFTOFF, FFTSNGLS.
Example
This example can be used to perform an
FF”I’
continuously on an amplitude modulated signal at
100 MHz.
OUTPUT
718*"RL
ODB-"
OUTPUT
718&F
100ilHZ;"
Sets reference level to 0 dBm.
Sets the center
frequency
to 100 MHz.
OUTPUT
718."SP
IOMHZ-"
,
t
Decreases the
freqwncg
span.
OUTPUT
718."MKPK
HI-"
, ,
Places the marker on a signal (this example
oxwnes
that there
is only one signal present).
OUTPUT
718;"FFTAUTO;"
Zoom in on the
sip&,
and then does an FFT continuously
on the modulated
siml.
Description
FFTAUTO uses the marker’s position to determine which signal is to be measured. FFIAUTO
centers the signal and, if the frequency span of the spectrum analyzer is greater than zero,
decreases the frequency span to zero before performing an FFT on the signal. When the FFT is
performed, the spectrum analyzer does the following:
n
Changes to the continuous sweep mode.
n
Changes to the linear amplitude scale.
n If the current detector is the peak detector, changes to the sample detector.
n If the initial frequency span was greater than 0 Hz, the spectrum analyzer adjusts the signal
peak to within 0.5 division of the top graticule.
n Does an FFT on trace A and then places trace A in both the clear-write and store-blank
modes. (When the spectrum analyzer is in both the clear-write and store-blank modes, the
trace data is still taken from the spectrum analyzer input during every measurement sweep,
but the trace is
not
shown on the spectrum analyzer display.)
n Places the results of the FFT in trace B, and then changes trace B to the view mode.
FFTAUTO performs the FFT on the signal at the end of every sweep. After executing
FFTAUTO, you should adjust the values for the resolution bandwidth, video bandwidth,
and sweep time according to the highest modulation frequency of interest. The resolution
bandwidth should be about ten times greater than the highest modulation frequency of
interest, and the video bandwidth should be about 10 times higher than the highest modulation
frequency of interest. The sweep time should be set according to the chart shown in
5-l
64 Programming Commands