C–12
Appendix C
Additional Processing Other waveform processing functions, such as Averaging and
Arithmetic, can be applied to waveforms before FFT processing
is performed. Time-domain averaging prior to FFT, for example,
can be used if a stable trigger is available to reduce random
noise in the signal.
Memory Status When FFT is used, the field beneath the grid displays
parameters of the waveform descriptor, including number of
points, horizontal and vertical scale factors and units.
Using Cursors with FFT For reading the amplitude and frequency of a data point, the
Absolute Time cursor can be moved into the frequency domain by
going beyond the right-hand edge of a time-domain waveform.
The Relative Time cursors can be moved into the frequency
domain to simultaneously indicate the frequency difference and
the amplitude difference between two points on each frequency-
domain trace.
The Absolute Voltage cursor reads the absolute value of a point
in a spectrum in the appropriate units, and the Relative Voltage
cursors indicate the difference between two levels on each trace
Note:
Ø To increase the FFT frequency range, the Nyquist
frequency, raise the effective sampling frequency by
increasing the maximum number of points or using a
faster time base.
Ø To increase the FFT frequency resolution, increase the
length of the time-domain waveform record by using a
slower time base.
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