Math FFT
122 TDS1000/2000-Series Digital Oscilloscope User Manual
The Math FFT function includes three FFT Window options. There is
a trade-off betweenfrequency resolution and amplitude accuracy
with each type of window.What you want to measure and your
source signal characteristics hel p you to determine which window to
use.
Window Measure Characteristics
Hanning Periodic
waveforms
Better frequency,poorer magnitude
accuracy than Flatto p
Flattop Periodic
waveforms
Better magnitude, poorer frequency
accuracy than Hanning
Rectangular Pulses or
transients
Special-purpose window for waveforms that
do not have discontinuities. Thisis essential-
ly the same as no window
FFT Aliasing
Problems occurwhen the oscilloscope acquires a time-domain
waveform containing frequency compone nts that are greater than the
Nyquist frequency (refer to Nyquist Frequency on page 117). The
frequency components that are above the Nyquist frequency are
undersampled, appearing as l ower frequency components that “fold
back”around the Nyquist frequency. These incorrect components are
called aliases.