Math FFT
The Math FFT function includes three FFT Window options. There is a trade-off
between
frequency resolution and amplitude accuracy with each type of window.
What you want to measure a nd your source signal characteristics will help you to
determine which window to use.
Window Measur
e
Charac
teristics
Hanning
Perio
dic waveforms
Bette
r frequency, poorer magnitude
accuracy than Flattop
Flatt
op
Periodic waveforms Better magnitude, poorer frequency
accuracy than Hanning
Rectangular Pulses or transients
Special-purpose window for waveforms
tha
t do not have discontinuities. This is
essentially the same as no window
FFT Aliasing
Problems occur when the oscilloscope acquires a time-domain waveform
containing frequency components that are greater than the Nyquist frequency.
(See page 56, Nyquist Frequency.) The frequency components that are above the
Nyquist frequency are undersampled, appearing as lower frequency components
t
hat "fold back" around the Nyquist frequency. These incorrect components are
called aliases.
TDS2000C and TDS1000C-EDU Series Oscilloscope User Manual 59
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