FFT
The 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 and your source signal characteristics will help you to
determine w hich 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 g reater than the Nyquist frequency.
(See page 52, 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.
TBS1000B and TBS1000B-EDU Series Oscilloscopes User Manual 55
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