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 which window to use.
Window
Measure
Characteristics
Hanning
Periodic waveforms
Better frequency, poorer magnitude
accuracy than Flattop
Flattop
Periodic waveforms
Better magnitude, poorer frequency
accuracy than Hanning
Rectangular
Pulses or transients
Special-purpose window for waveforms
that 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 52,
.) The frequency components that are above the
Nyquist frequency are undersampled, appearing as lower frequency components
that "fold back" around the Nyquist frequency. These incorrect components are
called aliases.
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