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V5.1‐March2010
Figure 41
Selecting an FFT Window
■ The FFT feature provides four (4) windows. Each is a trade-off between frequency
resolution and magnitude accuracy. What is measured and what the source signal
characteristics are help determine which window to use. Use the following guidelines
to select the best window.
Type Description Window
Rectangle
Rectangle is the ideal window type for resolving
frequencies that are very close to the same value
but least desirable for accurately measuring the
amplitude of those frequencies. It is the ideal type
for measuring the frequency spectrum of aperiodic
signals and measuring frequency components near
DC.
Use rectangle for measuring transients or surges
where the signal level before and after the event
are nearly equal. Also, use this window for equal-
amplitude sine waves with frequencies that are
very close and for broadband random noise with a
relatively slow varying spectrum.
