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8-Advanced Function of Oscilloscope
64
Figure 54 The Shown Frequency of M
Selecting an FFT Window
■ The FFT feature provides four windows. Each is a trade-off between frequency
resolution and magnitude accuracy. What you want to measure and your source signal
characteristics help determine which window to use. Use the following guidelines to
select the best window.
Type
Description
Window
Rectangle
This is the best type of window for resolving
frequencies that are very close to the same value
but worst for accurately measuring the amplitude of
those frequencies. It is the best type for measuring
the frequency spectrum of nonrepetitive signals and
measuring frequency components near DC.
Use r
ectangle for measuring transients or bursts
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.
Hamming
This is a very good window for resolving
frequencies that are very close to the same value
with somewhat improved amplitude accuracy over
the rectangle window. It has a slightly better
frequency resolution than the Hanning.
Use Hamming for measuring sine, periodic and
narrow band random noise. This window works on
transients or bursts where the signal levels before
and after the event are significantly different.
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