HP 54750A, User Manual, Page: 276 / 478

General Purpose Oscilloscope Menus
FFT Menu
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Window
The three FFT windows you can select from are:
rectangular
Hanning
attop
The FFT operation assumes the time record repeats innitely . Unless there
is an integral number of cycles of the sampled waveform in the record,
a discontinuity is created at the end of the record. This is referred to as
leakage . In order to minimize spectral leakage , windows that approach zero
smoothly at the beginning and end of the record are employed as lters to the
FFT .
Windows work by weighting points in the middle of the waveform record
higher than those at the ends of the record. F or example , a Hanning window
looks like the rst half of a sine wave . The Hanning window multiplies the
points in the center of the record by 1 and multiplies the points at the start
and the end of the record by zero .
The rectangular window is essentially no window . All points in the record are
multiplied by 1. The rectangular window is useful for transient signals and
signals where there are an integral number of cycles in the time record.
The Hanning window is useful for frequency resolution and general-purpose
use . It is good for resolving two frequencies that are close together or for
making frequency measurements .
The attop window is the best window for making accurate amplitude
measurements of frequency peaks .
K ey Path 4 FFT 5
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Window
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