Fft Menu; Display; Source; Window - HP 54710A User's Reference Manual

FFT Menu

Display

Display

The Display softkey turns the FFT function on and off. When on, the FFT
Scaling softkey is displayed and a new waveform is displayed on the screen
corresponding to the FFT function. This FFT waveform is displayed in the
same color used to represent waveforms on slot 3, and the default color is
purple.

Source

The Source softkey determines which signal the oscilloscope uses to generate
the FFT function. You can select any channel, function, memory, or a
constant as the source of the FFT function.

Window

The three FFT windows you can select from are rectangular, Hanning, and
flattop. The FFT operation assumes that the time record repeats infinitely.
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 filters
to the FFT.
Windows work by weighting points in the middle of the waveform record
higher than those at the ends of the record. For example, a Hanning window
looks like the first 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 flattop window is the best window for making
accurate amplitude measurements of frequency peaks.
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