218 6000 Series Oscilloscope User’s Guide
5 Making Measurements
Spectral Leakage
The FFT operation assumes that the time record repeats.
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 signal are
employed as filters to the FFT. The FFT menu provides three
windows: Hanning, flattop, and rectangular. For more
information on leakage, see Agilent Application Note 243,
“The Fundamentals of Signal Analysis” at
http://cp.literature.agilent.com/litweb/pdf/5952-8898E.pdf.
FFT Operation
1 Press the Math key, then press the FFT softkey to display
the softkeys for FFT settings.
• Source — selects the source for the FFT. The source can
be any analog channel, or math functions 1 + 2, 1 – 2,
and 1 * 2.
• Span — sets the overall width of the FFT spectrum that
you see on the display (left to right). Divide span by 10
to calculate the number of Hertz per division. It is
possible to set Span above the maximum available
frequency, in which case the displayed spectrum will
not take up the whole screen. Press the Span softkey,
then turn the Entry knob to set the desired frequency
span of the display.
Source
select
Frequency
Span
Center
frequency
Preset Span
and Center
frequencies
Vertical and
Window FFT
controls
Sample
rate
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