User`s guide

Making Measurements 4
5000 Series Oscilloscope User’s Guide 167
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, press the FFT softkey, then press the
Settings softkey to display the FFT menu.
• Source — selects the source for the FFT. The source can be
any oscilloscope 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
Return to
previous menu
Center
frequency
Preset Span
and Center
frequencies
Vertical and
Window FFT
controls
Sample
rate