Agilent Technologies 54657A, User Manual

Page: 26 / 89

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
Measurement/Storage Module provides four windows: rectangular,
exponential, hanning, and flattop. For more information on leakage, see
Agilent Application Note 243, "The Fundamentals of Signal Analysis"
(Agilent part number 5952-8898.)
FFT Operation
1
Press
±
.
2
Toggle the
Function 2 On Off
softkey to enable math function number 2.
3
Press the Function 2 Menu softkey.
4
Toggle the
Operand
softkey until the desired source is selected.
F1 uses the result waveform in function 1.
5
Press the
Operation
softkey until FFT is selected. Results (F2) are
displayed on the screen.
6
Press the
Units/div
softkey and rotate the knob closest to the
Cursors
key to set the vertical sensitivity of the resulting
waveform.
7
Press the Ref Levl softkey and rotate the knob closest to the
Cursors
key to set the reference level (top graticule line) of
the resulting waveform.
The Autoscale FFT softkey will automatically set Units/div and Ref Levl to bring
the FFT data on screen. Frequency Span is set to maximum. Steps 6 and 7 could
be replaced to say:
6 Press FFT Menu softkey.
7 Press Autoscale FFT softkey. Rotate Time/Div knob until freq span is around
the frequencies of interest.
8
Press the
FFT Menu
softkey.
A softkey menu with six softkey choices appears. Five of them are related to
FFT.
Operating the Measurement/Storage Module
FFT Measurement
2–10