Agilent Technologies 54657A Betriebsanweisung PDF herunterladen (Seite 26)

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

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.

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.

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

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Agilent Technologies 54657A Betriebsanweisung Seite 26