222 6000 Series Oscilloscope User’s Guide
5 Making Measurements
FFTs ability to resolve two closely space frequencies. A good
way to test the ability of the FFT to resolve two closely
spaced frequencies is to examine the sidebands of an
amplitude modulated sine wave.
For the best vertical accuracy on peak measurements:
• Make sure the probe attenuation is set correctly. The
probe attenuation is set from the Channel menu if the
operand is a channel.
• Set the source sensitivity so that the input signal is near
full screen, but not clipped.
• Use the Flat Top window.
• Set the FFT sensitivity to a sensitive range, such as
2dB/division.
For best frequency accuracy on peaks:
• Use the Hanning window.
• Use Cursors to place an X cursor on the frequency of
interest.
• Adjust frequency span for better cursor placement.
• Return to the Cursors menu to fine tune the X cursor.
For more information on the use of FFTs please refer to
Agilent Application Note 243, ”The Fundamentals of Signal
Analysis” at
http://cp.literature.agilent.com/litweb/pdf/5952-8898E.pdf.
Additional information can be obtained from Chapter 4 of
the book “Spectrum and Network Measurements” by Robert
A. Witte.
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