FFT Spectral Analysis 5
Keysight InfiniiVision 1200 X-Series and EDUX1052A/G Oscilloscopes User's Guide 61
• 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 2 dB/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 Keysight Application Note
243, The Fundamentals of Signal Analysis at
http://literature.cdn.keysight.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.
FFT Units
0 dBV is the amplitude of a 1 Vrms sinusoid. When the FFT source is channel 1 or
channel 2 (or channel 3 or 4 on 4-channel models), FFT units will be displayed in
dBV when channel units is set to Volts and channel impedance is set to 1 MΩ.
FFT units will be displayed in dBm when channel units is set to Volts and channel
impedance is set to 50Ω.
FFT units will be displayed as dB for all other FFT sources or when a source
channel's units has been set to Amps.
FFT DC Value
The FFT computation produces a DC value that is incorrect. It does not take the
offset at center screen into account. The DC value is not corrected in order to
accurately represent frequency components near DC.
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