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 M
Ω
.
FFT units will be displayed in dBm when channel units is set to Volts and channel
impedance is set to 50
Ω
.
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.
