FFT Spectral Analysis 4
Keysight InfiniiVision 3000T X-Series Oscilloscopes User's Guide 93
• “FFT Aliasing" on page 95
• “FFT Spectral Leakage" on page 97
• “Units for Math Waveforms" on page 101
Searching for FFT Peaks
To search for FFT math function frequency peaks:
1 Press [Search].
2 In the Search Menu, press Search; then, turn the Entry knob to select Frequency
Peaks.
3 Press Source and select the FFT math function waveform to search.
4 Press Max # Peaks and specify the maximum number of FFT peaks to find.
5 Press Threshold and turn the Entry knob to specify the threshold level necessary
to be considered a peak.
6 Press Excursion to specify the amplitude above the FFT waveform's noise floor
necessary to be recognized as a peak.
Note that the FFT waveform's noise floor level differs when additional math
functions are applied to the FFT:
• When Averaged Value, Max Hold, or Min Hold are applied, the FFT waveform's
noise floor is more stable, and excursion level settings are more accurate.
• When no additional math functions are applied (normal), the FFT waveform's
noise floor is less stable and excursion level settings are less accurate.
White arrowheads at the top of the graticule show where FFT peaks are found.
When acquisitions are stopped, you can use the [Navigate] keys and cursors to look
at the search events found.
FFT Measurement Hints
The number of points acquired for the FFT record can be up to 65,536, and when
frequency span is at maximum, all points are displayed. Once the FFT spectrum is
displayed, the frequency span and center frequency controls are used much like
the controls of a spectrum analyzer to examine the frequency of interest in greater
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