Math FFT
This chapter contains detailed information on how to use the Math FFT (Fast
Fourier Transform). You can use the FFT Math mode to convert a time-domain
(YT) signal into its frequency components (spectrum). You can use the Math FFT
mode for the following types of analysis:
Analyze harmonics in power lines
Measure harmonic content and distortion in systems
Characterize noise in DC power supplies
Test impulse response of filters and systems
Analyze v
ibration
To use the Math FFT mode, you need to perform the following tasks:
Set up the source (time-domain) waveform
Display the FFT spectrum
Select a type of FFT window
Adjust the sample rate to display the fundamental frequency and harmonics
without aliasing
Use zoom controls to magnify the spectrum
Use c
ursors to measure the spectrum
SettingUptheTime-DomainWaveform
Bef
ore you use FFT mode, you need to set up the time-domain (YT) waveform.
To do so, follow these steps:
1. Pu
sh AutoSet to display a YT waveform.
2. Turn the vertical Position knob to move the YT waveform to the center
v
ertically (zero divisions).
This ensures that the FFT will show a true D C v alue.
3. Turn the Horizontal Position knob to position the part of the YT waveform
that you want to analyze in the center eight divisions of the screen.
The oscilloscope calculates the FFT spectrum using the center 2048 points of
the time-domain waveform.
TDS2000C and TDS1000C-EDU Series Oscilloscope User Manual 55
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