User manual

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 s ystems
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 Y T 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 Y T 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.
TBS1000 Series Oscilloscopes User Manual 55