Digital Storage Oscilloscope 15
Zoom: Use the FFT Zoom button to adjust the
window size.
Scale: x1, x2, x5, x10.
Note: All selected menus are highlighted in orange.
2.7.2 Math FFT
This chapter elaborates how to use the Math FFT (Fast Fourier Transform). You can
use the Math FFT mode to convert a time-domain (YT) signal into its frequency
components (spectrum), and to observe the following types of signals:
Analyze harmonics in power cords;
Measure harmonic content and distortion in systems;
Characterize noise in DC power supplies;
Test impulse response of filters and systems;
Analyze vibration.
To use the Math FFT mode, perform the following tasks:
Set the source (time-domain) waveform;
Display the FFT spectrum;
Choose 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 cursors to measure the spectrum.
2.7.2.1 Setting Time-domain Waveform
It is necessary to set the time-domain (YT) waveform before using the FFT mode.
Follow the steps below.
1. Push the AUTOSET button to display a YT waveform.
2. Turn the VERTICAL POSITION knob to vertically move the YT waveform to the
center (zero division) so as to ensure the FFT will display a true DC value.
3. Turn the HORIZONTAL POSITION knob to position the part of the YT waveform to
be analyzed in the center eight divisions of the screen. The oscilloscope uses the
2048 center points of the time-domain waveform to calculate the FFT spectrum.
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