Math FFT
116
TDS1000/2000-Series Digital Oscilloscope User Manual
Setting Up the Time-Domain Waveform
Before you use FFT mode, you need to set up the time-domain (YT)
waveform. To do so, follow these steps:
1. Push AUTOSET to displa y a YT waveform.
2. Turn the VERTICAL POSITION knob to move the YT
waveform to the center vertically (zero divisions).
This ensures that the FFT will show a true DC value.
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.
4. Turn the VOLTS/DIV knob to ensure that the entire waveform
remains on the screen. The oscilloscope may display erroneous
FFT results (by adding high frequency components) if t he entire
waveform is not visible.
5. Turn the SEC/DIV knob to provide the resolution you want i n the
FFT spectrum.
6. If possible, set the oscilloscope to display many signal cycles.
If you turn the SEC/ DIV knob to select a faster se tting (fewer
cycles), the FFT spectrum shows a larger frequency range, and
reduces the possibility of FFT aliasing, described on page 122.
However, the oscilloscope also displays less frequency resolution.
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