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Figure 12 Performing an FFT math function on a repetitive digital clock.
You should now see a display similar to
displaying both a time domain waveform (Voltage versus Time) as well as
a frequency domain waveform (Power in units of dB versus Frequency).
An FFT math function breaks signals down into their individual sine wave
frequency components. All electrical signals, including digital signals, are
composed of multiple sine waves of different frequencies. An ideal clock
signal that has a 50% duty cycle should consist of a fundamental sine
wave frequency component (signal's repetitive frequency), plus its odd
harmonics (3rd, 5th, 7th, etc.). Note that non- ideal square waves will also
include lower- level even harmonics. Let's now verify the frequencies of the
fundamental and odd harmonics.
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2000 X-Series Oscilloscopes Advanced Training Guide
Set channel- 1's offset to approximately 1.00 V in order to center the
waveform on- screen.
Push the trigger level knob to set the trigger level at approximately 50%.
Set the timebase to 500.0 µs/div. At this timebase setting there will be
many cycles of the clock signal on- screen, which is typically required
when performing a precision FFT math function.
Press the [Math] front panel key; then press the Operator softkey.
Select the FFT math function using the Entry knob.
Press the [Cursors] front panel key (near the Cursors knob).
Press the Source softkey; then turn the Entry knob to change the Source
from channel- 1 to Math: f(t)
Push the Cursors knob and select the X1 cursor.
Oscilloscope Familiarization Labs
Figure
12. The scope is now
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