Fast Fourier Transforms
TDS 620A, 640A, & 644A User Manual
3Ć39
zontal scale for FFT math waveforms is always expressed in frequency per
division with the beginning (left-most point) of the waveform representing zero
frequency (DC).
The FFT waveform is based on digital signal processing (DSP) of data, which
allows more versatility in measuring the frequency content of waveforms. For
example, DSP allows the oscilloscope to compute FFTs of source waveforms
that must be acquired based on a single trigger, making it useful for measur-
ing the frequency content of single events.
Normal Waveform of
an Impulse Response
FFT Waveform of the
Magnitude Response
FFT Waveform of the
Phase Response
Figure 3-20: System Response to an Impulse
To obtain an FFT of your waveform:
1. Connect the waveform to the desired channel input and select that chan-
nel.
2. Adjust the vertical and horizontal scales and trigger the display (or press
AUTOSET).
The topic
Offset, Position, and Scale,
on page 3-46, provides in depth
information about optimizing your setup for FFT displays.
3. Press MORE to access the menu for turning on math waveforms.
4. Select a math waveform. Your choices are Math1, Math2, and
Math3 (main).
Operation
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