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Fast Fourier Transforms
Figure 3-17: FFT Math Waveform in Math1
Cursor Measurements of
an FFT
Once you have displayed an FFT math waveform, use cursors to measure its
frequency amplitude or phase angle.
1. Be sure MORE is selected in the channel selection buttons and that the FFT
math waveform is selected in the More main menu.
2. Press CURSOR ➞ Mode (main) ➞ Independent (side) ➞ Function (main) ➞ H Bars (side).
3. Use the general purpose knob to align the selected cursor (solid line) to the
top (or to any amplitude on the waveform you choose).
4. Press SELECT to select the other cursor. Use the general purpose knob to
align the selected cursor to the bottom (or to any amplitude on the waveform
you choose).
5. Read the amplitude between the two cursors from the D: readout. Read the
amplitude of the selected cursor relative to either 1 VRMS (0 dB), ground (0
volts), or the zero phase level (0 degrees or 0 radians) from the @: readout.
(The waveform reference indicator at the left side of the graticule indicates
the level where phase is zero for phase FFTs.)
TDS 420A, TDS 430A, TDS 460A & TDS 510A User Manual
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