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Fast Fourier Transforms
TDS 620A, 640A, & 644A User Manual
Hamming — Very good window for resolving frequencies that are
very close to the same value with somewhat improved amplitude
accuracy over the rectangular window.
Hanning — Very good window for measuring amplitude accuracy
but degraded for resolving frequencies.
Blackman-Harris — Best window for measuring the amplitude of
frequencies but worst at resolving frequencies.
The topic
Selecting the Window,
on page 3-51, provides in depth informa-
tion on choosing the right window for your application.
9. If you did not select Phase (deg) or Phase (rad) in step 7, skip to
step 12. Phase suppression is only used to reduce noise in phase FFTs.
10. If you need to reduce the effect of noise in your phase FFT, press Sup-
press phase at amplitudes < (side).
11. Use the general purpose knob (or the keypad if your oscilloscope is so
equipped) to adjust the phase suppression level. FFT magnitudes below
this level will have their phase set to zero.
The topic
Adjust Phase Suppression,
on page 3-50, provides additional
information on phase suppression.
12. Press OK Create Math Wfm (side) to display the FFT of the waveform
you input in step 1 (see Figure 3-22).
Figure 3-22: FFT Math Waveform in Math1