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Fast Fourier Transforms
Reference
Figure 3-21: Define FFT Waveform Menu
5. If the selected math waveform is not FFT, press Change Math Definition
(side) ➞ FFT (main). See Figure 3-21.
6. Press Set FFT Source to (side) repeatedly until the channel source
selected in step 1 appears in the menu label.
7. Press Set FFT Vert Scale to (side) repeatedly to choose from the follow-
ing vertical scale types:
dBV RMS — Magnitude is displayed using log scale, expressed in dB
relative to 1 V
RMS
where 0 dB =1 V
RMS
.
Linear RMS — Magnitude is displayed using voltage as the scale.
Phase (deg) — Phase is displayed using degrees as the scale,
where degrees wrap from –180 to +180 .
Phase (rad) — Phase is displayed using radians as the scale, where
radians wrap from – to + .
The topic
Considerations for Phase Displays,
on page 3-49, provides in
depth information on setup for phase displays.
8. Press Set FFT Window to (side) repeatedly to choose from the following
window types:
Rectangular — Best type for resolving frequencies that are very
close to the same value but worst for accurately measuring the
amplitude of those frequencies. Best type for measuring the frequen-
cy spectrum of non-repetitive signals and measuring frequency
components near DC.