35
Displaying the FFT Spectrum
Press the
MATH
button to display the Math Menu. Use the options to
select the Source channel, Window algorithm, and FFT Zoom factor. You
can display only one FFT spectrum at a time. You can select “Full screen”
or “Split” in “Display” option to display FFT waveform on full screen or
display channel waveform and its FFT waveform on half screen at a time.
Select FFT window
Windows reduce spectral leakage in the FFT spectrum. The FFT assumes
that the YT waveform repeats forever. With an integral number of cycles,
the YT waveform starts and ends at the me amplitude and there are no
discontinuities in the signal shape A non-integral number of cycles in the
YT waveform causes the signal start and end points to be at different
amplitudes. The transitions between the start and end points cause
discontinuities in the signal that introduce high-frequency transients.
Table 3.12 – FFT Window Description
Window
Characteristics
Applications
Rectangular
Best frequency
resolution, worst
magnitude resolution.
This is essentially the
Symmetric transients
or bursts. Equal-
amplitude sine waves
with fixed frequencies.