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SIGLENT
26 SDS1000CFL User Manual
3. 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.
According to the tested options and source speciality, make sure the window
you need to use.
Table 2-11 FFT window instruction
Window Speciality Satisfied Test content
Rectangulr
Best frequency
resolution, worst
magnitude resolution.
This is essentially the
same as no window.
Symmetric transients or
bursts.
Equal-amplitude sine waves
with fixed frequencies.
Broadband random noise with
a relatively slowly varying
spectrum.
Hanning
Hamming
Better frequency, poorer
magnitude accuracy
than Rectangular.
Hamming has slightly
better frequency
resolution than Hanning.
Sine, periodic, and
narrow-band random noise.
Asymmetic transients or
bursts.
Blackman
Best magnitude, worst
frequency resolution.
Single frequency waveforms,
to find higher order harmonics.
4. Magnifying and Positioning an FFT Spectrum
You can magnify and use cursors to take measurements on the FFT spectrum.
The oscilloscope includes an “FFT Zoom” option to magnify horizontally, press
this option button to select “1X”, “2X”, “5X” or “10X”. Moreover, you also can turn
the “Universal” knob to magnify FFT waveform horizontally in a 1-2-5 step. To
magnify vertically; you can turn the “Volts/div” knob.
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