UTD4000 Four-channel User Manual
28
Select the FFT Window
Assuming the YT waveform is constantly repeating
itself, the oscilloscope will carry out FFT conversion
of time record of a limited length. When this cycle is a
whole number, the YT waveform will have the same
amplitude at the start and finish. There is no
waveform interruption. However, if the YT waveform
cycle is not a whole number, there will be different
amplitudes at the start and finish, resulting in
transient interruption of high frequency at the
connection point. In frequency domain, this is known
as leakage. To avoid leakage, multiply the original
waveform by one window function to set the value to 0
for start and finish compulsively. For application of the
window function, please see the table below :
How to use FFT functions
Signals with DC quantities or DC offset will cause
error or offset of FFT waveform quantities. To reduce
DC quantities, select AC
coupling
To
reduce
random noise and frequency aliasing resulted by
repeated or single pulse event
set the acquiring
mode of your oscilloscope to average acquisition.
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