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Table 2-9 Page 2 of the function menu FFT:
FFT Option Setup Description
Vertical scale
Vrms
dBVrms
Set Vrms as vertical scale unit
Set dBVrms as vertical scale unit
Regulate FFT waveform spectrum amplitude
gear by [UNIVERSAL] knob
Regulate FFT waveform spectrum offset by
[UNIVERSAL] knob
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FFT Window
As the oscilloscope is used for FFT transformation on waveform recording with finite
length, the FFT algorithm is based on periodic signal. When the waveform period
number within the finite length is an integer, YT waveform has the same amplitude at
the start point and the end point, and no interruption is caused to the waveform. But
when the period number is not an integer, the waveform has different amplitude at the
start point and the end point, so that high-frequency transient interruption will be
caused in the joint. In a frequency domain, this effect is named as leakage. Therefore,
to avoid appearance of leakage, the original waveform is multiplied with a window
function, and forcibly make the values at the start point and the end point be 0.
Determine to use what kind of window according to the item and source signal
characteristics to be measured.
Table 2-10 Description of FFT window function
Window Characteristics Most suitable measuring points
Rectang
Best frequency resolution
Worst amplitude
resolution
Transient or short pulse where the
signal electric level is approximately
equal there-before and there-after;
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