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 :
Table 2-3 Explanatory notes for the FFT menu
Function Menu Setup Explanatory Note
Type FFT To carry out FFT algorithm
functions
Set CH1 as math waveform
Set CH2 as math waveform
Ch1
Ch2
Source
Window
Hanning
Hamming
Blackman
Rectangle
Set Hanning window function
Set Hamming window function
Set Blackman window function
Set Rectangle window function
Set the vertical unit to Vrms or
dBVrms
Vrms
dBVrms
Vertical
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.
31
DSO Series User Manual
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