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5.3.1.2
Displaying FFT Spectrum
Push the MATH MENU button to display the Math menu. Use the options to select the Source channel, the Window
algorithm and the FFT Zoom factor. Only one FFT spectrum can be displayed at a time.
Math FFT Options
Settings
Comments
Source
CH1, CH2
Choose a channel to be the FFT source.
Window
Hanning, Flattop,
Rectangular
Select a type of the FFT window. For more information, refer to
5.3.1.3
.
FFT Zoom
X1, X2, X5, X10
Change the horizontal magnification of the FFT display. For detailed
information, refer to
Vertical Base
Vrms
dBrms
Set the Vertical Base in a mode.
1.
Frequency at the center graticule line
2.
Vertical scale in dB per division (0dB=1V
RMS
)
3.
Horizontal scale in frequency per division
4.
Sample rate in number of samples per second
5.
FFT window type
5.3.1.3
Selecting FFT Window
Using windows can eliminate the spectral leakage in the FFT spectrum. The FFT algorithm assumes that the YT
waveform repeats all the time. When the number of cycles is integral (1, 2, 3 ...), the YT waveform starts and ends at
the same amplitude and there are no discontinuities in the signal shape.
If the number of cycles is nonintegral, the YT waveform starts and ends at different amplitudes and transitions
between the start and end points will cause discontinuities in the signal that introduces high-frequency transients.
