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The oscilloscope’s vertical response is a little bit larger than its bandwidth (60MHz, 70MHz, 100MHz
,
200MHz or
300MHz, depending on the model; or 20MHz when the Bandwidth Limit option is set to Limited). Therefore, the FFT
spectrum can display valid frequency information above the oscilloscope bandwidth. However, the amplitude
information near or above the bandwidth will not be accurate.
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, Bartletta and
Blackman
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
