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Math Operation
•
Start-End (start frequency to stop frequency): Start frequency specifies the
frequency at the left side of the display. Click or tap the Start input field to set
the start frequency with the pop-up numeric keypad or use the corresponding
multipurpose knob to set the value. Its range is from 0 Hz to (stop frequency-10
Hz). Stop frequency specifies the frequency at the right side of the display. Click
or tap the End input field to set the stop frequency with the pop-up numeric
keypad or use the corresponding multipurpose knob to set the value. Its range is
from (start frequency+10 Hz) to 1 GHz. By default, it is 10 MHz.
Vertical Scale/Offset
In Unit item, you can select dBm/dBV or Vrms as the unit for Scale and Offset.
For how to set the Scale, refer to the descriptions in
how to set the Offset, refer to the descriptions in
Window Function
Spectral leakage can be considerably minimized when a window function is used. The
oscilloscope provides 6 FFT window functions which have different characteristics and
are applicable to measure different waveforms, as shown in the table below. You need
to select the window function according to the characteristics of the waveform to be
measured. Click or tap the Window drop-down button to select the desired window
function.
Table 9.1 Window Function
Window
Function
Rectangular
Blackman-
Harris
HDO4000 User Guide
138
Characteristics
Best frequency resolution
Poorest amplitude resolution
Similar to the situation when no
window is applied.
Best amplitude resolution
Poorest frequency resolution
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Scale
"Arithmetic Operation". For
Offset
in "Arithmetic Operation".
Waveforms Applicable to the
Window Function
Transient or short pulse, the
signal levels before and after the
multiplication are basically the
same
Sine waveforms with the same
amplitudes and rather similar
frequencies
Wide band random noise with
relatively slow change of
waveform spectrum
Single frequency signal,
searching for higher order
harmonics
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