Agilent Technologies 6000 Series User Manual page 6

5 Making Measurements
172
• Center — sets the FFT spectrum frequency represented at
the center vertical grid line of the display. It is possible to
set the Center to values below half the span or above the
maximum available frequency, in which case the displayed
spectrum will not take up the whole screen. Press the
Center softkey, then turn the Entry knob to set the desired
center frequency of the display.
Preset — sets the frequency Span and Center to values that
•
will cause the entire available spectrum to be displayed.
The maximum available frequency is half the effective FFT
sample rate, which is a function of the time per division
setting. The current FFT sample rate is displayed above
the softkeys.
2 Press the More FFT softkey to display additional FFT
settings.
FFT Scale FFT Offset
• Scale — lets you set your own vertical scale factors for FFT
expressed in dB/div (decibels/division). Press the Scale
softkey, then turn the Entry knob to rescale your math
function.
• Offset — lets you set your own offset for the FFT. The offset
value is in dB and is represented by the center horizontal
grid line of the display. Press the Offset softkey, then turn
the Entry knob to change the offset of your math function.
Scale and offset considerations
If you do not manually change the FFT scale or offset settings, when you turn the
horizontal sweep speed knob, the span and center frequency settings will
automatically change to allow optimum viewing of the full spectrum. If you do
manually set scale or offset, turning the sweep speed knob will not change the
span or center frequency settings, allowing you see better detail around a specific
frequency. Pressing the FFT Preset softkey will automatically rescale the
waveform and span and center will again automatically track the horizontal
sweep speed setting.
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