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164
The FFT Display
3.
Touch the {dB/div} scale tile at the bottom to
display its scale palette.
Touch
to auto scale the FFT.
Touch and drag in the graph area to move the
graph up and down or use the
buttons.
Use the <Cursor> knob to move the marker onto
the signal peak.
Touch
to change the width of the cursor. In
the FFT display, the wide cursors always find
the peak within the cursor region. This makes
reading an FFT much easier.
Touch the highlighted {dB/div} tile again to
dismiss the scale palette.
3.
Touch the {Hz/div} tile along the bottom to
display the span up/down buttons.
SR860 DSP Lock-in Amplifier
Use the <Cursor> knob to move the cursor.
The vertical axis is always logarthmic in the
FFT display. This allows a large dynamic range
to be shown in a single graph.
The amplitude is not calibrated.
and
Notice that the cursor readout at the upper right
reads the peak amplitude and frequency. This is
the signal from the external generator. The peak
is about −20 dB or 0.1 Vrms. The cursor reads
97.6562 kHz. This is because at this full span,
the FFT frequency bins are 9.76 kHz apart and
the 100.00 kHz signal falls mostly in the
97.6562 kHz bin.
The FFT frequency span can be reduced to
provide better frequency resolution. When the
FFT source is Raw ADC, the FFT display is
Appendix B
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