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Chapter 3 Demo Waveforms
Demo 2: Phase Modulation Analysis (BPSK)
This is a display of phase deviation from the constant reference frequency,
Fo = 100 kHz. The square wave modulation can easily be seen. Using the
cursor (left mouse button) and delta cursor (right mouse button) features,
you can easily determine the period of the modulation (1/mod rate), and
the peak-to-peak values.
DeTilt
Notice that the modulating signal has a "tilt" over time. This is because
the actual carrier is not exactly 100.0 kHz as we specified as the carrier
frequency on the Measure/View Setup menu. The DeTilt feature
provides a convenient way to fine tune this value of Fo to get a "flat"
display, and determine the precise value of the actual carrier frequency.
1
Position the cursor on one of the "high" phase states near the left side of
the plot (point A on the plot shown). Click on the left mouse button.
2
Re-position the cursor on another "high" phase state near the right side of
the plot (point B on the plot shown). Click on the left mouse button.
You have now defined two points which should be at the same vertical
level, but currently are not due to the "tilt" in the waveform.
3
Click on the DeTilt button. A warning message will appear indicating
that the value of Fo will be modified in the DeTilt process. Click OK to
acknowledge the warning. After a moment of recalculation, the graph will
be re-drawn with a slightly modified value of Fo. The tilt should be
removed. Note the new value of Fo (100.01 kHz instead of 100.0 kHz) on
the line just below the buttons. You can also verify Fo by clicking on the
Fo button and viewing the results log at the bottom of the display.
3-16
Getting Started Guide
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