Operating Instructions
1720/1721
2–15
8. Variable
With the test circle displayed, push the VARIABLE push button and check that
the VARIABLE ON indicator lights.
Rotate the VARIABLE control fully clockwise and check that the display
increases in size.
Rotate the VARIABLE control fully counterclockwise and check that the outer
circle is inside the outer (Red and Cyan) targets.
Push the VARIABLE push button and check that the test circle is on the outer
targets and that the front-panel VARIABLE ON indicator is off.
9. Check the Rotation of the Display
Variations in the earth’s magnetic field may make adjustment of the ROTATE
control necessary at installation time or whenever the instrument is moved.
Connect the audio signal, through the XY INPUT connector on the rear panel, to
the +X input (pin 3). Set the 1720/1721 MODE to XY. Set up the audio signal
amplitude for a horizontal trace that is long enough to reach across the graticule
compass rose.
Check that the sweep is a straight line parallel to the horizontal axis. If not,
adjust the ROTATE adjustment until the sweep is parallel to the horizontal axis.
10. Check XY Mode
Connect the audio signal to both pins 3 and 7 of the rear-panel XY INPUT. Set
the 1720/1721 MODE to XY. Adjust the audio signal amplitude to place the
diagonal trace on the 45° graticule line. Adjust audio signal amplitude so that
the ends of the trace fall on the target (+) marks.
11. Check Dual Mode
Select INPUT A. With the color bar composite video signal connected to the
CH-A INPUT and the audio signal connected to the XY INPUT (pins 3 and 7)
push and hold the MODE push button until both VECT and XY are lit. Check
for a display of both vectors and the XY lissajous.
Measurement Applications
The 1720/1721 is unique in that it is a vectorscope capable of making both
chrominance and XY measurements. The information that follows is intended to
guide both new and experienced users through simple and complex measurement
techniques. The information is divided by major topics, which are then
subdivided into specific measurements.
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