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Performance Verification
1780R-Series Service Manual
4–59
d. Set the 1780R-Series VECTOR GAIN to VAR. Turn the variable
VECTOR GAIN control counterclockwise until the circle is its smallest
size.
e. Note the amplitude of the display on the Waveform CRT.
f. Set the generator output amplitude so that it is twice the amplitude noted
in part e. of this step. Note this amplitude on the Waveform CRT.
g. Check that the circle is located inside the compass rose.
h. Adjust the generator output amplitude so that it is 1/10 the amplitude
noted in part f. of this step.
i. Turn the variable VECTOR GAIN control clockwise until the circle is its
largest size.
j. Check that the circle is located outside the compass rose.
k. Select VECTOR GAIN–MAX on the 1780R-Series front panel.
l. Check that the circle is located outside the compass rose.
m. Set VECTOR GAIN–MAX to Off.
n. Disconnect the sine wave signal and minimum loss attenuator from the
instrument.
53. Check Variable Gain Phase Shift
Requirement: Phase Shift: ±1_ as gain is varied from +3 dB to –6 dB.
a. Connect the television test signal generator Color Bar signal to the
1780R-Series CH A INPUT connector. Check that a 75 W feed-through
terminator is connected to this loop-through connector.
b. Set the 1780R-Series controls as follows: Press the MEASURE button to
On. Select DIFF PHASE and SINGLE on the menu.
c. Turn the Precision Measurement control to null the burst displayed on
the Waveform CRT. Check that the burst vector is located on the 180_
graticule line as displayed on the Vectorscope CRT. (For PAL, use the
135_ burst vector when performing parts c. through h.)
d. Press the REFERENCE SET button.
e. Select VECTOR GAIN–VAR mode. Adjust the variable VECTOR
GAIN control so that the burst vector is one-half its original length.
f. Turn the Precision Measurement control to null the burst.
g. Check that the PHASE readout on the Vectorscope CRT is between
+1.00_ and –1.00_.