h. Adjust X1 ADJ potentiometer R13 to produce a
Panoramic Indicator IP-173/U and obtain an indication
reading of 1/10 full scale at the external voltmeter.
of the carrier on the screen.
e. Rotate the DEVIATION control until the carrier
86. Adjustment of Bias Potentiometer for Minimum
goes through the second null. (This represents a 1lO-kc
RF Distortion
deviation.) Note the reading of the KILOCYCLES
Warning: Adjust the bias potentiometer only when L1
DEVIATION meter.
has been replaced. When bias potentiometer RO1O is
adjusted it is necessary to repeat the steps in paragraph
the procedure given in c, d, and e above.
a. Connect the following equipment to the R. F.
g. If the new reading of the KILOCYCLES
OUTPUT jack of Signal Generator SG-3/U (fig. 40).
DEVIATION meter is more than 5 percent, different
(1) Radio Receiver R274/FRR.
from the previous reading, readjust R65 slightly, noting
the direction of rotation.
(2) Spectrum Analyzer TS-723/U.
h. Repeat the procedure given in b through f
b. Adjust Signal Generator SG-3/U as follows:
above.
(1) Set the MODULATION selector to 1000 -.
i. If the difference between the 50- and 100-mc
(2) Place the FREQ. RANGE-MC switch in
readings is greater than previously, readjust R65 in the
the 100-200 me position. Adjust the
opposite direction.
TUNING control until the FREQ. IN
j. Repeat procedure given in b through g above
MEGACYCLES dial indicates 50 mc.
until the difference between the 50- and 100-mc
(3) Set the DEVIATION control to produce a
readings is less than 5 percent.
full-scale reading on the KILOCYCLES
k. Readjust DEV CAL potentiometer R6 until the
DEVIATION meter.
KILOCYCLES DEVIATION meter indicates 110 kc with
(4) Adjust bias potentiometer R100 for
the carrier in the second null.
minimum second harmonic distortion.
l. Disconnect the panoramic indicator.
deviation compensation, and deviation calibration
85. Calibrating Deviation Multiplier
adjustment (par. 84).
a. Connect an accurate vacuum-tube voltmeter
(Electronic Multimeter TS-505/U) to the green lead
Note. In an emergency, if rf distortion measuring
connecting S1 to C70 or to C67. When measuring
equipment is not available, a dc milliammeter may be
unknown voltages, select the highest scale to protect the
used for indicating the approximate correct setting of
meter.
R10(#. Unsolder either lead of R100 and insert a de
milllammeter (0- to 20-ma range) across the open
b. Set the MODULATION selector to 1000 -.
connection. Adjust R100 to produce a meter reading of
c. Set the DEV MULT switch to the X10 position.
9 ma. Disconnect the meter and resolder the lead.
d. Set the DEVIATION control to produce a full-
Recheck as in c above.
scale reading at the external voltmeter, on any
convenient scale.
87. Deviation Frequency Compensation
e. Set the DEV MULT switch to the X5 position.
f. Adjust X5 ADJ potentiometer R8 to produce a
C49 only when L1 has been replaced.
reading of Y2 scale at the external voltmeter.
g. Set tile DEV MULT switch to X1 scale.
Figure 40. Rf distortion test setup.
62
