Section VI
Paragraphs 6-48 to 6-53
requires no additional setting of controls. These db
modulation using the same procedure as described in
adjustments may be checked at the AUDIO OUT con-
paragraph 6-46 above.
nector by turning the AUDIO SELECTOR to GLIDE
SLOPE and grounding the grid of the 150 cps stage
AND TONE LOCALIZER CENTERING.
(V1404, pin 2) while reading the 90 cps voltage; then
grounding the grid of the 90 cps stage (V1405, pin 2)
while reading the 150 cps voltage. The voltage ratios
a. Set the AUDIO SELECTOR in the 90~position.
obtained with the LOC-GS control set at the top line
Connect an ohmmeter scaled to read in the vicinity of
of each sector will be 1.41 to 1 instead of 2 to 1.
10,000 ohms between the center terminal of R1418A
and ground. (R1418A is the front section of the dual
LOC-GS potentiometer. ) Rotate the LOC-GS control
6-52. 9960 FM DEVIATION RATIO.
until the resistance reading is at a maximum. Loosen
the knob of the LOC-GS control and position it on the
shaft so that the knob points to the middle of the white
a. Set up Signal Generator SG-l/ARN to read 500
center sector on the panel. Tighten the knob set
microvolt at 114.9 mc and modulate it at 30 percent
screws carefully with the knob set in this position.
with the 9960 FM signal from Modulator MD-83A/ARN.
b. With the AUDIO SELECTOR still in the 90~ po-
b. Connect this signal into the navigation receiver
sition and the LOC-GS control set to the middle of the
and read the avc voltage with a d-c vacuum tube volt-
white center sector, adjust the 90~ LEVEL SET con-
meter. Also read the 30 cps voltage at the discrimi-
trol (figure 6- 11) to 20 percent modulation using the
nator with a Ballantine Model 300 electronic voltmeter.
procedure of paragraph 6-46.
c. Substitute Signal Generator SG-13/ARN for Signal
c. Connect the Ballantine Model 300 electronic volt-
Generator SG-l/ARN. Adjust SET LINE TO 2 IV,
meter to the AUDIO OUT connector and read the 90
METER ZERO, and CARRIER SET controls. With the
cps voltage.
AUDIO SELECTOR in the 9960 FM position adjust the
MICROVOLTS dial until the same receiver avc voltage
d. Without changing the setting of the LOC-GS con-
is obtained as in step b above.
trol, rotate the AUDIO SELECTOR to 150~ position
and adjust the 150~ LEVEL SET control (figure 6-11)
d. Adjust the 9960 FM DEV control to obtain the
to obtain the same voltage at the AUDIO OUT connec-
same discriminator voltage as was read in step b
tor as read in step a, above, for 90 cps.
above.
ADJUSTMENTS. The zero db adjustments in para-
QUENCY, 9960 FM FREQ, 9960 FM DEV, 30~ LEV-
graph 6-49 above must be made before the procedure
EL SET and 9960 FM LEVEL SET controls must be
below is undertaken.
adjusted before beginning the following procedure.
a. Connect an a-c vacuum tube voltmeter to the
a. This adjustment and the following VOR tracking
AUDIO OUT connector on Signal Generator SG-
adjustment require the use of Indicator ID-249A/ARN
13/ARN. Adjust SET LINE TO 2 lV, METER ZERO
and an accurate zero reading microammeter connec-
and CARRIER SET controls.
ted across the vertical (omni) crosspointer. (See fig-
ure 5-1. ) The AN/ARN-14 crosspointer output is de-
b. Loosen the two front panel screws that lock the
signed for a 333-ohm load. The Weston Model 901
two sectors on the LOC-GS control. Rotate the LOC-
microammeter has a 1000-ohm movement as do the
GS control to the right until the 90 cps voltage as read
ID-249A/ARN crosspointer movements. To obtain the
at the AUDIO OUT connector, with the AUDIO SELEC-
necessary 333-ohm load in this test setup, the glide
TOR on the 90~ position, is twice the 150 cps voltage
slope crosspointer must be paralleled with the omni-
as read at the same point with AUDIO SELECTOR on
crosspointer.
150~ position. When the setting of the LOC-GS con-
trol is obtained that gives a 2 to 1 ratio of voltages,
b. Set up Signal Generator SG-l/ARN to read 500
move the right hand sector until the top engraved line
microvolt at 114.9 mc and modulate it at 30 percent
on the sector is aligned with the center line on the
with the VOR signal from Modulator MD-83A/ARN.
knob. Hold the sector so it cannot move and turn the
Connect output of Signal Generator SG-l/ARN to input
knob aside and tighten the screw to lock the sector in
of the navigation receiver.
this position.
c. Set the PHASE ANGLE SELECTOR on Modulator
c. Use the same procedure to set the left hand sec-
MD-83A/ARN to 0 and adjust the SET control on In-
tor. At this position the 150 cps voltage must be
dicator ID-249A/ARN until the microammeter reads
twice the 90 cps voltage for the proper setting of the
zero (centered). Do not change this setting of the
sector. Use extreme care tn making these sector ad-
SET control. Read the receiver avc voltage with a
justments. The glide slope and phase localizer oper-
d-c vacuum tube voltmeter.
at ion depends upon these adjustments.
d. Substitute Signal Generator SG-13/ARN for Sig-
6-51. GLIDE SLOPE O DB AND 3 DB TO 3.75 DB
nal Generator SG-l/ARN and Modulator MD-83A/ARN.
ADJUSTMENTS. The glide slope is automatically ad-
Set MEGACYCLES dial to 114.9 mc and adjust CAR-
justed when the tone localizer adjustment is made. It
RIER SET control for red line indication.
