Receiver Audio Output Checks - TM-11-6625-2609-120021

TM 11-6625-2609-12

(5) Slowly increase the AN/USM-44 out-

(3) Set the VHF COMM frequency selector

put level until the squelch opens as indicated by

switches to 132.500 MHz. An output indication

the presence of a tone in the headset. The AN/

should be obtained on the ME-30A/U.

USM-44 level should not be greater than 1 micro-

(4) Connect the ME-30A/U to the DATA

volt.

LINK OUTPUT jacks. The indicated voltage

( 6 ) S e t t h e A N/ U S- 4 4 o u t p u t l e v e l

should be considerably lower than that obtained

to less than .1 microvolt

in (3) above.

microvolt. Adjust the EXT. SQUELCH CON-

TROL fully counterclockwise. Slowly increase

b. Receiver Audio Output Checks. Start the

the AN/USM-44 output level until the squelch

equipment as instructed in paragraph 2-6 and

opens. The AN/USM-44 level should be approxi-

proceed as follows:

mately 50 microvolt. Actual break points are a

function of the AN/ARC-134 internal adjust-

(1) Leave the AN/USM-44 connected and

ments and are not dependent upon the main-

adjusted as described in a above, except set for

tenance kit.

30 percent modulation.

(2) Connect the H-157/AIC to the U-94A/

d. Channel Selection Checks. Start the equip-

U connector.

ment as instructed in paragraph 2-6 and proceed

as follows:

(3) Set the AUDIO switch to ON. A signal

should be heard in the headset.

(1) Leave the AN/USM-44 connected and

adjusted as described in a above. Leave the head-

(4) Set RECEIVERS switch 3 to OFF. The

set connected as described in b above.

signal heard in the headset should disappear. In

sequence; set RECEIVERS switches 1, 2, 4, INT,

(2) Set the AUDIO switch to ON.

and NAV to ON. No signal should be heard in

(3) Set the EXTERNAL SQUELCH switch

the headset. Return RECEIVERS switches 1, 2,

to OFF. Adjust the AN/USM-44 output atten-

4, INT, and NAV to the OFF position. Return

uator for a 5-microvolt output.

RECEIVERS switch 3 to the ON position. The

(4) Set the AN/USM-44 and the radio con-

signal should again be heard in the headset.

trol VHF COMM frequency selector switches to

(5) Set the EXTERNAL SQUELCH switch

each of the following frequencies and check for

to ON, and adjust the EXT. SQUELCH CON-

proper frequency selection as denoted by a tone

TROL until the signal just disappears.

in the headset: 116.00 MHz, 126.00 MHz, 136.00

(6) Press the radio control COMM TEST

MHz, 146.00 MHz, 147.00 MHz, 148.00 MHz,

switch. The signal should be heard again in the

149.00 MHz, 140.00 MHz, 141.00 MHz, 142.00

headset, indicating that the AN/ARC-134 squelch

MHz, 143.00 MHz, 144.00 MHz, 145.00 MHz,

circuit is disabled. Release the COMM TEST

145.10 MHz, 145.20 MHz, 145.30 MHz, 145.40

switch.

MHz, 145.50 MHz, 145.60 MHz, 145.70 MHz,

145.80 MHz, 145.90 MHz, and 145.95 MHz.

( 7 ) Set the SQUELCH DISABLE switch

( 5 ) Disconnect the AN/USM-44 and the

to ON. Indications should be the same as in (6)

ME-30A/U from the maintenance kit.

above.

( 8 ) Set the SQUELCH DISABLE switch

e. Transmitter Output and Control Circuit

to OFF.

C h e c k s . Start the equipment as instructed in

paragraph 2-6 and proceed as follows:

c. Squelch Control Circuit Checks. Start

the

(1) Connect Wattmeter, Radio Frequency

equipment as instructed in paragraph 2-6

and

AN/URM-120 and Dummy Load DA-75U to an-

proceed as follows:

tenna connector W1P3 on the maintenance kit

(1) Leave the equipment connected as

de-

(fig. 2-4).

scribed in a and b above.

(2) Set the VHF COMM frequency selec-

(2) Leave switches in positions set at

the

tor switches (fig. 2-1) to 132.500 MHz.

conclusion of b above.

(3) Set the test panel PTT switch to ON.

( 3 ) Adjust EXT. SQUELCH CONTROL

A power output indication should be observed

fully clockwise.

o n the AN/URM-120, the INPUT CURRENT

(4) Adjust the AN/USM-44 output atten-

meter should indicate between 6 and 9 amperes,

uator for a minimum output (less than .1

and the red PTT lamp should light.

microvolt).

2-5

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