TM 11-6625-622-40
CHAPTER 2
FUNCTIONING OF EQUIPMENT
2-1. General
IN connector J4, to the DC POWER switch and circuit
breaker CB1. Circuit breaker CB1 is rated at 45 am-
The test unit (main component of Test Harness, Radio
Set AN/URM-157 or AN/URM-157A) is used in the test-
peres. When DC POWER circuit breaker CB1 is at ON,
ing and troubleshooting of Receiver-Transmitter,
dc is applied to 516H-1 connector J5 pin 23 and to
Radio RT-698/ARC-102. It has both alternating-current
618T-2-OFF-618T-3 switch S1. When switch S1 is at
(ac) and direct-current (dc) power distribution circuits.
618T-3, seven branches from switch S1, pins 11,8,5, and
2 conduct dc power, through 618T- 2/3 connector J1, pins
The control unit controls frequency, radiofrequency,
radiofrequency (rf) sensitivity, and mode of operation
1,13,2, 14, 3, 15, and 17, to the high-voltage power sup-
of the receiver-transmitter. The directional wattmeter
ply module of the receiver-transmitter under test. DC
provides for the measurement of foward and reflected
power, available at the input of S1, is connected
transmitter output power. The 50-ohm load is used as
through fuse F4 to connector J1, pins 4 and 16. Fuse F4
matched load for the receiver-transmitter. A dummy
is rated at 10 amperes, and protects the 27.5-volt dc con-
antenna is provided when a resistive-capacitive load is
trol circuitry of the receiver-transmitter. The 27.5 volts
needed. Audio jacks in the test unit can be used in place
dc is fed back to the test unit from the receiver-
of audio jacks in the receiver-transmitter.
transmitter, through connector J1 pin 56. One line con-
nects to ANT. CPLR connector J6, pins, r, s, and t;
2-2. Ac Distribution Circuit
another branch connects to KEY INTLK switch S7, pin
The 115-volt, 3-phase,400-Hertz(Hz) input poweris ap-
1, and another branch connects to J2 pin 56. If switch
plied to switch S3 of the test unit through AC IN con-
S7 is at BY PASS, 27.5 volts dc is connected to connec-
nector J7, 1 FUSE F1, 2 FUSE F2, and 3 FUSE
tor J6 pin X, and one branch is fed back to the receiver-
F3. The 1, 2, 3 fuses are rated at 5 amperes
transmitter key interlock circuit, through connector J1
each, and protect both the receiver-transmitter under
pin 5.
test and the test unit. When at ON, AC switch S3 ap-
plies power to 618T-2-OFF-618T-3 switch S1. When
2-4. Rf Load
switch S1 is at 618T-3 (center position OFF), phases 1
and 2 are open. (Three-phase power is not used by the
The 50-ohm resistive rf load is available at 50 RF
RT-698/ARC-102.) Phase 3 is fed around switch S1 to
LOAD connector J9 on the test unit top panel. The 50-
516H-1 connector J5 pin 16, where it is tied to 115 V, 400
ohm load is provided by a series-parallel connection of
CPS OUT outlet J18. Three-phase, 115-volt, 400-Hz ac
power is applied to the receiver transmitter under test
50-ohm resistors R1 through R4.
through 618T- 2/3 connector J1 pin 12. Ac power is
2-5. Resistive-Capacitive Load
returned from the receiver-transmitter, through con-
nector J1 pin 11 and through the test unit, to ANT.
A resistive-capacitive load is available between DUM-
CPLR connector J6 pin S, where it is applied to the an-
MY ANTENNA INPUT jack J15 and ground jack J16.
tenna coupler being used.
It consists of a parallel combination of 75-
2-3. Dc Distribution Circuit
micromicrofarad (f) capacitors C1 and C2 in series
The 27.5 volts dc is applied to the test unit, through DC
with the 50-ohm rf load.
Change 1 2-1
