Use Fold-Out 12 to locate each item on the order wire.
Control or Indicator
POWER lamp (green) -------------------------- Indicates unit is receiving
CALL lamp (red) ------------------------------- Indicates an incoming call.
RING pushbutton switch-----------------------Lights CALL lamp and activates
buzzer at distant stations
e. Order Wire Patch-Thru Switch. When two AN/GRC-103's are used at a repeater site,
a patch-thru of the order wire is necessary. This is accomplished by switching the FDM/PCM
switch to PCM. Access to the switch is gained by loosening the four screws on the front of the
order wire case. After the front panel is withdrawn, the switch can be found on a printed circuit
board in the left-hand compartment of the order wire case.
f. Buzzer Silencing. The alarm functions on the transmitter or receiver operate
whenever they change state. This means when the alarm lamps light or go out the buzzer will
sound. Under normal operating conditions the BUZZER OFF pushbuttons are used to silence
the buzzers. In forward area operations it may be necessary to silence the buzzers and dim the
alarm lamps. This is accomplished by means of BUZ OFF/ALM NOR switches inside the
transmitter and receiver fixed heads and the order wire unit. The switches in the fixed head may
be reached by first loosening the four screws holding the units in their cases and withdrawing the
units 3 or 4 inches. Locate the switches in the front upper corner on the right-hand side of the
transmitter fixed head and in the front upper corner on the left-hand side of the receiver fixed
head. Access to the order wire switch is gained by loosening the four screws on the front panel
and withdrawing the front panel. The switch is mounted on a printed circuit board in the left-
hand compartment of the order wire case.
Thus far in this lesson you have learned two methods of connecting the components of Radio Set
AN/GRC-103. One connection arranged the radio set as a 12-channel PCM radio terminal and
the other set up a 12-channel PCM radio repeater. You also learned that the AN/GRC-103 has
three basic functions; signal transmission, signal reception, and an order wire. In addition you
now know the location and purpose of each control and indicator located on each component of
the radio set.
You are now familiar with the location and function of each control and indicator on the
AN/GRC-103. Continue to Lesson Exercise 2.