Figure 1-8.-C-11950/ARC-187 control box.
Transmit Mode
In the transmit mode, the VHF XMTR control signal
from any one of the four ICS master control panels
applies a ground to the transceiver as the VHF key
signal. This VHF key signal provides the push-to-talk
command to the transceiver to switch it from the receive
to the transmit mode of operation. The synthesizer
generates transmitter drive frequencies from 116.000 to
155.975 MHz in 25 kHz steps. Audio from any of the
four ICS master control boxes are applied to the
modulator circuit. The modulator circuit provides
90-percent amplitude modulation. The compressor and
limiter circuits are included to prevent over-modulation.
The transmitter uses five stages of amplifiers to raise the
output to 20 watts. The RF output is routed to the
antenna, through the filter, for radiation. The transceiver
also produces a sidetone output, which is provided to the
ICS system in the same manner as the receiver audio.
UHF COMMUNICATIONS
Learning Objective: Recognize components
and operating principles of the UHF radio
system.
The AN/ARC-187 UHF radio system consists of the
UHF-1 radio set, UHF-2 radio set, and the interfacing
equipment. The UHF communication system provides
amplitude modulation, frequency modulation, and
frequency shift key (FSK) operations. The frequency
range of this radio system is 225.000 to 399.975 MHz.
MAJOR COMPONENTS
Each radio set in the system consists of an
RT-1571/ARC-187 receiver transmitter, a C-11950(V)3/
ARC-187 radio control, an AT-879/ARC antenna, and a
740645 antenna switching relay. The UHF-2 radio set
also contains a 974924 antenna select panel. The
antenna and the antenna switching relay will not be
discussed in detail in this manual.
RT-1571/ARC-187 Receiver Transmitter
The RT-1571/ARC-187 receiver transmitter
contains all the circuitry for the normal operation of the
UHF radio set.
C-11950/ARC-187 Radio Control Box
The C-11950/ARC-187 control box (fig. 1-8)
provides all the controls for normal operation of the
radio set. We will be discussing each of the controls and
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