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 TM 11-5895-1847-12&P
OPERATOR AND UNIT MAINTENANCE
LCU 2000 GLOBAL MARITIME DISTRESS AND SAFETY SYSTEM
THEORY OF OPERATION
INMARSAT-C SATELLITE COMMUNICATIONS SYSTEM OPERATION
The INMARSAT-C satellite communications system is comprised of an INMARSAT-C transceiver, data terminal,
parallel printer and INMARSAT-C antenna. The INMARSAT-C transceiver, located in the GMDSS 9701 console,
receives and transmits a radio signal to a geosynchronous orbiting satellite allowing distress, e-mail, FAX and
TELEX communications. The transceiver is cabled to the INMARSAT-C antenna located on the yardarm. E-mail,
FAX and TELEX messages are sent using the data terminal. An auto switch routes the received messages to the
parallel printer to be printed or viewed by the data terminal. In an emergency situation, a distress may be transmitted
from the transceiver. The current ship's position is transferred from the communications Precision Lightweight
Global Positioning Receiver (PLGR) through the communications interface and switchbox to the INMARSAT-C.
The INMARSAT-C is powered by ship's power through the 9701 console. In the event of an AC system failure,
backup power to operate the INMARSAT-C is received from the GMDSS emergency batteries.
COMMUNICATIONS AN/PSN-11(V)1 PLGR
The communications PLGR receives ship's position data through the communications PLGR antenna from Global
Positioning System (GPS) satellites. The PLGR is powered by ship's power through the communications interface
and switchbox and PLGR interface cable. The communications PLGR supplies current position information, through
the interface and switchbox and PLGR interface cable, to the INMARSAT-C transceiver, Digital Selective Calling
(DSC) controller and the DSC VHF/FM transceiver. The PLGR may be programmed for crypto operations using the
KYK-13 or KOI-18 crypto key.
COMMUNICATIONS INTERFACE AND SWITCHBOX
The communications interface and switchbox provides isolated and regulated ship's power to the communications
PLGR. The interface and switchbox acts as an interface to provide position data from the communications PLGR to
the INMARSAT-C transceiver, DSC controller and the DSC VHF/FM transceiver. Switches are located on the
interface and switchbox to either turn the position data signal off or on to each component. The communications
PLGR may be programmed by the INMARSAT-C data terminal using the data terminal interface on the interface and
switchbox with the appropriate cable.
GLOBAL MARITIME DISTRESS AND SAFETY SYSTEM (GMDSS) POWER
The GMDSS communications system is powered by ship's power. The INMARSAT-C transceiver, watch receiver,
DSC controller and communications PLGR are supplied with power by a redundant power system through the
9701 console. The primary source of power for these components is the GMDSS power supply. The GMDSS power
supply converts 115 vac to a nominal 13.8 vdc. The GMDSS power supply receives power from the EP103 circuit
box using circuit breaker 3. In the event that alternating current is not available, the automatic power switch relay
automatically switches to receive power from the ship's GMDSS emergency batteries. The GMDSS DC converter
converts 24 vdc emergency battery power to a nominal 13.8 vdc to power the equipment. The satellite
communications system data terminal, parallel printer and DSC serial printer are powered by 115 vac from the
EP103 circuit box using circuit breaker 8. In the event of a main buss AC system failure, the data terminal, parallel
printer and DSC serial printer are powered by the emergency generator. No battery backup power capability exists for
these components.
DSC WATCH RECEIVER
The DSC watch receiver monitors preset frequencies for distress messages and alerts the operator through an audible
signal and visual signal. The watch receiver antenna is cabled to the watch receiver to provide the required radio
signal. The watch receiver is powered by ship's power through the GMDSS 9701 console.
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