SATCOM SYSTEM -VOICE AND DATA TRANSMIT/RECEIVE INTERFACES
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SATCOM SYSTEM -CONTROL AND STATUS INTERFACES
General
The satellite data unit (SDU) supplies control and failure data for the SATCOM system.
These components have an interface with the SDU for control and status data:
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High power amplifiers (HPAs)
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Low noise amplifier/diplexers (LNA/DIPs)
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Beam steering units (BSUs)
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Airplane information management system (AIMS)
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Control display units (CDUs)
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Radio frequency unit (RFU).
High Power Amplifiers
The high power amplifiers (HPAs) receive control signals from the SDU. The HPAs receive the control signals to adjust the output of their transmit signals. The HPAs send BITE data to the SDU. The class A HPA receives a mute signal from the BSUs to shut down the HPA when the system switches outputs from one antenna to the other.
Low Noise Amplifier/Diplexer
The low noise amplifier/diplexer (LNA/DIP) for the low gain antenna (LGA) receives on/off signals from the SDU. The LNA/ DIP sends BITE data to the SDU. The LNA/DIPs for the high gain antennas send BITE data to the beam steering units (BSUs).
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Beam Steering Units
The BSUs receive direction signals from the SDU. The BSUs send BITE data to the SDU. Each BSU also sends BITE data to the other BSU. The BSUs send on/off signals to the LNA/DIPs. The BSUs also send a mute signal to the HPA. The port BSU also sends control signals to the high power relay (HPR).
Airplane Information Management System (AIMS)
The central maintenance computing function (CMCF) in the airplane information management system (AIMS) receives SATCOM system BITE data from the SDU.
AIMS sends this data to the SDU:
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International Civil Aviation Organization (ICAO) address
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Inertial reference data
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Software for system configuration
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Data load enable
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BITE commands.
Radio Frequency Unit
The radio frequency unit (RFU) receives frequency selection data from the SDU. Each satellite operates on a different frequency to decrease interference from other satellite signals.
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SATCOM SYSTEM -CONTROL AND STATUS INTERFACES
Audio Management Unit
The audio management unit (AMU) sends PTT signals to the SDU. The SDU sends call light signals to the AMU.
Control Display Units
The flight crew uses the control display units (CDUs) to send control signals to the SDU for SATCOM system operation.
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SATCOM SYSTEM -CONTROL AND STATUS INTERFACES
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SATCOM SYSTEM -SATELLITE DATA UNIT
Purpose
The satellite data unit (SDU) is the system interface and controller for the SATCOM system. It contains system operation software. The SDU also contains position and frequency data for each satellite.
Physical Description
The SDU is a 6 MCU LRU and weighs 24 pounds. It has these front panel controls and indicators:
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SDU FAIL -shows red if the SDU has a failure
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SDU TEST switch -push this switch to start a test of the SDU
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System status display -shows data related to the the pass or fail status of SATCOM LRUs
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CM/SCROLL -push this button to scroll through messages on the system status display
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SYSTEM LRU-FAIL -shows red if any other SATCOM LRU has a failure.
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777 AIRCRAFT MAINTENANCE MANUAL
SATCOM SYSTEM -SATELLITE DATA UNIT
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SATCOM SYSTEM -RADIO FREQUENCY UNIT
Purpose
The radio frequency unit (RFU) changes digital audio from the cabin telecommunications unit (CTU) to radio frequency signals. The RF signal is mixed with the RF signal from the satellite data unit (SDU). The mixed RF is sent through the RF attenuator to the high power amplifier.
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