The satellite communications (SATCOM) system supplies voice and data channels for global communication through satellites.

The SDU is the primary component of the SATCOM system. It supplies the interfaces to other aircraft systems and reads the configuration pins that identify the SATCOM configuration for the aircraft. This helps the SDU control system operation.

The SDU keeps an owner's requirement table (ORT) that contains the system parameters for the aircraft in which the SATCOM system is installed. The SDU must have an ORT installed for proper system operation. The SDU also keeps a list of all ground stations. The SDU uses the list to make the selection of a ground station. It can only transmit through one satellite to one ground station at a time.

The SDU contains the global position of each network satellite. The SDU uses this data, plus navigation coordinates from the inertial reference system, to calculate the aircraft position in relation to the satellite. The SDU then sends pointing and tracking coordinates to the antenna control unit to position the antenna in the direction of the satellite. The SDU adjusts the pointing and tracking coordinates as necessary to make sure that the antenna is always pointed at the satellite.

During transmission, the SDU digitizes the voice and data signals and modulates this base band data with an RF carrier frequency. The RF signal is then sent to the HPA through the RFU. The HPA amplifies the RF signal to a power level necessary for satellite transmission. The HPA then sends the RF signal to the HGA through the D/LNA.

During reception, the SDU receives the RF signal from the D/LNA through the RFU. The SDU demodulates the RF carrier frequency in the RF signal to supply the baseband data. If the RF signal has a voice component, the SDU changes the baseband data into a digital signal for the cabin communication system (CCS).

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The satellite data unit (SDU) is installed on a mounting tray in the main avionics compartment. Two hold-down clamps hold the unit in position. A fan on the mounting tray keeps the unit in a safe temperature range. The SDU weighs approximately 25.5 lbs (11.5 kg) and operates from +28 VDC aircraft power. A rear-mounted connector engages a mating connector in the mounting tray when the SDU is installed. The rear connector connects the SDU to other units in the SATCOM system, and to other aircraft avionics systems.

A 20-digit alphanumeric display on the front panel shows BITE failure indications. The alphanumeric display also shows the part numbers and MOD letters of the SDU, RFU, and HPA.

The SDU front panel also has two pushbuttons. One pushbutton is the SDU TEST switch. The other pushbutton is the CM/SCROLL switch. When you push the SDU TEST switch, the SDU initially does an internal BITE test. At the end of its internal self-test, the SDU starts a BITE test on the other system units. Each LRU then sends its BITE test result to the SDU. The SDU stores the BITE results in non-volatile memory and shows BITE failure indications on the alphanumeric display. When you push the CM/SCROLL switch, you can scroll through the BITE indications on the alphanumeric display and identify the defective LRU.

Two red lamps on the front panel show the BITE status for the SDU and other system units. The SDU FAIL lamp comes on if a failure occurs during the SDU internal BITE test. The SYSTEM LRU-FAIL lamp comes on if a malfunction occurs in any system LRU other than the SDU during the system-wide BITE test. A connector on the front panel makes data loads possible between a portable data loader and the SDU.

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The high power amplifier (HPA) is installed in an electromagnetic interference (EMI) enclosure in the empennage. Two hold-down clamps hold the unit in position. A fan in the aft equipment compartment connects to the mounting tray with a duct to extract heat from the unit. The HPA weighs approximately 29 lbs (13 kg) and operates from +28 VDC aircraft power. A rear-mounted connector engages a mating connector in the mounting tray when the HPA is installed. The rear connector connects the HPA to other units in the SATCOM system.

The front panel has a push-to-test switch, a red (FAIL) lamp, and a green (PASS) lamp. When you push the push-to-test switch, it starts an internal BITE test for the HPA. The red lamp comes on if a malfunction occurs during the BITE test. The green lamp comes on if the unit completes its BITE test without a malfunction. A connector on the front panel makes data loads possible between a portable data loader and the HPA.

The HPA amplifies the RF signals to a power level necessary for satellite transmission. The SDU controls the HPA through an ARINC 429 data bus interface. The HPA sends transmission power data to the SDU on the ARINC 429 data bus. The SDU uses this data to control the number of calls that the SATCOM system can make at anyone time. The HPA also sends maintenance data and indications of system malfunctions, such as temperature warnings or power supply malfunctions, to the SDU.

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The high gain antenna (HGA) is installed on top of the vertical stabilizer. Eight bolts hold the unit in position. The HGA weighs approximately 5.7 lbs (2.5 kg) and operates from 5 VDC power supplied by ACU.

The HGA contains an antenna and two electrical motors. The antenna is installed on a shaft that turns in a yoke. The motors move the antenna in a direction from 5 to 90 degrees in elevation and 360 degrees in azimuth. One motor supplies pitch movement and the other motor supplies roll movement to point the antenna at the satellite. Internal sensors in the HGA send antenna position data to the ACU.

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The diplexer/low noise amplifier (D/LNA) is installed on top of the vertical stabilizer near the HGA. Four bolts hold the unit in position. The D/LNA weighs approximately 6 lbs (2.7 kg) and operates from 25 VDC power supplied by the ACU.

The D/LNA supplies the interface between the SATCOM system avionics and the antenna. The D/LNA puts together the receive and transmit RF signals on a single signal path for the antenna. In the transmit path, the D/LNA connects to the HPA and filters the transmit RF signals for noise and unwanted signals. In the receive path, the D/LNA filters received RF signals from the antenna to prevent non-linear operation of the SATCOM system. The D/LNA amplifies receive RF signals to a level that the SATCOM system can use. The amplified RF signals are then sent to the RFU.

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The antenna control unit (ACU) is installed on top of the vertical stabilizer adjacent to the HGA. Four bolts hold the unit in position. The ACU weighs approximately 7.4 lbs (3.3 kg) and operates from +28 VDC aircraft power. No special cooling system is necessary for the ACU.

The ACU supplies the interface between the SDU and the HGA. As the aircraft moves in relation to the satellite, the SDU continuously calculates new pointing and tracking coordinates for the antenna. The ACU receives these coordinates from the SDU on an ARINC 429 databus. The ACU changes these coordinates into antenna motor pitch and roll drive signals. These drive signals make the motors position the antenna in the direction of the satellite.

The ACU receives D/LNA control signals from the SDU on the sameARINC 429 data bus. The ACU changes these control signals into signals applicable for the discrete interface lines between the ACU and the D/LNA. The ACU does a BITE test of itself, the antenna, and the D/LNA when power is first applied or during a SATCOM system BITE test. The ACU sends the BITE test results to the SDU on an ARINC 429 data bus. The ACU also supplies the interface to the aircraft primary power supply for the D/LNA and antenna.

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The RFU is installed on a mounting tray in the main avionics compartment. Two hold-down clamps hold the unit in position. A fan on the mounting tray keeps the unit in a safe temperature range. The RFU weighs approximately 19 lbs (8.5 kg) and operates from +28 VDC aircraft power. A rear-mounted connector engages a mating connector in the mounting tray when the RFU is installed. The rear connector connects the RFU to other units in the SATCOM system.

The front panel has a push-to-test switch, a red (FAIL) lamp, and a green (PASS) lamp. When you push the push-to-test switch, it starts an internal BITE test for the RFU. The red lamp comes on if a malfunction occurs during the BITE test. The green lamp comes on when the RFU completes its BITE test without a malfunction. A connector on the front panel makes data loads possible between a portable data loader and the RFU.

The RFU supplies three full-duplex voice communication channels when it operates together with the SDU. The channels transmit and receive digital voice signals to and from the cabin communication system through a CEPT E1 interface with the SDU.

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The RF attenuator is installed behind the RFU in the avionics compartment. The RF attenuator connects in the RF TX line between the SDU and the HPA. It keeps RF line losses down to the specified operation parameters.

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For the operation of the aircraft-satellite communications system (SATCOM), three parts are necessary:

• SATCOM system, referred to as the aircraft earth station (AES)
• Ground earth station (GES)
• Communications satellite

The SATCOM is a worldwide mobile avionics communications system that supplies continuous voice and data communications services to and from the aircraft via satellites. The SATCOM system uses the four geo-stationary Inmarsat satellites to supply nearly the worldwide communications coverage, except in areas near the North and South poles.

The SATCOM system, together with the cabin communication system of telephones and faxes/PCs, and other aircraft avionics, make it an aircraft earth station (AES). The standard interfaces between the SATCOM system and other aircraft avionics give the AES the ability to accept data and voice messages from different sources. The AES encodes and modulates this information onto applicable RF carrier frequencies for transmission to the satellite, and from the satellite to the GES. The AES also receives the RF signals from the GES via the satellite, demodulates them and decodes the encoded messages,then sends the data or voice message for use by the passengers or flight crew.

The SATCOM system connects with an antenna subsystem to supply six communication channels. Five channels supply voice communication and optional Personal Computer (PC) data and fax communication for the passengers and flight crew. One channel is a digital data channel that supplies two functions:

• Communication control between the AES, GES, and satellite
• An interface with the airborne data link system to transmit and receive the ACARS data

System components that are used as part of the AES include:

• Cabin communications
• Inertial Reference System (IRS)
• Airborne Data Link System (ADLS)
• Maintenance system
• FAX/PC

The cabin communications supplies a SATCOM interface to the flight compartment and cabin via the use of handsets. The IRS interfaces to the SATCOM as the primary and secondary sources for aircraft orientation. The ADLS interface supplies the data link, weather, and other ACARS-type data.

If any part of the SATCOM system is not functional, or if the satellite communication is not available, a SAT NOCOMM advisory will be displayed on the FMS control display unit (CDU).

Note:
For maintenance purposes, the aircraft must be in on open area outside the hanger to get direct view of the satellite to have SATCOM system operational.

The advisory messages in the table that follows are related to the SATCOM system. These advisory messages are shown in the lower right-hand corner of the FMS CDU display, next to the bottom right-hand line select key and, above the scratchpad area. When there are more than one advisory messages present at the same time, only the ones with the highest priority are displayed. Once the highest priority message is cleared, the next priority advisory message is displayed.

ADVISORY	DESCRIPTION
NOCOMM	SET: When none of the three air/ground links are available CLEARED: When any communication link becomes available
SAT NOCOMM	SET: when SATCOM is configured and not available CLEARED: When SATCOM becomes available

ADVISORY	DESCRIPTION
TEL NOCOMM	SET: When telephony is configured and not available CLEARED: When telephony becomes available

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The SATCOM system has the following built-in test equipment (BITE) modes:

Power-On Self-Test (POST)

The POST is an internal test program that does a functional test of the SATCOM system. Each line replaceable unit (LRU) in the system automatically does its own POST when power is initially applied. An individual LRU that satisfactorily completes the POST is serviceable.

Pilot-Activated Self-Test (PAST)

The PAST does the same internal test of an individual LRU as POST. The PAST starts when you push a switch on the front panel of an LRU. The LRU is serviceable if it completes the PAST without a failure indication.

Continuous Monitoring

This mode continuously monitors the BITE of an LRU during usual system operation. Continuous monitoring is an auxiliary program task that has no effect on system operation.

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Component Location Index
IDENT	DESCRIPTION	LOCATION	IPC REF
A228	SATELLITE DATA UNIT	ZONE(S) 142	23-13-01 [ GX ] [ GXRS ] [ G5000 ]
A709	SATELLITE RECEIVER/TRANSMITTER (SRT)	ZONE(S) 312	23-13-03 [ GX ] [ GXRS ] [ G5000 ]
A229	HIGH POWER AMPLIFIER	ZONE(S) 345	23-13-05 [ GX ] [ GXRS ] [ G5000 ]
A713	SPLITTER	ZONE(S) 346	23-13-07 [ GX ] [ GXRS ] [ G5000 ]
A710	HIGH SPEED TRANSCEIVER (HST 1)	ZONE(S) 312	23-13-10 [ GX ] [ GXRS ] [ G5000 ]
A711	HIGH SPEED TRANSCEIVER (HST 2)	ZONE(S) 312	23-13-10 [ GX ] [ GXRS ] [ G5000 ]
E57	HIGH GAIN ANTENNA	ZONE(S) 346	23-13-13 [ GX ] [ GXRS ] [ G5000 ]
E506	HIGH GAIN ANTENNA	ZONE(S) 346	23-13-13 [ GX  ][ GXRS ] [ G5000 ]
A712	COMBINER	ZONE(S) 312	23-13-14 [ GX ] [ GXRS ] [ G5000 ]
A230	DIPLEXER/LOW NOISE AMPLIFIER	ZONE(S) 346	23-13-17 [ GX ] [ GXRS ] [ G5000 ]
A722	DIPLEXER/LOW NOISE AMPLIFIER	ZONE(S) 346	23-13-17 [ GX ] [ GXRS ] [ G5000 ]
A227	ANTENNA CONTROL UNIT	ZONE(S) 346	23-13-21 [ GX ] [ GXRS ] [ G5000 ]
A723	ANTENNA CONTROL UNIT	ZONE(S) 346	23-13-21 [ GX ] [ GXRS ] [ G5000 ]
A240	RADIO FREQUENCY UNIT	ZONE(S) 142	23-13-25 [ GX ] [ GXRS ] [ G5000 ]
A231	RF ATTENUATOR	ZONE(S) 142	23-13-29 [ GX ] [ GXRS ] [ G5000 ]
HS506	JET PHONE	ZONE(S) 221/222	23-13-32 [ GX ] [ GXRS ] [ G5000 ]

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