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Frequency divider
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Transmitter up-converter
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Receiver down-converter
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RF splitter
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Three modulator/demodulators (modems)
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ARINC 429 interface
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Conference Europeenne des Administrations des Postes et des Telecommunications (CEPT) interface
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Microprocessor
*
Front panel.
Transmit Operations
The RFU gets transmitted RF signals from the SDU. A filter sends the 2016 MHz reference frequency to a divider to make the 10.08 MHz base reference frequency for the RFU. It uses the
10.08 MHz reference frequency for transmit and receive operations.
EFFECTIVITY
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The 2016 MHz filter sends the RF input to a mixer in the RFU.
The RFU gets digital passenger telephone data on the CEPT interface. It may also get digital audio from the SDU.
The microprocessor sends the digital data to the modems. If all three modems are in use and the RFU needs another channel, it sends digital audio/data to the SDU for it to change to RF.
Each modem changes the digital data from the microprocessor to an intermediate frequency (IF) and sends it to the transmitter up-converter.
The transmitter up-converter changes the IF signals from the modems to RF and sends them to the mixer.
The mixer gets the RF outputs from the SDU and the transmitter up-converter and puts them on one RF output. The mixer output goes to the RF attenuator and then to the RF splitter.
Receive Operations
The RFU gets received RF inputs from an antenna system through the RF combiner (RFC). An RF splitter sends the input signals to the receiver down-converter. It also sends the RF to the SDU for flight deck audio and PAX TEL if necessary.
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SATCOM SYSTEM -RADIO FREQUENCY UNIT FUNCTIONAL DESCRIPTION
The receiver down-converter changes as many as three channels of RF signals to intermediate frequencies and sends them to the modems.
Each modem changes its IF input to digital data and sends it to the microprocessor.
The microprocessor uses part of the data from the modem to find where the data needs to go. It sends CEPT data to the passenger telephone system and digital audio/data to the SDU for the flight deck.
Control Signals
The RFU gets signals from the SDU through the ARINC 429 interface. The signals from the SDU control the RFU operations. The SDU may also send BITE commands to the RFU during system test. The RFU sends BITE data and status to the SDU.
The microprocessor may get a test signal from the front panel switch. This starts a test of only the RFU. The microprocessor sends status signals to the front panel lights.
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SATCOM SYSTEM -BEAM STEERING UNIT AND HIGH POWER RELAY FUNCTIONAL DESCRIPTION
General
There is a beam steering unit (BSU) for each high gain antenna. The BSUs receive digital beam steering signals from the satellite data unit (SDU). They use these signals to make a narrow beam to the satellite.
The BSUs change beam steering signals into phase shift data. This data changes the angle of the signals sent to specific antenna elements. The antenna elements make a narrow beam that points at the satellite.
The BSU has these components:
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Three power divider/combiners
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Twenty phase-shifters
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Processor -I/O module.
The high power relay (HPR) sends the RF from the high power amplifier (HPA) to the active LNA/DIP. The port BSU controls the HPR.
This functional description is for the port BSU. The starboard BSU is similar.
BSU Power Dividers/Combiners
The power divider/combiners divide the transmit RF input of the BSU to each of 20 phase shifters. They also collect received RF input from the phase shifters and combine them into a single output to the low noise amplifier/diplexer (LNA/DIP).
BSU Phase Shifters
The phase shifters change the phase of each RF signal sent to the high gain antenna (HGA) elements.
BSU Processor -I/O Module
The processor -I/O module has these functions:
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Receives satellite positions and other data from the SDU and sends BITE status to SDU
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Sends BITE status to the other BSU and receives BITE status from the other BSU
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Sends a mute signal to the class A HPA
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