VHF SYSTEM -MAIN EQUIPMENT CENTER COMPONENT LOCATIONS
VHF Component Locations
The VHF communication transceivers are in the main equipment center.
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VHF SYSTEM -MAIN EQUIPMENT CENTER COMPONENT LOCATIONS
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VHF SYSTEM -EXTERNAL COMPONENT LOCATIONS
VHF Component Locations
The three VHF antennas are on the upper and lower fuselage. The left and center antennas are on the upper fuselage. The right antenna is on the lower fuselage.
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VHF SYSTEM -EXTERNAL COMPONENT LOCATIONS
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VHF SYSTEM -POWER INTERFACE
General
The captain’s flight instrument bus sends 28 VDC to:
*
The left VHF communication transceiver
*
The left radio tuning panel (RTP). The left main dc bus sends 28 VDC to:
*
The center VHF communication transceiver
*
The center RTP. The right main dc bus sends 28 VDC to:
*
The right VHF communication transceiver
*
The right RTP.
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777 AIRCRAFT MAINTENANCE MANUAL
VHF SYSTEM -POWER INTERFACE
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VHF SYSTEM -TUNING INTERFACE
General
The VHF communication system uses data buses to share tuning information between the radio tuning panels (RTPs), the VHF communication transceivers, and the airplane information management system (AIMS) cabinets.
Tuning Buses
The RTPs send tuning data to the VHF communication transceivers. Any RTP can tune any transceiver.
Each RTP has these two ARINC 429 output buses:
*
Tuning bus
*
Crosstalk bus.
Both the left and right RTPs send tuning data to all three transceivers and to the left and right AIMS cabinets.
The center RTP sends tuning data to the left and right RTPs and to the left and right AIMS cabinets.
Both the left and right AIMS cabinets send auto-tune data to all three RTPs.
Port Select Discrete
The left RTP sends a port select discrete to the left and center transceivers. The right RTP sends a port select discrete to the right transceiver.
Each transceiver has two tuning data input ports; port A and port B. The transceiver uses the port select discrete to select its input port. A grounded port select discrete causes the transceiver to use port A. An open port select discrete causes the transceiver to use port B.
Crosstalk Buses
Each RTP sends tuning data to the other RTPs on crosstalk buses. This keeps the RTP tuning data synchronized and permits any RTP to tune any transceiver.
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777 AIRCRAFT MAINTENANCE MANUAL
VHF SYSTEM -TUNING INTERFACE
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VHF SYSTEM -VOICE RECEIVE/TRANSMIT INTERFACES
General
You use an audio control panel (ACP) to select a VHF communication transceiver for voice communication. You also use a radio tuning panel (RTP) to select a frequency for the transceiver. Any push to talk (PTT) signal activates the selected transceiver.
Signal Flow -Receive
The VHF communication antennas receive RF signals and send them to the transceivers. The transceivers change the RF signals to audio signals and send them to the audio management unit (AMU). The AMU sends the audio signals to the headsets and speakers.
The transceiver sends received audio to the SELCAL decoder to monitor for selective call tones.
Signal Flow -Transmit
The AMU sends the mic audio and the mic switches signal to the selected transceiver. The transceiver changes the mic audio to an RF signal and sends it to the VHF antenna. The VHF antenna transmits the RF signal.
The transceiver sends key event (PTT) to the AIMS digital flight data acquisition function (DFDAF).
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