in  progress  discrete  to  the  transceiver.  This  prevents 
transmission  and  reception d uring tuning  and  puts  the 
transceiver in tune mode. 

The PTT signal goes to the airplane information management system (AIMS) digital flight data acquisition function (DFDAF).
Signal Flow -Receive
The HF antenna receives RF signals and sends them to both HF antenna couplers. The antenna couplers send the RF signals to the HF communication transceivers. The transceivers change the RF signals to audio signals. The transceivers send the audio signals to the audio management unit (AMU).
The flight crew selects a receiver control switch on their ACP. The AMU sends the received audio to the flight crew stations.
The transceivers send received audio to the SELCAL decoder. The SELCAL decoder monitors the audio for an incoming call. It alerts the flight crew when the airplane receives a call.
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777 AIRCRAFT MAINTENANCE MANUAL

HF SYSTEM -RECEIVE/TRANSMIT INTERFACES

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HF SYSTEM -AIMS FAULT REPORTING AND TESTING INTERFACES

General
The HF system sends fault information to the AIMS cabinets from three sources:
*
HF communication transceivers

*
HF antenna couplers

*
Radio tuning panels (RTPs).

Transceiver and Antenna Coupler Interfaces
The HF communication transceivers send real time fault and status information to the AIMS cabinets. The fault information includes faults generated by the antenna couplers and the transceivers.
The air/ground relays send air/ground signals to the transceivers. The tranceivers use these signals to keep flight leg faults in memory.
The left AIMS central maintenance computing function (CMCF) tests the HF transceivers during ground tests. The CMCF sends test requests to the HF transceivers. The HF transceivers give the test results to the CMCF. The right AIMS cabinet gives test information, if the left AIMS cabinet fails.
Radio Tuning Panel (RTP) Interfaces
Each RTP sends HF system fault/status information to both AIMS cabinets.
AIMS sends HF system fault/status to the RTPs.

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HF SYSTEM -AIMS FAULT REPORTING AND TESTING INTERFACES

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HF SYSTEM -HF COMMUNICATION TRANSCEIVER

Purpose
The HF communication transceiver changes RF signals to audio signals during receive operation, and changes audio signals to RF signals during transmit operation. The transceiver amplifies RF transmit signals.
Physical Description
The HF transceiver has these features:
*
One KHz channel spacing

*
A frequency range of 2.000 MHz to 29.999 MHz

*
Maximum RF output power of 400 watts peak envelope power (USB), 125 watts (AM).

Operation -Controls and Indications
These are the three LED indicators and one push-button on the transceiver front panel:
*
LRU FAIL indicator -comes on for a transceiver fault

*
KEY INTERLOCK indicator -comes on for an antenna
coupler fault

*
CONTROL INPUT FAIL indicator -comes on for an RTP
tuning fault

*
SQL/LAMP TEST switch -HF system squelch disables and all LEDs come on.

The LED indicators come on to show failures.
The headphone and microphone jacks permit operation of the HF transceiver from the E6 rack in the aft cargo compartment.
Functional Description
The HF communication transceiver operates as a receiver/ transmitter in the amplitude modulation (AM) or upper side band (USB) modes. The transceiver detects the voice audio from the carrier frequency during reception, and modulates the voice audio during transmission.
An internal blower cools the transmitter.
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777 AIRCRAFT MAINTENANCE MANUAL

HF SYSTEM -HF COMMUNICATION TRANSCEIVER

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HF SYSTEM -HF ANTENNA COUPLER

Purpose
The HF antenna coupler matches the impedance of the antenna and feedline with the output impedance of the transceiver at the selected frequency. This results in a voltage standing wave ratio (VSWR) of less than 1.3:1.
　
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