777 AIRCRAFT MAINTENANCE MANUAL
HF SYSTEM -TUNE FUNCTIONAL DESCRIPTION
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HF SYSTEM -TRANSMIT FUNCTIONAL DESCRIPTION
General
The transmit sequence can start after the tune sequence is complete. A PTT discrete starts a series of events in the transceiver and antenna coupler.
The left and right HF systems are the same. This example shows the left system.
Transmit Mode
In the receive/operate mode, the PTT discrete to the coupler control logic circuits starts the transmit mode. The coupler control logic circuits energize relays K4 and K5, and de-energize relay K6. This puts a ground on the input to the isolation amplifier and connects the tuning elements in-line between the discriminator and the antenna.
The coupler control logic circuits connect a ground to disable the right HF coupler. It sends a key interlock signal back to the left HF transceiver.
The coupler control logic circuits do this only during these conditions:
*
Ground on the PTT line
*
No disable from the right coupler
*
Coupler control logic circuits are not in the home sequence
*
No coupler faults.
The control circuits in the transceiver energize relay K1 and tell the RF circuits to send a carrier in these conditions:
*
There is a key interlock signal from the coupler
*
There is no transceiver fault
*
There is a ground on the PTT line.
The RF circuits mix the carrier from the frequency synthesizer with mic audio. The RF signal goes through a power amplifier, the relaxed contacts of relay K2 and the energized contacts of relay K1 to the discriminator in the antenna coupler. The RF signal then goes through relays K4 and K5 and the tuning elements to the antenna. The antenna transmits the RF signal.
Sidetone
When the output from the transceiver power amplifier is more than 40 watts, a switch connects the microphone audio to an audio amplifier. The amplified audio goes to the audio jack and to the audio management unit for sidetone.
Key Event Output
The PTT discrete goes to the AIMS cabinet for the digital flight data acquisition function (DFDAF).
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HF SYSTEM -TRANSMIT FUNCTIONAL DESCRIPTION
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HF SYSTEM -FAILURE INFORMATION
Real-Time Failures
The HF communication system sends real-time failure information to the AIMS central maintenance computing function (CMCF). AIMS receives four types of failure information from HF communication system sources:
*
Transceiver failures -power supply outputs, frequency synthesizer operation, and output power level
*
Antenna coupler failures -home/tune sequence faults, and coupler arcing
*
RTP input failures -ARINC 429 frequency/mode data input
*
Transmission line failures -circuitry which connects transceiver, coupler and antenna to the RF signal.
Ground Test Failures
The AIMS CMCF sends ground test commands to the HF communication transceiver. The transceiver sends the AIMS CMCF failure information for the transceiver and the active RTP input.
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777 AIRCRAFT MAINTENANCE MANUAL
HF SYSTEM -FAILURE INFORMATION
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HF SYSTEM -TESTING
General
These are the tests for the HF communication system:
*
Left HF communication system test
*
Right HF communication system test.
HF Communication System Test
Select the system (left or right) for test.
This test makes sure that the HF communication system operates correctly. The approximate time to run the test is less than one minute. There are no airplane effects. There are no limitations or special requirements.
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777 AIRCRAFT MAINTENANCE MANUAL
HF SYSTEM -TESTING
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