ADF SYSTEM -DIGITAL INTERFACE
General
The components that interface with the ADF receivers on ARINC 429 data buses are the left and right CDUs and the left and right AIMS cabinets.
CDU Interfaces
The CDUs supply tune inputs directly to the ADF receivers on the NAV aid tune buses when the tune inputs from the AIMS cabinets fail.
AIMS Cabinet Interfaces
The ADF receivers get tune inputs from the flight management computer function (FMCF) in the right AIMS cabinet. The left and right ADF receivers get tune inputs on the left and right NAV aid tune buses from the right AIMS cabinet.
Test commands come from the central maintenance computer function (CMCF) in the left AIMS cabinet. The left and right ADF receivers get test commands on the left and right CMCF buses from the left AIMS cabinet. The AIMS cabinets also give flight leg data to the ADF receivers.
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ADF SYSTEM -ADF RECEIVER
Purpose
The ADF receiver calculates bearing to a station that transmits in the frequency range of 190 KHz to 1750 KHz. The receiver also receives station identifiers and AM broadcasts.
Description
The ADF receiver operates on 115v ac power. The receiver has built-in test equipment (BITE) that monitors receiver operation and data inputs.
There is a test switch on the front panel of the receiver. When you push the test switch, a self-test begins. At the end of the test, the status of the ADF receiver and tuning inputs shows.
Use the maintenance access terminal (MAT) to do a test of the ADF receiver.
Training Information Point
The maintenance manual and the fault isolation manual do not have a task for the line maintenance technician to do a test from the front panel of the ADF receiver. You must do all tests for the ADF receiver from the MAT or a PMAT.
Many LRUs on the 777 are compatible with other model airplanes that do not have a central maintenance computing system (CMCS). For that reason these LRUs have a front panel test feature.
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ADF SYSTEM -ADF ANTENNA
Purpose
The ADF antenna receives electromagnetic signals from ground stations. The loop antenna receives the magnetic part of the ground station signal, and the sense antenna receives the electrical part of the signal.
Description
The antenna assembly is a one piece molded shell. The antenna assembly has:
*
Loop antenna elements (2)
*
Sense antenna (1)
*
Amplifiers (3), one for each antenna element
*
Transformers (3), one for each antenna element.
The ADF antenna elements each have an amplifier and output transformer. The amplifiers receive 12v dc power from the ADF receiver. The left ADF receiver sends power to the left antenna and the right ADF receiver sends power to the right antenna.
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ADF SYSTEM -FUNCTIONAL DESCRIPTION
Power
The ADF receiver power supply receives 115v ac and supplies all the voltages for the internal circuits.
Antenna Inputs
The receiver circuits get radio frequency (RF) signals from the antenna. The antenna amplifiers receive 12v dc from the antenna control circuits in the ADF receiver. The RF signals from the antenna elements go through amplifiers and transformers then to the receiver circuits.
Tuning Inputs
The ADF receiver input/output data processor receives manual tune inputs from the right AIMS cabinet and alternate tune inputs from the CDUs. If the right AIMS cabinet tune input fails, alternate tune inputs come directly from the onside CDU.
When the AIMS cabinet fails, the CDU sets the frequency source select discrete to ground. This changes the tune input port to the CDU.
Receiver Operation
The data processor sends the tune frequencies to the receiver circuits.
For normal operation, the receiver circuit removes the audio signal from the RF signal and sends it to the audio processor. The audio goes through an audio amplifier then to the AMU.
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