ATC/MODE S TRANSPONDER SYSTEM -ATC ANTENNA

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ATC/MODE S TRANSPONDER SYSTEM -ATC COAX RELAY

General
The ATC coax relays connect the active ATC/mode S transponder to the top and bottom ATC antennas.
The electrical connector has an input from these components:
*
ATC antenna switch circuit breaker

*
ATC control panel.

The ATC coax relays supply an RF interface for the ATC system interrogation and reply signals. These are the connectors:
*
Right ATC/mode S transponder connector

*
ATC antenna connector

*
Left ATC/mode S transponder connector.

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ATC/MODE S TRANSPONDER SYSTEM -ATC COAX RELAY

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777 AIRCRAFT MAINTENANCE MANUAL

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ATC/MODE S TRANSPONDER SYSTEM -INPUTS AND CONTROL

Transponder Panel
The transponder panel controls the operation of the ATC/Mode S transponders.
The microprocessor in the control panel gets inputs from these:
*
Code selectors

*
IDENT switch

*
Mode selector.

The microprocessor changes these inputs into ARINC 429 digital data. The transponder panel sends this data on an ARINC 429 data bus to the selected transponder.
The digital data contains:
*
The identity code the flight crew selects to reply to mode A interrogations

*
Digital discretes for the position of the IDENT switch

*
Digital discretes for ALT RPTG OFF or ON.

The standby analog discrete selects one transponder for operation. The selected transponder receives an open discrete from the control panel. A ground discrete goes from the panel to the other transponder to put it in the standby mode. This discrete also goes to the ATC antenna coax relay to connect the two ATC antennas to the selected ATC/Mode S transponder.
EFFECTIVITY
BEJ ALL

Air/Ground Input
The transponder receives an air/ground discrete from an air/ ground relay. The CPU uses the air/ground discrete to count flight segment in the fault history non-volatile memory. This discrete also prevents mode A and mode C replies when the airplane is on the ground.
ATC/Mode S Transponder Inputs
The transponder has an input/output (I/O) that has an interface with the ARINC 429 data and analog discretes from the panel.
Control Inputs
The digital data bus from the panel contains two digital discretes. One shows if the function selector on the panel is in the ALT RPTG OFF (altitude reporting off) position. If it is, the CPU does not let the transponder make a mode C reply.
The other digital discrete from the control panel shows the position of the IDENT switch on the control panel. The pilot momentarily pushes the IDENT switch at the request of the ground station. When this happens, the transponder sends a special position identification (SPI) pulse at the end of every normal mode A reply. It continues for 18 seconds. The SPI causes the airplane identification to show on the air traffic controller radar screen.
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ATC/MODE S TRANSPONDER SYSTEM -INPUTS AND CONTROL

Altitude Inputs
BEJ 006-999
The AIMS cabinets send barometric altitude to each transponder. Each transponder has two sources of altitude data. The altitude source selector on the panel sends an analog discrete to select the normal or the alternate altitude source.
BEJ 001-005
The left AIMS cabinet sends ADIRU barometric altitude to the left transponder. The right AIMS cabinet sends SAARU barometric altitude to the right transponder. Each transponder has only one source of altitude data.
BEJ 006-999
Altitude input number one is the normal source for the left transponder. Input number two is the normal source for the right transponder.
BEJ 001-005
Altitude input number one is the normal source for the left transponder.
BEJ ALL
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ATC/MODE S TRANSPONDER SYSTEM -INPUTS AND CONTROL

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ATC/MODE S TRANSPONDER SYSTEM -INPUTS AND CONTROL

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