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A. ATC Transponder
(1) External description (Ref. Fig. 005B) The face of the transponder is fitted with a handle, two attaching parts, a TEST pushbutton switch and five LEDs. The TEST pushbutton switch is used to initiate the BITE self-test. During the self-test, the transponder performs the following functions: With TEST pushbutton switch pressed for less than 5 seconds:
-stops normal processing
-performs test of full-time ROM checksum status
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ATC - Transponder Figure 005B
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-performs RAM tests
-stimulates receiver noise sources and monitors results
-checks antenna integrity
-injects simulated ATCRBS/Mode S all-call into top and bottom receivers
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samples transmitter monitor, following transmission , and verifies reply is correct
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samples power supply monitor
-performs test on non-active serial buses (TCAS, COM A/B and C/D)
-updates maintenance portion of nonvolatile memory
-returns unit to normal operation
-performs receiver test: All LEDs come on red for 2 seconds. Then the LRU status LED becomes green and the other LEDs remain red for 2 seconds. Then all LEDs go off for 2 seconds, then the test results are displayed for 30 seconds: LRU status - green for LRU with no fault, red for LRU fault; all other LEDs are off for no fault, red for fault.
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-Instead of self-test, the unit reads nonvolatile memory fault data
for the last four flight legs and the applicable LEDs come on. The functions of the LEDs are indicated on the table below:
-------------------------------------------------------------------------| LEDs | FUNCTION | -------------------------------------------------------------------------| LRU STATUS (green) | On after test indicates normal operation. | |----------------------|------------------------------------------------| | LRU STATUS (red) | On after test indicates malfunction. | |----------------------|------------------------------------------------| | ANTENNA TOP (red) | Indicates that the upper antennas are | | FAIL | incorrectly connected or are failed (comes on | | | during BITE self-test). | |----------------------|------------------------------------------------| | ANTENNA BOT (red) | Indicates that the lower antennas are | | FAIL | incorrectly connected or are failed (comes on | | | during BITE self-test). | |----------------------|------------------------------------------------| | ALTITUDE FAIL(red) | Indicates abnormal input from ALT data system | | | bus, or associated circuitry (comes on during | | | BITE self-test). | |----------------------|------------------------------------------------| | CONTROL FAIL (red) | Indicates abnormal input of 429 word data from | | | control unit, or associated circuitry (comes | | | on during BITE self-test). | -------------------------------------------------------------------------
The back of the transponder contains an ARINC 600, shell-size connector to provide electrical connections to the aircraft wiring via mount. Contact grouping is as follows :
-Top contact set and Center contact set - System interconnections
-Bottom contact set - Power supply and bonding.
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(2) Internal description (Ref. Fig. 006B) Input signals (1030 MHz interrogations/uplinks) are received at one or both of the antennas. Each received antenna signal is pulse demodulated and sent to the processing circuits where the diversity selection is made. The diversity selection determines which receiver provides the stronger (or first) signal. The selected received signal is then applied through a demodulator circuit to the processing circuits. The processing circuits determine if the interrogation is an ATCRBS interrogation, a mode S interrogation addressed to the particular aircraft or a mode S addressed to another aircraft. Depending upon the type of the interrogation, the processing circuits determine the proper reply ( if one is required) and send the appropriate reply through a message processing circuit to the diversity switching circuits. The diversity switching circuits select the antenna through which the reply will be transmitted. The reply message is transmitted through the same antenna from which the selected received signal originated. The I/O circuit is an interface circuit to receive serial ARINC 429 data, the 24 bit address input, the code altitude input and various discretes. The CPU provides the link between the I/O and the signal processing circuits. The signal processing circuits consist of a video processor, a PAM decoder and a message processor. The video processor analyzes the received signals (pulses and pulse amplitude). If the received signal is valid, the PAM decoder determines the type of interrogation. Then the decoder output is sent to the message processor where appropriate reply format is generated. The message processor output is amplified and the resultant 1090 MHz transmit signal is applied to the antennas through a diplexer/diversity switch. The received signals from the antennas are sent to the receiver stage. The 60 MHz IF output is used to drive the video processor and the message processor (DSPK function). The input of the receiver stage is filtered to reduce the susceptibility to HIRF signals. The power supply is a pulse-width modulated switching regulator. It supplies all the necessary DC voltages required by the internal circuitry. An integrated monitoring function gives protection to the power supply circuits and reset signals to the CPUs each time primary power is applied.
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