B.  Functional Description
(1)  
Receiver

(a)  Received signals from the antenna are routed through the Diplexer/Low Pass Filter and applied to the Preselector/Mixer. In the Preselector the signal is passed through a bandpass filter tuned to 1030 MHz. The filter output is applied to the mixer diode-And mixed with the 970-MHz local oscillator (LO) signal. The LO signal is filtered in the preselector, by a 2-pole bandpass filter prior to mixing. The 60-MHz IF signal from the mixer is applied to the IF amplifier/detector module where it is amplified and detected. The output of the IF amplifier/detector is applied to the video processor where it is amplified, pulse shaped, cleaned up by a noise suppression circuit, and elimination of P2 pulse is performed if the received signal is from the ATC ground station main lobe. The signal is then sent to the decoder/encoder circuitry.

(2) 
 Decoder/Encoder

(a)  The video processor output is applied to the decoder/encoder along with the 2.7586 MHz 2-phase clock from the decoder/encoder (D/E) oscillator. The decoder/encoder then decodes the received message, determines whether mode-A or mode-C data is requested and then developes the appropriate serial data output to be applied to the transmitter.

(3)  
Transmitter

(a)  The modulator accepts the decoder/encoder serial data outputs, adjusts the amplitude and width of the pulses and supplies the proper signal to the transmitter modulator circuit. The modulation signal modulates the transmitter oscillator which is a 1090-MHz cavity controlled pulsed oscillator. The output of the transmitter oscillator is approximately 1.5 watts peak RF power. The pulsed RF signal is applied to the exciter module where the signal is amplified to 150 watts peak RF power. This 150 watt signal is then used to drive the power amplifier module where the RF signal is amplified to 500 watts peak RF power. The power amplifier output is then sent to the Diplexer to be routed to the ATC transponder antenna.
34-53-01 Feb 20/85 Page 6
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K83193

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5C8 ATC System SchematicJun 20/88 Figure 3 34-53-01Page 7/8 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

(4)  Functional Test
(a)  Upon manual activation of the test switch, either on the unit front panel or control panel the functional test module will generate an RF pulsed signal. This signal is then applied to the local oscillator module where 60-MHz sidebands are generated on the local oscillator signal. These sidebands are a pulsed pair which are properly spaced to represent a valid mode interrogation. The LO signal with the 60-MHz sidebands is applied to the mixer and a 60-MHz IF signal is generated. From this point on the signal is processed as a valid interrogation and the monitor/reply light as well as the light on the front panel will come on. The front panel light will go out immediately when the front panel switch is released, however, the control panel monitor/reply light will remain on for the prescribed 15 seconds after the last reply.
5C8 
Jun 20/88  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  34-53-01 Page 9 

ATC SYSTEM - TROUBLE SHOOTING
EFFECTIVITY
GJ B-2524

1. General
A.  The following trouble shooting procedures are based on performance of the operational and system tests and are presented in tree-type format.
B.  When a test step does not check out, follow the connecting line to the box containing the trouble symptom. Continue to follow a single line by analyzing the results of each test step until the required corrective action is determined. Perform the specified corrective action, then repeat the step at which the failure was encountered. When all steps in a path check out, the system is operable.
C.  All trouble shooting procedures are based on the assumption that wiring is OK and that electrical power is available. If the corrective action in the procedure does not correct the problem, check wiring using the wiring diagram.
D.  The trouble shooting procedures are for either ATC system No. 1 or ATC system No. 2 (if installed). 
2.  Prepare for Trouble Shooting
A.  Provide electrical power.
B.  Check that required ATC, interphone and air data system circuit breakers on P18 and P6 panels are closed.
C.  Set function selector to standby.
D.  Select transponder to be tested. 
NOTE: Allow at least 1-minute warmup.
E.  Perform operational or system test (34-43-0) to isolate malfunction.
5C8
Jun 20/88 34-53-01 Page 101
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.