(5)
The encoder output pulses are amplified and shaped in the modulator, and the resultant signal is used to trigger the RF power oscillator in the transmitter.
(6)
The modulator output pulses are applied to the grid of the RF power oscillator in the transmitter cavity, which delivers a 500-watt peak power pulse at 1090 MHz through the isolator and rf diplexer to the antenna for reception by the ATC ground radar interrogator system. The isolator serves to isolate the transmitter circuits from the effects of antenna load variations. The RF diplexer isolates the transmitter from the receiver circuits, with both effectively connected to the same antenna.
(7)
The self-test circuits are connected to one of the preselector cavities by means of a coupling probe. The self-test circuits permit a rapid check on the operational status of the transponder.
(8)
The reply from the encoder to the modulator is determined by the setting of the function selector switch on the ATC control module. In mode A (normally used in domestic operation) the system will respond to an 8 microsecond pulse pair interrogation and in mode B (normally used in Europe) to a 17 microsecond pulse pair interrogation. When interrogated in either mode A or B, the system sends a pulse coded reply consisting of from two to eight accurately spaced pulses on a frequency of 1090 MHz.
EFFECTIVITY
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ATC CONTROL MODULE
ATC System Block Diagram
Figure 3
EFFECTIVITY CONFIG 2AF 101-151
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(9)
The coding of this identification reply is determined by the setting of the identification code selector switches on the ATC control module. Additionally an IDENT button in the ATC control module, when pressed momentarily during mode A or B interrogation, causes an additional single identification pulse to be transmitted for 6 to 30 seconds at the end of each train of coded reply signals.
(10)
Altitude reporting may be initiated in mode A, or B if the ALT REPORT switch is not in the OFF position. Altitude reporting is initiated upon the reception of a 21 microsecond interrogation pulse pair from the ground station. During altitude reporting, digital altitude data from the CADC is applied to the encoder in the ATC transponder. The position of the ATC switch on the ATC control module determines whether altitude data from CADC 1 or CADC 2 is utilized by the ATC system.
(11)
The operational status of the two ATC transponders is controlled by the function selector switch and the ATC TR switch on the control module. With the function selector OFF, both transponders are off. When the function selector is set to STBY the power supply provides power to all circuits in both transponders. The ATC system is placed in operation by setting the function selector to ON. The turn-on signal is applied to the modulator of either ATC 1 or ATC 2 transponders as determined by the position of the ATC TR switch. Time delay circuits in the modulator inhibit the output of the modulator until after the transmitter tube has reached proper operating temperature. The LO SENS position of the function selector switch provides a signal to the transponder which reduces the IF amplifier circuits in the receiver. The LO SENS position is generally used upon request of the ground controller.
(12)
Switching of the altitude data from either of the two central air data computers (CADC) to the ATC system is illustrated in figure 4. Twelve altitude encoding switches within each CADC are positioned in accordance with the coded digital equivalent of the airplane altitude. A flag switch within the CADC is closed whenever the altitude data is valid and the CADC is operating normally. With the ATC switch on the ATC control module set to position 1, current flows through the ATC switch, through the flag switch, and through any of the altitude encoding switches that are closed to cause a voltage drop across the corresponding resistors in ATC 1 and 2 transponders. The digital altitude code is picked off of the twelve resistors and encoded for transmission to the ground station by the transponder which is on. With the ATC switch in position 1, therefore, both transponders receive altitude data from CADC 1. Likewise, with the ATC switch in position 2, both transponders receive altitude data from CADC 2.
EFFECTIVITY
AF 101-151 with AEB 34-587 CONFIG and AEB 34-607 02 Page 6 Apr 25/96
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B. Control
(1) Turn On Procedure
(a) Turn on the airplane electrical power lighting, and air conditioning systems. Refer to 24-22-00.
CAUTION: MAKE SURE THAT THE EQUIPMENT COOLING SYSTEM IS
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本文链接地址：747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航4(60)
