(c)
Each reply pulse train consists of zero to 12 pulses within two framing pulses. When the IDENT button is pressed, an identification pulse follows the second framing pulse for several transmissions. The number of pulses in the pulse train is determined by the identification code selected on the control module for mode A or B replies or the presence or absence of altitude data from the Central Air Data System for mode C replies.
(2)
Receive
(a) The RF energy from the ATC antenna is filtered, unwanted signals are rejected, and the resulting signal is mixed with a local oscillator to produce an IF signal. The IF signal is sent through a decoder consisting of an amplifier and video detector. The decoder determines the validity of the interrogation. A mode trigger pulse is sent to the encoder for each valid interrogation signal. An automatic overload control circuit reduces the IF amplifier sensitivity if the number of reply pulses or external suppression pulses exceeds a preset level.
(3)
Transmit
(a)
The encoder receives the trigger from the decoder, generates the proper number of reply pulses and routes them to the modulator. The modulator develops a series of high voltage pulses for transmission by the ATC antenna.
(b)
The encoder generates a suppression trigger for each mode trigger pulse which disables the decoder during transmissions. The encoder also routes suppression pulses to the DME System (Ref 34-55-00). The DME System when transmitting sends suppression pulses to the ATC System. This prevents simultaneous transmissions from different L-band systems.
(4)
Monitor
(a) During normal operation, the transmitted output is sampled and applied to a monitor circuit. A reply or MONITOR light on the transponder comes on momentarily after four successive reply pulse trains. The light also comes on when the TEST button on the control module is pressed.
B. Control
(1) Turn On Procedure
EFFECTIVITY LH ALL; AT ALL; AZ ALL; GN
ALL; MD ALL; SN ALL; AF 152-199; VM ALL; EXCEPT CONFIG 1 AIRPLANES WITH EAB 34-587 01 Page 9 AND 34-607 Apr 25/96
34-53-00
(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
_______ OPERATING BEFORE TURN ON OF THE ELECTRICAL OR ELECTRONIC SYSTEMS OR HEAT DAMAGE COULD RESULT. EQUIPMENT COOLING SYSTEM MUST BE SET FOR NORMAL COOLING AS DESCRIBED IN 21-58-00.
(b)
On LH 001-010, 031-050, 071-081; AZ 201-219; SN ALL, set the function selector switch on the ATC control module to OFF.
(c)
On AF 152-199; AZ 221-299; LH 011-030, 051-070, 082-099, GN ALL MD ALL; VM ALL; SN 351, 352, set the function selector switch on the ATC control module to STBY.
(d)
On AT ALL, set the ATC transfer switch on the ATC control module to STBY.
(e)
Close the following circuit breakers:
ATC 1 AC
ATC 2 AC
(f)
Select ATC transponder 1 or 2 as desired using the ATC switch on the control module.
(g)
On LH 001-010, 031-050, 071-081; AZ 201-219; SN 301, 302, set the function selector to A or B as desired.
NOTE: The function selector may be turned directly from OFF
____ through STBY to A or B, however, in this case there is an automatic built-in warm-up delay of 60 seconds before final power is applied to the output stage.
(h)
On AF 152-199; AZ 221-299; LH 011-030, 051-070, 082-099, GN ALL; MD ALL; VM ALL; SN 351, 352, set the function selector to A or B as desired.
(i)
On AT ALL,
set the MODE switch to A or B as desired.
(2) Shutdown
(a)
On LH 001-010, 031-050, 071-081; AZ 201-219; SN 301, 302, set the function selector on the ATC control module to OFF.
(b)
On AF 152-199; AZ 221-299; LH 011-030, 051-070, 082-099, GN ALL; MD ALL; VM ALL; SN 351, 352, set the function selector on the ATC control module to STBY.
(c)
On AT ALL,
set the ATC switch to STBY.
EFFECTIVITY
LH ALL; AT ALL; AZ ALL; GN
ALL; MD ALL; SN ALL; AF 152-199; VM ALL; EXCEPT CONFIG 1 AIRPLANES WITH EAB 34-587 01 Page 10 AND 34-607 Apr 25/96
34-53-00
ATC SYSTEM - DESCRIPTION AND OPERATION
______________________________________
1. General_______(See figure 1.)
A. The air traffic control (ATC) system, when interrogated by a ground station, automatically transmits a pulse coded reply signal to the ground station. This reply signal is used to identify and locate airplane equipped with ATC equipment for air traffic control. The reply signal is used to display airplane range, bearing, altitude, and identity on the ground station radarscope.
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