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190-00133-02 Rev B 3-3

Figure 3-1. C620 and C635 Location

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Summary of Contents for GTX 320

Page 1: ...GTX 320 ATC TRANSPONDER MAINTENANCE MANUAL 190 00133 02 Rev B GARMIN 1200 E 151st Street Olathe KS 66062 USA 16 March 1999 ...

Page 2: ...d written consent of GARMIN International GARMIN 1200 E 151st Street Olathe KS 66062 USA Telephone 913 397 8200 or 1 800 800 1020 www garmin com REVISION RECORD Copyright 1999 by GARMIN Corporation All rights reserved N O I S I V E R E T A D N O I T P I R C S E D O C E A 8 9 4 2 4 0 E S A E L E R L A I T I N I B 9 9 6 1 3 0 E T I R W E R D N A E S I V E R 0 4 6 0 1 ...

Page 3: ...NS 1 1 1 4 EQUIPMENT DESCRIPTION 1 2 1 5 SCOPE OF MAINTENANCE 1 3 SECTION 2 SPECIAL TEST EQUIPMENT 2 1 INTRODUCTION 2 1 2 2 SPECIAL TOOLS AND TEST EQUIPMENT 2 1 SECTION 3 ALIGNMENT AND TESTING 3 1 INTRODUCTION 3 1 3 2 ALIGNMENT 3 1 3 3 TESTING 3 5 SECTION 4 DISASSEMBLY AND REASSEMBLY 4 1 INTRODUCTION 4 1 4 2 INSPECTION 4 1 4 3 FRONT SUBASSEMBLY 4 1 4 4 CLEANING 4 2 ...

Page 4: ...rscope TRANSPONDER The GTX 320 Transponder is an airborne radar transceiver It automatically receives interrogations from the ATCRBS and selectively replies with a specific pulse group code only to those interroga tions being received on the mode to which it is set Mode A no altitude information or Mode C automatic altitude information These replies are independent of and much stronger than a prim...

Page 5: ...e The Main PCB Assembly contains the following circuits IF Amplifier and Pulse Discriminator Local Oscillator and Mixer Power Supply Programmable Logic Device Light Dimming Circuitry Modulator and Transmitter 1 4 2 Front Subassembly Field Replaceable The Front Subassembly consists of the following Reply Code Switches and Mode Function Selector Front Display and Knobs Backlighting Circuitry Front P...

Page 6: ...INTENANCE Due to the overall complexity of the unit GARMIN recommends limiting field maintenance to the following Removal and Replacement of the Front Subassembly Transmitter Frequency Adjustment Transmitter Power Output Peaking Adjustment ...

Page 7: ...cated Test Panel Locally Fabricated Alignment Tool Locally Fabricated Antenna Test Cable Connector Locally Fabricated 2 3 1 Test Panel and Test Harness A Test Panel must be fabricated by the shop which meets the typical test setup criteria given Figure 2 3 Addition ally a corresponding test harness must be fabricated which allows for the necessary connections between J102 and the Test Panel Use Fi...

Page 8: ...wall opening place the ferrule over the coax braid flush against the coax outer insulation before performing the next step 4 Insert cable center conductor dielectric and shield braid through the sidewall of the connector and solder the center conductor to the center pin of the connector NOTE When using low loss cable it may be necessary to flatten the solid wire center conductor slightly so it can...

Page 9: ...190 00133 02 Rev B 2 3 Figure 2 3 Test Setup Test Harness J102 ...

Page 10: ...llowing equipment or suitable substitute is used to adjust the transmitter frequency 1 Transponder DME Test Set IFR Systems ATC 1400A 2 Power Supply Topward 2000 3 Digital Oscilloscope Tek TDS 320 or suitable equivalent 4 Voltmeter Fluke 79 5 50 Ohm Load ITT Pomona Model 3840 50 6 Transmitter Adjustment Tool Locally Made see Figure 2 1 7 Rack Mount BNC to BNC Cable RG 58 U having a total cable los...

Page 11: ...EVEL 50 dBm SLS ECHO OFF FREQUENCY POWER TOGGLE SWITCH F1 P1 ______ OK 3 Set the GTX320 transponder mode select control knob to the ON position ______ OK NOTE Allow the unit to warm up for approximately ten minutes before setting frequency 4 Rotate the frequency adjust slug C620 figure 3 1 with the screw driver portion of the transmit adjustment tool to a frequency of 1089 5 0 5 MHz Observe the fr...

Page 12: ...190 00133 02 Rev B 3 3 Figure 3 1 C620 and C635 Location ...

Page 13: ...l Time 50 nS to 200 nS Pulse Width 350 nS to 550 nS 5 Adjust C635 for maximum power output as read from the ATC1400A test set The power must be greater than 125 watts ______ 125 Watts 6 Verify that the frequency is still 1089 5 0 5 MHz If the frequency is out of tolerance then loosen the locknut on C620 set the frequency within specification and then tighten the locknut while maintaining the frequ...

Page 14: ... approximate 5 second delay before the unit transmits ______ OK 5 Rotate the mode select switch on the GTX320 to the ALT position The GTX320 shall continue to reply to valid interrogations ______ OK 6 Rotate and hold the mode select switch on the GTX320 in the TST position The GTX320 shall continue to reply to valid interrogations ______ OK 3 3 3 2 Reply Transmission Frequency 1 Set the transponde...

Page 15: ...rom the MTL in Mode A 6 Increase the RF level to 50 dB above MTL The reply rate displayed on the ATC 1400A shall be at least 90 ________ 90 Reply Rate 3 3 3 5 Reply Pulse Characteristics 1 Set the oscilloscope to the following settings PARAMETER SET POINT EXT TRIG CH 2 XMTR Detected Video CH 2 VERTICAL SENS 20mV Div HORIZONTAL SWEEP 100ns DELAYED SWEEP CENTER ON FIRST PULSE 2 Configure the ATC 140...

Page 16: ...e MTL a value of 21 dBm assuming an MTL of 71 dBm The percent reply shall be at least 90 as indicated on the ATC 1400A ______ Reply 3 3 3 7 Automatic Overload Control AOC 1 Set the SLS ECHO toggle switch back to the OFF position 2 Increase the RF level to 3 dB above the MTL 3 Set the PRF thumb wheel switches to 1200 Hz on the ATC 1400A test set The reply rate shall be 90 to 98 Note In order to obt...

Page 17: ...n 8 0 volts The unit must suppress the replies to any interrogations received during the time of the suppression pulse ______ OK 3 3 3 10 External Altittude Encoder Inputs 1 Set the digital oscilloscope to the following settings PARAMETER SET POINT EXT TRIG CH 2 XMTR Detected Video CH 2 VERTICAL SENS 20MV DIV HORIZONTAL SWEEP 5µS DELAYED SWEEP CENTER ON FIRST PULSE 2 Set the XPDR MODE switch on th...

Page 18: ...between the P1 and P3 pulses as viewed on the oscilloscope and shown in Figure 3 4 ______ OK 7 Verify that the unit is correctly encoding the altitude by observing the XPDR CODE digital display on the ATC 1400A when each set of altitude switches A through D are toggled ______ OK Figure 3 3 P1 and P3 Pulses Figure 3 4 Altitude Coded Pulses ...

Page 19: ...ll appear next to the P3 pulse on the oscilloscope See Figure 3 5 5 Rotate the mode select switch to the SBY position 6 Press the IDENT button on the transponder The reply light shall turn on for approximately 25 seconds but the unit shall not transmit ______ OK Figure 3 5 P1 P3 and SPI Pulses 3 3 3 12 Front Panel Test OFF Set the transponder mode select switch to the OFF position Only the OFF nom...

Page 20: ...ode select switch to the ALT position The ALT nomenclature and the four reply code digits shall be illuminated with a higher intensity than the OFF SBY ON and TST nomenclature ______ OK 3 3 3 16 TST Test 1 Decrease the RF level control on the ATC 1400A so that the transponder has a 00 reply rate 2 Rotate and hold the transponder mode select switch in the TST position TST OFF SBY ON and ALT nomencl...

Page 21: ... so that it returns to the ALT position The reply light shall remain on ______ OK 3 3 3 18 Numerical Reply Code Switches 1 Rotate the XPDR MODE switch on the ATC 1400A to position A 2 With the transponder mode switch in the ON position incrementally rotate the four reply code switches through each position Verify that the unit causes the ATC 1400A to display the same number on the XPDR CODE digita...

Page 22: ...190 00133 02 Rev B 3 13 Figure 3 6 ATC 1400A Test Settings ...

Page 23: ... for bent or broken pins on the 25 pin connector 4 Inspect for damage to the BNC connector 4 3 FRONT SUBASSEMBLY P N 011 00263 00 1 Remove power to the unit 2 Remove the bottom cover 5 screws to expose internal circuitry 3 Remove the four black screws holding the front bezel to the frame 4 Carefully remove the Flex Strip from the Main Board Install according to Figure 4 1 to prevent incorrect inst...

Page 24: ...2 Rev B 4 2 Figure 4 1 Front Subassembly Installation 4 4 CLEANING After reassembly clean the external surface of the transponder when inspection shows dirt smudges etc Wipe with a damp lint free static free cloth ...

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