Garmin GTX 320 ATC User manual

GTX 320 ATC TRANSPONDER
MAINTENANCE MANUAL
190-00133-02 (Rev B)
GARMIN
1200 E. 151st Street
Olathe, KS 66062 USA
16 March 1999
®

190-00133-02 Rev B A
®
This publication is the property of GARMIN. It may not be reproduced or transmitted in any form whether printed
or electronic, without the expressed written consent of GARMIN International.
GARMIN
1200 E. 151st Street
Olathe, KS 66062 USA
Telephone: [phone] or 1-800-800-1020
www.garmin.com
REVISION RECORD
©Copyright 1999, by GARMIN Corporation. All rights reserved.
NOISIVERETADNOITPIRCSEDOCE
A89/42/40ESAELERLAITINI------
B99/61/30ETIRWERDNAESIVER04601

190-00133-02 Rev B i
TABLE OF CONTENTS
SECTION 1
DESCRIPTION AND OPERATION
PARAGRAPH PAGE
1.1 INTRODUCTION ............................................................................................................... 1-1
1.2 GENERALDESCRIPTION ................................................................................................ 1-1
1.3 TECHNICALSPECIFICATIONS........................................................................................ 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 SPECIALTOOLSAND 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
DISASSEMBLYAND REASSEMBLY
4.1 INTRODUCTION ............................................................................................................... 4-1
4.2 INSPECTION..................................................................................................................... 4-1
4.3 FRONT SUBASSEMBLY ................................................................................................... 4-1
4.4 CLEANING ........................................................................................................................ 4-2

190-00133-02 Rev B 1-1
SECTION 1
DESCRIPTION AND OPERATION
1.1 INTRODUCTION
This manual provides all of the procedures, principles of operation, and information necessary to repair and
maintain the GARMIN GTX 320 ATC Transponder. Refer to GARMIN Installation Manual P/N 190-00133-01
for installation and operating information.
1.2 GENERAL DESCRIPTION
The GARMIN GTX 320 Transponder is an integral part of the Air Traffic Secondary Radar Beacon System
(ATCRBS, Figure 1-1), which consists of the following components:
 INTERROGATORIn the ATCRBS, the interrogator, a ground-based radar beacon transmitter/receiver, scans
in synchronization with the primary surveillance radar (PSR) and transmits ground radar interrogation signals on a
carrier frequency of 1030 ± 2 MHz, which repeatedly requests all transponders on the mode being used, to reply.
The replies that are received are mixed with the primary surveillance radar returns and both are displayed on the
same radarscope.
 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 primary radar return. The GTX 320 replies to both
Mode A and Mode C interrogations on a carrier frequency of 1090 ± 3 MHz, with a rated power of 176 watts
minimum at the antenna port. The GTX 320 is also equipped with IDENT capability which activates the Special
Position Identification Pulse (SPI) for approximately 20 seconds, identifying that transponder return from other
aircraft on the ATC scope.
 RADARSCOPEThe radarscope used by the controller displays returns from both the primary surveillance
radar system and the ATCRBS. These returns, called targets, are what the controller refers to in the control and
separation of traffic.
1.3 TECHNICAL SPECIFICATIONS
Refer to the GTX 320 Installation and Operation Manual (P/N 190-00133-01) for technical specifications.

190-00133-02 Rev B 1-2
Figure 1-1. ATCRBS System
1.4 EQUIPMENT DESCRIPTION
The GTX 320 consists of two major assemblies, the Main PCB Assembly and the Front Subassembly.
1.4.1 Main PCB Assembly (Not Field Repairable)
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 PCB Assembly

190-00133-02 Rev B 1-3
1.5 SCOPE OF MAINTENANCE
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

190-00133-02 Rev B 2-1
SECTION 2
SPECIAL TEST EQUIPMENT
2.1 INTRODUCTION
This section identifies the special tools and test equipment essential to repair the GTX 320. Standard equipment is
not listed. For any questions regarding special tools and test equipment contact the GARMIN Customer Service
Department at the address listed on Page A.
2.2 SPECIAL TOOLS AND TEST EQUIPMENT
Test HarnessLocally Fabricated
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 Figure 2-3 as an aid in fabricating the test harness.
2.3.2 Alignment Tool
The alignment tool is used to adjust the transmitter frequency (C620) and the transmitter power output (C635).
Figure 2-1. Alignment Tool

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2.3.3 Antenna Test Cable Connector
The antenna test cable incorporates a BNC connector at the test fixture antenna and a male BNC blindmate connec-
tor (GARMIN P/N 330-00198-00) at the transponder. Figure 2-2 shows the connector. Follow accepted industry
practices when installing the BNC connector. Use the following instructions when installing the blindmate BNC.
1. Trim coax outer insulation back ½ inch.
2. Trim braid (not center conductor or insulation) back ¼ inch.
3. Strip insulation back 0.120.
NOTE
If the outside diameter of the coax braid is smaller than the inside diameter of the
center connector sidewall 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 fit the slot on the RF connector center pin. When solder-
ing, avoid applying excess heat to the connector body, and center conductor insula-
tor.
5. Heat the outside of the connector sleeve and, at the same time, apply solder between the braid and the sleeve.
6. Continue to apply heat until the solder flows evenly.
7. Install 50 ohm match.
8. Insert connector cap and tack solder in two places.
Figure 2-2. Blindmate Antenna Connector

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Figure 2-3. Test Setup/Test Harness—J102

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SECTION 3
ALIGNMENT AND TESTING
3.1 INTRODUCTION
This section of the manual consists of alignment and test procedures. Perform the following procedures to iden-
tify failed units (troubleshooting) and after completing any repairs. The procedures assume familiarity with the
setup and operation of the special test equipment listed in Section 2. Units failing any part of alignment or testing
must be returned to GARMIN for repair except for the front subassembly which may be field replaced.
3.2 ALIGNMENT
Field alignment of the GTX 320 is limited to adjusting the transmitter frequency. No other attempt at alignment
should be made. Adjust the transmitter frequency before testing the unit.
3.2.1 Alignment Equipment
The following 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 loss of 1.5 dB at 1090 MHz)
3.2.2 Alignment Setup
Figure 2-3 shows a typical alignment and test setup based on the I/O of the 25 pin connector (J102) and the rear
antenna connector (J103). Use the +28 VDC input during alignment.
3.2.3 Alignment Procedure
CAUTION
Use extreme care when adjusting C620, so that the transmitter is NOT allowed to
oscillate at frequencies below 1080 MHz, and risk damaging the mixer. A failed
mixer cannot be replaced in the field, the unit must be returned to GARMIN for
repair. A failed mixer will degrade MTL by several dB.