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

®

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

NOISIVERETADNOITPIRCSEDOCE

A89/42/40ESAELERLAITINI------

B99/61/30ETIRWERDNAESIVER04601

©Copyright 1999, by GARMIN Corporation. All rights reserved.

190-00133-02 Rev B A

TABLE OF CONTENTS

SECTION 1

DESCRIPTION AND OPERATION

P ARAGRAPH PAGE

1.1 INTRODUCTION ............................................................................................................... 1-1

1.2 GENERAL DESCRIPTION ................................................................................................ 1-1

1.3 TECHNICAL SPECIFICA TIONS........................................................................................ 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

DISASSEMBL Y AND REASSEMBL Y

4.1 INTRODUCTION ............................................................................................................... 4-1

4.2 INSPECTION..................................................................................................................... 4-1

4.3 FRONT SUBASSEMBL Y................................................................................................... 4-1

4.4 CLEANING ........................................................................................................................ 4-2

190-00133-02 Rev B i

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 interroga­tions 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 1-1

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 1-2

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 1-3

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 T est Harness

A Test Panel must be fabricated by the shop which meets the typical test setup criteria given Figure 2-3. Addition­ally, 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

190-00133-02 Rev B 2-1

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 connec­tor (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 solder­ing, avoid applying excess heat to the connector body, and center conductor insula­tor.

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

190-00133-02 Rev B 2-2