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.
