User's Manual

TT21 Transponder Installation Manual 19 January 2009
00560-00 Issue AA
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2. Introduction
2.1 TT21 Description
The TT21 Mode S transponder system is an ED-73B Class 2 compliant Mode S level 2 datalink
transponder, with support for extended squitter, which also meets the relevant environmental
requirements of ED-14D. It is certified to ETSO 2C112b and ETSO C166a.
The TT21 transponder is controlled using a separate front panel controller, called the TC20. This
allows the transponder to be mounted separately from the instrument panel, and reduces the amount of
panel space taken by the transponder. The TC20 includes an altitude encoder. The TC20 is certified to
ETSO 2C112b and ETSO C88a.
The TT21 transmitter power output is nominally 130 watts, and the transponder runs from either 14
volt nominal or 28 volt nominal DC power supply with no configuration changes required.
The TT21 transponder responds to both legacy Mode A/C interrogations and to Mode S interrogations
from both ground radar and airborne collision avoidance systems. In all cases, the interrogations are
received by the transponder on 1030MHz, and replies are transmitted on 1090MHz.
2.2 Interfaces
2.2.1 TT21 Transponder Unit
The main transponder unit has a single TNC antenna connection and a single 25 way D-type connector.
The 25 way D-type interface provides the following services:
Power Input The TT21 operates on 11 to 33 Volts DC.
Front Panel Datalink A two wire data link is used to connect the TT21 and the controller.
Front Panel Power The controller is powered from the transponder.
Remote On/Off The on-off switching is on the controller, and switches this input.
Ident input External IDENT switch input.
Standby input External standby input for dual transponder installations.
“On ground” input Allows automatic flight/ground mode switching for aircraft with a squat switch.
Suppression bus I/O ARINC compatible suppression bus signal used in aircraft with other pulse
equipment, such as DME. This pin is both an input to and output from the
transponder.
GPS Input Connection to a GPS supplying position input for ADS-B position reporting.
RS232 Output Secondary RS232 interface provided for future upgrade.
2.2.2 TC20 Controller Unit
The TC20 controller has a single 9 way D-type connector. It provides the following services:
Power Input The controller receives power from the transponder.
Front Panel Datalink A two wire data link is used to connect the TT21 and the controller.
Remote On/Off The on-off switching is on the controller, and controls this output.
Altitude Output An additional serial output on the TC20 provides pressure altitude information
that can be used for baro-aiding by certain GPS receivers.
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