Transponder Options

Transponder Options

The following is a list of popular transponders used by GRT customers. The Trig TT22 is recommended for its price, remote interface and ADS-B Out (Extended Squitter) capability. This list is not all-inclusive; our built-in encoder will feed most Mode C and Mode S transponders including Becker, Microair and King, with support for both Grey code and serial encoder data.

 Manufacturer Model Type Mount Retail Price Available through GRT
Garmin    GTX 327  Mode C Panel  $1,789 No
 GTX 330 / 330-ES  Mode S Panel $3,649 No
Trig      TT21  Mode S
Remote  $1,875*  Yes
TT21  Mode S
 Panel $2,239 No 
TT22 Mode S
Remote  $2,200* Yes
TT22  Mode S
Panel  $2,499 No
TT31 Mode S
Panel  $2,675 No
 Sandia  STX 165R Mode C  Remote  $1,550  Yes

Retail prices are from a reputable dealer for comparison purposes only – may not be current.


Remote Mount interfaces apply to HXr only.

*GRT price includes single-display remote serial adapter for HXr. Dual-display adapter is available for $175. Dual-display adapter allows two display units to control transponder, providing redundancy if one display unit is lost.

†TT21 does not comply with U.S. 2020 ADS-B mandate, which requires Class 1 transponder (higher output wattage).


Transponder Documentation

Here you’ll find all user documentation created by GRT for popular transponder options, including mounting templates and supplements for wiring, setup and use.

  Revision Date
Trig TT21/TT22 Supplement for HXr  A2 5/28/2014
Trig TT21/TT22 Mounting Tray and Overall Dimensions  A 11/06/2012
Trig TT21/TT22 Serial Adapter Dimensions*  1 11/06/2012
Trig TT21/TT22 Wiring Diagram for HXr  1 11/06/2012
Trig TT22 Unit Photos*  1 11/06/2012
Garmin GTX327 GRT Supplement  A 12/15/2014
Garmin GTX330 GRT Supplement  A1 10/23/2013

*Note: Trig serial adapters have the same dimensions as the drawings and photos shown, but now have a metal case.