TRIG Avionics Limited, a UK-based group, has included ADS-B extended squitters in all of its 2010 TT21, TT22 and TT31 Mode S transponders, which range in price from $2200 to $2600, and are available and supported through Southeast Aerospace in Melbourne, Florida.
The TT21 and TT22 models are billed the smallest and lightest Mode S general aviation transponders, weighing just 1 pound (less than 500 grams) and fitting into a standard 2,25-inch instrument panel cutout. The TIS (traffic information service) readouts can be displayed onto a range of Garmin portable GPS products. Both transponders are designed for very light aircraft, including balloons and sailplanes, and can operate with simple battery power.
The TT31 is a direct slide-in replacement transponder for the KT-76A, KT-78A and KT-76C transponders, requiring no installation changes. It weighs 2.8 pounds and sports the same feature set as the TT21 and TT22 models, including the 1090 MHz ADS-B extended squitter for ADS-B Out capability. Designed for both new and legacy panels, the TT31 handles either 14-volt or 28-volt systems without the need for special configuring or dropper resistors. It is also compatible with both parallel and serial altitude encoders and can act as a serial altitude repeater to aid with resolving GPS altitude input needs.
To use the ADS-B Out capability the transponders must be connected to an NMEA GPS. TRIG carries the Freeflight 1201 GPS for this function, but it is possible to use your own NMEA GPS.