Garmin International announced the GTX 335D and GTX 345D, antenna diversity versions of its very popular GTX 335 and GTX 345 Automatic Dependent Surveillance-Broadcast (ADS-B) Out transponders, on March 25 at the Aircraft Electronics Association convention in Palm Springs, California.
The GTX 335D and GTX 345D are intended for aircraft that may require a diversity solution, meaning transponder antennas on both the bottom and top of the fuselage. Like the products on which they are based, the GTX 335D is a Mode S transponder that provides ADS-B Out, while the GTX 345D adds ADS-B In traffic and weather that can be displayed on compatible avionics and mobile devices. Remote-mount versions of both also are available.
Dual antennas on the GTX 335D and 345D provide superior operational coverage. Compared to a single antenna that is mounted on the bottom of the aircraft, diversity antennas help reduce antenna “shading” caused when the aircraft turns or maneuvers, Garmin said, and improve line-of-sight visibility, allowing the transponder to more robustly send and receive ADS-B transmissions from other participating aircraft.
Interest in ADS-B antenna diversity shot up when Nav Canada indicated in January that it wanted to mandate ADS-B Out with antenna diversity. Nav Canada is the lead air navigation service provider in Aireon, a space-based ADS-B joint venture between Iridium Communications and a number of governmental and regional air navigation service providers. Aireon ADS-B payloads aboard each of the 75 Iridium NEXT satellites in low earth orbit receive ADS-B broadcasts and relay them to air traffic controllers on the ground.
The agency announced its proposed ADS-B Out performance requirements mandate in a January webinar. On March 5, AOPA and a number of other aviation organizations—in both the United States and Canada—wrote Nav Canada, expressing concern about the diversity mandate; Nav Canada has not yet responded.
Garmin’s development of the GTX 335R and GTX 345R started well before the Nav Canada mandate came to light, however. “We did it because owners have been asking for antenna diversity,” said Jessica Koss, Garmin aviation media relations specialist. “We didn’t want to be reactionary.”
Remote-mount versions of the GTX 335D/GTX 345D provide a diversity transponder-based ADS-B solution for select G1000, G1000 NXi, and G3000-equipped aircraft. The GTX 335D/GTX 345D also can interface with a variety of other Garmin avionics, flight displays, and mobile devices. Display capabilities vary; visit the Garmin website for full compatibility details.
The GTX 335D and GTX 345D ADS-B transponders have received FAA technical standard order authorization, and deliveries for select installations will begin next week. Garmin will have an updated aircraft model list supplemental type certificate late in the second quarter of 2019 comprising hundreds of aircraft makes and models. The GTX 335D and GTX 345D list for $6,495 and $7,995, respectively; the non-diversity GTX 335 and GTX 345 list for $2,995 and $4,995.
Although the capabilities, functionality, and operation of the new transponders are the same as the non-diversity products, which remain in production, Garmin said the diversity transponders are of a completely new design—which means that existing GTX 335 and GTX 345 transponders cannot be updated to add diversity capabilities. More information about Garmin’s ADS-B solutions can be found online.