[July 14, 2023]

I haven't been super happy with my ADS-B in/out and Mode-C transponder. My setup is a GTX327 for Mode-C, GDL-39 to feed Garmin pilot ADS-B in, and a uAvionix EchoUAT for ADS-B out, and ADS-B in for traffic into my GRT EFIS's.

I bought a GNX375 to help consolidate the ADS-B/Transponder functionality into one unit, and also have a backup IFR GPS navigator.

The GNS375 won't solve the ADS-B traffic/weather IN for the GRT, GRT doesn't speak the language that Garmin outputs - so there will have to be something to solve this.

Well this was a little unsettling - ADS-B out was not happy. 1090ES ADS-B Out and Transponder errors looked quite bad. I made a small whip antenna to try to make this transponder happy. I really hope I didn't accidentally blow up the transmitter.

The PRESS ALT (Pressure Altitude) input also didn't work, even though I was feeding it from the GRT.

I whipped up this antenna out of HVAC ducting material and RG6.

Ground plane....grounded!

Here is my GRT Settings - 9600 baud, ALtEnc1/Altitude Encode #1.

The Serial Format also needs to be correct - Garmin/Trimble[ALT 12345] (99900).

For the GNX375 the input needs to be Alt Frmt 1 100FT.

Boom! All very very happy! I am thrilled I didn't accidentally blow up the transponder transmitter. I am glad Garmin has some intelligence in their transponder to compensate for the lack of mine!



Last Modified: August 13, 2023