Seeking possible solution to altitude and ADSB out issue on my Garmin set up.
Dual G3X Touch (GDU 460)
GPS175
GA 36
GTX35R
GSU 25
GMU 11
GHA 15
This set up performed beautifully for over two years. During the Condition Inspection this year there were three possible sources for this current error.
1: A local avionics A&P outfit performed the pitot/static test and the transponder inspection for IFR. The "apprentice" did the actual work and he was rather rough in handling the GSU 25 unit. He also left the ESP feature of the G3X system turned on which had the system going crazy trying to correct the perceived pitch angles during the testing.
2: I moved the GA 26X antenna that connects directly to the Primary Flight Display G3X out from inside the avionics bay (under aluminum and not getting a constant satellite connection) out under the cowling onto the same platform as the GA 36 antenna that provides WAAS GPS for the system.
3: The local avionics A&P outfit also installed the GHA 15 unit.
From the very first flight following the Condition Inspection (mid May 2025) through today the XPDR box at the top of the G3X screen (to the right of the COM and standby COM boxes) will flash a yellow "NO ADSB" above the squawked code often and less often (but still often) it will flash a yellow "NO ALT" above the squawked code before returning to the white XPDR. Class C traffic control has not mentioned not having ADSB or Mode C information but I have pulled PAPR reports and they indicate errors in reporting. Exceptions are noted on NIC, NACp and SIL. Missing Elements has red under BAlt, as well.
The avionics A&P is very busy and has asked me to take photos of various screens while flying but no potential solution has been offered. Any suggestions on where I can begin troubleshooting myself? This is an experimental aircraft and I have the repairman certificate.
