My brother-in-law has a Garmin GTR200 Comm in his RV-3 and has been having a devil of a time getting it to transmit farther than 30 ft. It receives fine. We've triple-checked the wiring, and put a new antenna on which is very well-grounded. At this point we suspect the Comm radio itself, but before we send it off to Garmin, would like to put a working GTR-200 in the tray and see if everything works OK. Willing to fly to whatever airport you are at, and buy lunch!