Cavalier Avionics is an authorized Garmin dealer and is the exclusive Garmin dealer at LancairTalk. Get your avionics, panels, harnesses and all your tools and materials. We can supply Garmin experimental and certified avionics directly to LancairTalk members. Install facilities are available.
Based on latest Install manual, I have not seen any requirement for a ground plane. The Legacy I viewed at OSH in the Garmin viewing had the GHA 15 installed also. I am installing one also. If you want one, let me know, I have special deals on the GHA 15. Thanks for the question.