Thought I would share my experience installing a ground plane on the RV-10 cabin top for the GTS800 and hopefully save some building time for others. Like every other Garmin device, the installation manual gives you a detailed list of priorities for mounting and location of antennas. Some items, such as the GMU44 would only meet all the criteria if it was mounted to a 20 foot rigid line hanging off the plane. My experience with Garmin is they are extremely sensitive units. This is great for operation but tough for installation. The GTS800 is no different. The first location priority is to mount the top GA58 antenna on the highest and most forward location on the aircraft with no antennas in front of it. It has to be mounted level and in the middle. OK so far so good. Next it needs an 18 x 18 ground plane. WHOA. We have roughly a 10 x 30 spot on the top between the doors hinges. I have the sweet Aerosport overhead console installed and it has the 10 x 30 dimensions inside. I came to the conclusion I could use a copper wire mesh inside the overhead console with a backing plate. The ground plane should see through the honeycomb and fiberglass. I could get the square inches needed but not the 18 x 18 width. I also mounted a bottom monopole antenna for the TAS so there will not be any shadowing from the fuselage. This is a simple transponder blade mounted right below the GA58. BTW the top requires 4 coax and the bottom requires 1. I then powered up the plane, configured the GTS800 to talk to the 430w and 330es. Check the self test on the TAS and "FAILED" shows up.
The configuration program is a downloadable exe. for windows that hooks to the GTS800 via USB connection. You can configure all the settings and diagnose problems. There is also an assert file you can save as a txt file and email to Garmin for troubleshooting. Mine returned with a "receive cal" fault, which translates to coax or/and antenna ground plane. I was pretty confident with my coax crimping abilities and really believed it was the ground plane size. After a few attempts of backing plates and wire mesh combinations I finally tried placing a 20 x 20 scrap sheet of .016 to the top of the cabin. Obviously this is overhanging the doors and is only for testing purposes. The self test passed with the giant ground plane on TOP of the cabin. After trying different sizes on the top and the bottom it was very apparent that I HAD to have a ground plane on the top of the cabin under the GA58. I don't know how Cirrus does it but their new planes show the GA58 on the top between the doors. Their span is even narrower than the RV-10. They must use a mesh inside the glass or carbon fiber. Just a 10x 18 span of aluminum tape on the top of my cabin worked great. BTW I also tried grounding the ground plane to the airframe and that had no affect on passing or failing the self test. I also wrapped aluminum tape from the inside ground plane/backing plate through the coax hole and made a footprint of the antenna out of the aluminum tape. I left this on.
I called Garmin and they said to move the antenna to the tailcone area. This wasn't an option for me. #1 it's not level, #2 my two gps antennas are already there, #3 too close to my GMU44, #4 too far back on the plane, #5 not inline with the bottom antenna anymore.
After knowing I had to make a ground plane on the top of the cabin, I slowly cut it down in size to see how small I could make it while still passing the self test. I eventually ended up with a 6 x 18 piece of .025 aluminum. I wanted thicker than .016 so it wouldn't de-laminate from the cabin. Before I attached it I ran the self test. It passed. I then wanted to epoxy it to the cabin top and glass over it with a few sheets of fiberglass. I drilled the rivet holes for cs4-4's and ran the test.....FAILED. WTH??? I thought it was a mistake and ran it again....FAILED. I couldn't believe it was the rivet holes so I temporarily taped over them with the aluminum tape......PASSED! Just the open holes caused the antenna to fail consistently. I thought the rivets in the holes would cure it and they did. I now have a glassed over ground plane 6 x 18 on the top of the cabin and it has worked flawlessly for 12 hours now. I still don't know why the ground plane doesn't work inside the cabin. It must be a distance from the antenna deal but I tried everything inside.
This is also a good example why I didn't paint my plane before my first flight
The configuration program is a downloadable exe. for windows that hooks to the GTS800 via USB connection. You can configure all the settings and diagnose problems. There is also an assert file you can save as a txt file and email to Garmin for troubleshooting. Mine returned with a "receive cal" fault, which translates to coax or/and antenna ground plane. I was pretty confident with my coax crimping abilities and really believed it was the ground plane size. After a few attempts of backing plates and wire mesh combinations I finally tried placing a 20 x 20 scrap sheet of .016 to the top of the cabin. Obviously this is overhanging the doors and is only for testing purposes. The self test passed with the giant ground plane on TOP of the cabin. After trying different sizes on the top and the bottom it was very apparent that I HAD to have a ground plane on the top of the cabin under the GA58. I don't know how Cirrus does it but their new planes show the GA58 on the top between the doors. Their span is even narrower than the RV-10. They must use a mesh inside the glass or carbon fiber. Just a 10x 18 span of aluminum tape on the top of my cabin worked great. BTW I also tried grounding the ground plane to the airframe and that had no affect on passing or failing the self test. I also wrapped aluminum tape from the inside ground plane/backing plate through the coax hole and made a footprint of the antenna out of the aluminum tape. I left this on.
I called Garmin and they said to move the antenna to the tailcone area. This wasn't an option for me. #1 it's not level, #2 my two gps antennas are already there, #3 too close to my GMU44, #4 too far back on the plane, #5 not inline with the bottom antenna anymore.
After knowing I had to make a ground plane on the top of the cabin, I slowly cut it down in size to see how small I could make it while still passing the self test. I eventually ended up with a 6 x 18 piece of .025 aluminum. I wanted thicker than .016 so it wouldn't de-laminate from the cabin. Before I attached it I ran the self test. It passed. I then wanted to epoxy it to the cabin top and glass over it with a few sheets of fiberglass. I drilled the rivet holes for cs4-4's and ran the test.....FAILED. WTH??? I thought it was a mistake and ran it again....FAILED. I couldn't believe it was the rivet holes so I temporarily taped over them with the aluminum tape......PASSED! Just the open holes caused the antenna to fail consistently. I thought the rivets in the holes would cure it and they did. I now have a glassed over ground plane 6 x 18 on the top of the cabin and it has worked flawlessly for 12 hours now. I still don't know why the ground plane doesn't work inside the cabin. It must be a distance from the antenna deal but I tried everything inside.
This is also a good example why I didn't paint my plane before my first flight