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Strasnuts
Joined: 10 Feb 2009
Posts: 502
Location: Salt Lake City, UT
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 Posted: Wed Apr 13, 2011 12:05 pm Post subject: TCAS ground plane |
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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:) Attached is a photo of two layers of glass. I put down one more and feathered it in.
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hotwheels
Joined: 01 Jun 2007
Posts: 240
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| Posted: Thu Apr 14, 2011 12:27 pm Post subject: Re: TCAS ground plane |
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Nice write up... You are brave to cut into the cabin top. Isn't that a structural change?
I googled GTS800...
"Feature-rich yet affordably priced, the Garmin GTS 800 system is designed to bring full TAS traffic surveillance capability well within reach of most GA..."
Almost $9000 for a GTS800. Really? Are there other alternatives out there? I'm assuming that this is the sort of box the FAA will eventually require all of us to swallow.
Thanks,
Jay
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Strasnuts
Joined: 10 Feb 2009
Posts: 502
Location: Salt Lake City, UT
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| Posted: Thu Apr 14, 2011 12:46 pm Post subject: Re: TCAS ground plane |
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I just made a hole for the coax and mounting screws. If anything all the new glass I put down on it made it stronger.
with NextGen the GTS800 won't be required but ads-b capability might be. I think it is around 2020??? There are cheaper options I'm sure like the Navworx stuff. Since I wanted real active interrogated TAS I went with the GTS800. The ads-b portion was just a bonus and since it received ads-b I thought I would get the GTX330(es) to send the ads-b out and get the entire loop.
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RV-10 SB N801VR Flying
780 Hours
SuperSTOL 60 hours |
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Tim Olson
Joined: 25 Jan 2007
Posts: 2881
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| Posted: Thu Apr 14, 2011 6:26 pm Post subject: TCAS ground plane |
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Do you get FIS-B (ads-b wx) on anything too, or are you getting XM only?
Tim
On Apr 14, 2011, at 3:46 PM, "Strasnuts" <sean(at)braunandco.com> wrote:
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I just made a hole for the coax and mounting screws. If anything all the new glass I put down on it made it stronger.
with NextGen the GTS800 won't be required but ads-b capability might be. I think it is around 2020??? There are cheaper options I'm sure like the Navworx stuff. Since I wanted real active interrogated TAS I went with the GTS800. The ads-b portion was just a bonus and since it received ads-b I thought I would get the GTX330(es) to send the ads-b out and get the entire loop.
--------
40936
RV-10 SB N801VR Flying
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Strasnuts
Joined: 10 Feb 2009
Posts: 502
Location: Salt Lake City, UT
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| Posted: Fri Apr 15, 2011 6:11 am Post subject: Re: TCAS ground plane |
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XM only. It sounds like the GTS800 won't bring in wx. Just traffic. I haven't read anything on FIS-b in the GTS manuals.
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40936
RV-10 SB N801VR Flying
780 Hours
SuperSTOL 60 hours |
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