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  #1  
Old 04-13-2011, 03:03 PM
Strasnuts Strasnuts is offline
 
Join Date: Jan 2009
Location: Salt Lake City, Utah
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Default GTS800 ground plane

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
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  #2  
Old 04-13-2011, 07:25 PM
Wayne Gillispie Wayne Gillispie is offline
 
Join Date: Apr 2009
Location: USA
Posts: 1,494
Default Maybe Van's should offer a 6 place

so we could have more windows, more fiberglass, bigger engine and more room for antennas.

I installed 22" round X .016" ground plane centered over the rear seats on bottom side for my Com 2 SL-40. I roughened surfaces. Acid Etched/Alodined metal then epoxied to cabin cover, then applied filler around the edges. I then fabricated my own little overhead junction boxes in front and back with 3/8" x 1" conduit in between for running coax/wires. I decided to wait on the ads-b for awhile and let the prices come down and selection go up. I can't afford it right now anyway.

Thanks for the heads up. You will probably be one of the few RV's with that nice piece of equipment on board. I am sure it will come in very handy and increase the safety margin.
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  #3  
Old 04-14-2011, 08:22 AM
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Bill.Peyton Bill.Peyton is offline
 
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Default

Sean,
You should try to move it to the tailcone temporarily and see if that works. At the frequency that it uses, the tailcone should be more than adequate for the ground plane. You could then move the GPS antenna on to the cabin top as it does not require a ground plane. It would certainly be worth a try. The reason the ground plane does not work on the inside is the capacitance created by the cabin top thickness. YOu might be able to route out a spot into the honeycomb for the antenna where the inside ground plane would bre in direct contact with the antenna base. The honeycomb should have little effect on the performance of the antenna.

Out of curiousity, does the GTS800 also receve and display the ADS-B weather on the G3X. I have been debating the G3X system, but want to make sure I can receive the total ADS-B products

Bill
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  #4  
Old 04-14-2011, 08:34 AM
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mburch mburch is offline
 
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Default

Quote:
Originally Posted by Bill.Peyton View Post
Out of curiousity, does the GTS800 also receve and display the ADS-B weather on the G3X. I have been debating the G3X system, but want to make sure I can receive the total ADS-B products.
The GTS 8xx is a traffic system, no weather features. Displaying GTS traffic data on the G3X system is planned for the future, but since this will require a change to the certified GTS software, it unfortunately will not happen right away. I know it's on the roadmap, though!

mcb
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  #5  
Old 04-14-2011, 03:40 PM
Strasnuts Strasnuts is offline
 
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Location: Salt Lake City, Utah
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Default

Bill,

I have XM on the G3X system and doubt Garmin would take that money away from them and display ads-b wx. Don't know if it is true but heard XM weather has a lot more features than ads-b will. Maybe Tim O could pipe in. I bet he would know. As for moving my antenna on the tailcone, it is a no no for me. I have two GPS antenna holes already and have done a lot of R and D to mount the TAS antenna where it will work best per the instructions. I really like the G3X system and I'm extremely happy with the purchase. I believe the other brands are great too so it's just personal preference. One early complaint I had with the G3X was the size of the screens. I thought they looked too small at first. After installing them I think they are great. They are literally right in front of your face so size doesn't matter! At least I will keep trying to tell everyone that.
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  #6  
Old 04-14-2011, 06:58 PM
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Bill.Peyton Bill.Peyton is offline
 
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According to the Navworx rep, ADSB will have nexrad, metar, taf, winds aloft, and I believe, freezing level. Not quite as much as XM, but it is free. This should be up and running by the end of the year for 90% and by the end of 2012 for 100%. I currently use XM, and I am happy with it also.
I almost purchased the G3, but I think I am going to hold out for the AFS system this year.
I regards to your ground plane issue, when you tried putting the ground plane inside the cabin, did you have a ground strap running to the actual antenna, or did you have the bolts which hold the and antenna connected to the ground plane? Simply putting the ground plane under the antenna without physically connecting it really won't work. There will be of course, a mismatch with the ground plane physically located 2" below the antenna ground plane, but with some additional wires running through the cabin cover to the ground plane you may get it to work
Bill
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  #7  
Old 04-14-2011, 07:14 PM
Strasnuts Strasnuts is offline
 
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Location: Salt Lake City, Utah
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Default Ground strap

I did try that. Both examples. I have the aluminum tape still under the plate and wrapped through the coax hole onto the interior backing plate and also a ground strap to the airframe. I removed the ground strap after the testing was successful without it. I guess it would be nice to have if I get hit by lightening. I hope ADS-b wx is successful to drive the cost down for XM wx. I don't know if Sirius is even making money yet??
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  #8  
Old 04-14-2011, 08:14 PM
johnny stick johnny stick is offline
 
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Default ground plane

Not being an expert, but knowing a little about antennas, the ground plane needs to be right under the antenna. If the ground plane is on the other side of the antenna, it could make the antenna appear longer to the incoming signal and cause the antenna to be out of tune.
From my radio days, the ground plane makes the antenna size appear to be twice as long as the real antenna element. If the fiberglass on the cabin top is 1/2" thick, then a ground plane on the inside would make the antenna appear to be 1" longer to the incoming signal.
Still not sure why the holes caused a problem though.
JMO
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  #9  
Old 04-15-2011, 09:08 AM
Strasnuts Strasnuts is offline
 
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Default Makes Sense

Johnny,
I bet you are right. The ground plane had to be right under the antenna. After knowing this, it is pretty easy to mount a plate on the fiberglass. I just wish I didn't spend all that time making plates for the inside.
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