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[Dickey]

Thanks for the link Marcus. I've been wondering how long the FAA would allow this to go on.

Anyway, here's the skinny on how the GPS 20A was installed in our Carbon Cub FX.

Wiring Configuration:
We have paired the GPS 20A to the GTX 23ES using RS-232 data. This means that the 20A is only providing position compliance to the transponder and it IS NOT being used as the navigation source for the GDU. It can be used as the position source for navigation, but you will have to figure a way to keep it powered by the IBBS in the event of an electrical failure. It will also make the harness and connections more complex because of IBBS connections and you have to add another "node" to the CAN bus backbone. Garmin says the user will not see any difference in performance between the current GPS antenna and the 20A so we opted to just use it for ADS-B position compliance.

Antenna selection and location:
We refitted the aluminum turtle deck with the Comant, CI 2480-201 combination VHF/GPS antenna. It is a WAAS antenna and is about 6" shorter than the RAMI. Garmin would prefer you used their GA 35 GPS antenna but, that would mean an extra ground plane, extra brackets, and extra weight just so we could add an extra antenna. The Comant is listed as an acceptable antenna in the G3X manual (the important thing is dB gain between 16 and 25). With this method, the additional weight from the antenna is only 0.1 pounds (this doesn't include the 20A and its harness or coax) vs. keeping the RAMI VHF antenna and adding another 0.47 lbs with the GA 35 GPS antenna.

Location and connection of the GPS 20A:
I mounted it just behind the firewall, under the glare shield where the V tubes come together (on top of the ground tabs). I basically formed three studded tabs using cushioned clamps, some stainless truss head screws, star washers, and standard nuts. You'll have to play with it a bit to figure out how to clock the 20A a few degrees off of 0 with the connectors pointing toward the left wing. Two tube clamps above the ground tabs and one below. Slip the 20A over the studs and fasten down with washers and Nylock style nuts. I wanted the connectors pointing left so that the GPS Coax would run up the left sided of the aircraft instead of the right because I wanted separation from the COM Coax for as little chance of signal interference. Then we used 22g wire for power and ground and 22g shielded twisted pair for RS-232, and made the pinout connections per the G3X install manual. I decided to add the power wire to the transponder circuit breaker since it doesn’t affect the amperage value and because the transponder is not on the IBBS system. The transponder goes off line in the event of an electrical failure anyway and therefore no ADS-B. The 20A is irrelevant at that point with no 1090ES signal.

Settings:
After the install, go to the configuration page of the G3X. Configure the transponder for ADS-B and set the Source Integrity Level (SIL). I will have to post again with the details since I can't recall exactly at the moment.

Testing:
After all this, we did some flight testing to evaluate the VHF Com had not lost any performance and I emailed the FAA for a compliance report. All the testing prove to be a good configuration of components and the FAA said all looked good on the Compliance Report.

As I’m typing here, I got a notification that Chuck has posted to this thread. No doubt he is wondering how this project is coming and wants some details. Hope this helps Guys! I’ll see if I can get some pictures posted and the exact settings as well.



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[marcusadolfsson]

Thanks for the writeup! Sharing breaker with the transponder makes perfect sense, will take the same approach. The GPS 20A location is similar to where I imagined mounting mine.

Regarding adding the canbus connection, adding the GPS 20A to the IBBS should be straightforward but as you pointed out does not add much value at this point.

I have the legacy VHF antenna on the belly, not sure if it is worthwhile relocating it to the turtle with a combo antenna or just add a standalone Garmin antenna...

[ceslaw]

Matt

Thank you for the excellent summary.

Good timing. Mounting the GPS 20 after the boot cowl is in place could be a challenge.

Chuck

[Dickey]

Yes. Pre Boot Cowl will be easier but retro fitting was not as bad as I had anticipated. Once the display is out, the hole that it leaves makes working behind the panel a lot easier. Turning cushion clamps into studded tabs made all the difference too. I find no pleasure in fighting those things so I chose not to.

I would say the least enjoyable part was routing the coax up the door post and down the wing compression strut while avoiding the flap rod movement area. It's doable though.

BE ADVISED if you have turtle deck mounted RAMI antenna - the bolt pattern is different between the RAMI VHF and the Comant Combo. The Comant has a 4 bolt pattern and an extra center hole for the second coax connection. We chose to change out the entire turtle deck for one that was made with the correct hole pattern. If you already have an aluminum deck with the RAMI hole pattern, you can re-drill it with the Comant pattern. Unfortunately, there will still be a bolt hole toward the aft end that is exposed but it can be filled with a truss head screw. Hard to explain here. Photos would help huh.

I highly recommend this configuration with the combo antenna on the turtle deck. I've never liked the "whip" antenna on the belly panel. It's either swinging around under there because the hardware gets loose or the porcelain isolators are breaking when you tighten the hardware. I suggest re-purposing the hole in the belly panel for a CI 105 Blade antenna for ADS-B "In" and going combo VHF/GPS on top. Just my opinion though.

Matt


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[c130jake]

Great...where was this info 6 months ago. I will wait til 2020 and if I am still alive, I will attack this problem then. My next EX will be super awesome.

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[Dickey]

Great...where was this info 6 months ago.

Sorry Jake, I understand your frustration. 6 months ago, no one but Garmin knew the GPS 20A even existed. They didn't announce it till mid July.



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[c130jake]

Maybe in five years there will be a super cheap and easy to install solution. Not holding my breath.

Jake


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[Dickey]

Maybe. Just be glad your not Certified. There is no waiting for cheaper.........it's all expensive .

Oh, and we're just over 4 years out at this point. Just sayin.


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[Cubrath]

For those of us that bought the Executive glass touch earlier this year will CubCrafters be offering an ADS-B retrofit kit?

Thanks

Mike

[marcusadolfsson]

Matt,

Any chance you can post some pictures of the antenna mount and GPS-20A location? I am going to do the install over the holidays.