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.
Sent from my iPad using Tapatalk