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I wanted to install some antennae on the fuselage before fitting the Rollover Bar.

It wouldn’t be too difficult to access the inside of the fuselage with it in place, but easier with it not there!

Of course` you have to have some idea of the avionics plan to know which antennae to fit. Well I know I need a GPS non-WAAS GPS antenna for the G3X. And then a WAAS GPS antenna for a WAAS enabled GPS navigator such as a Garmin GTN 650.

Here in the UK there is not a universal adoption of ADSB in light aviation, since our authority has taken a long time to decide on a future strategy. It will almost certainly be ADSB, but in the meantime lots of third parties have come up with ingenious ways to receive traffic data without the expense of ADSB devices.

Of course this means that there is not one solution which provides traffic data from all the available options. But probably a good option to future proof the installation would be to include ADSB/Mode S reception, and also a FLARM system. FLARM is widely used by gliders and some light aircraft in Europe.

So I have decided to fit an Air-Avionics AT-1 AIR Traffic – Collision Avoidance System which incorporates all these features, and is compatible with Garmin G3X for displaying the traffic. It also has the advantage that it receives any SIL value, not just SIL > 0, and so provides the fullest possible picture of nearby traffic.



An IFR capable Garmin Navigator requires a GA-35 GPS WAAS Antenna, and the G3X will need a GA-56 GPS Antenna.

They need to be mounted on top of the fuselage, and many builders have opted to place them on the turtle deck just being the rear window.

This seemed like a good plan, so I set about making a doubler for the GA-35 (the GA-56 came supplied with one).

Then allowing for a sensible position relative to other rivets etc, I plucked up courage & match drilled into the turtle deck.


And then used a step drill to open up the connector hole.


I used the Close Quarters Dimple Set to dimple the doubler rivet holes.


Final check before riveting.


The GA-35 has attachment screws, so I attached Nutplates to the doubler.

The GA-56 has integral studs, so nutplates weren’t appropriate.



The AT-1 has the option to fit two FLARM antennae, and this is recommended for best reception since FLARM signals are relatively weak.

I eventually opted for two GAV 868’s, as recommended by Air-Avionics for their system.

These are well made and small antennae (they stick out about 7cm)


I made some doublers, ensuring a good ground connection for the connectors.


So where to site them?

The manual recommends more than 1m away from any transponder antenna. Since I plan to mount my transponder antenna in the Vans recommended place, the only option was to find a place halfway down the tail section.

Actually one bulkhead further back would have been good too, but I decided to avoid this area since it would have been too close to the area modified by the Service Bulletin. I thought it best not to add any additional stress in that area!

I did ask Vans about my proposed sites, and they were happy.


Here is the top location.


Same process to locate the doublers.

The rotisserie made it so much easier to reach inside for riveting etc.

Here is the lower FLARM antenna temporarily installed. Actually it just screws on and off.


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