I will be installing a Garmin GTX 45R remote transponder behind the panel. This requires a single antenna for both the transponder and ADS-B (in and out). I am using the Comant CI-E05 antenna (experimental version of the Comant CI-105).
The antenna must be at least 3 feet from other antennas, installed on the bottom of the aircraft, and have at least 3 feet of antenna cable. The most suitable location I could determine was in the tunnel, ahead of the spar, and aft of the fuel pumps.
I won’t have fuel filters in the tunnel so I used two of the existing rivets holes as holes for a doubler. I made a 3d printed template to set the hole spacing based on the existing holes.
I then created a doubler from .040 per the template and match-drilled it to the bottom skin. After deburring, I dimpled the doubler and the bottom skin.
I taped off areas around the screw holes for conductivity, then primed the doubler.
The doubler was then riveted to the bottom skin. I used some washers that I had to temporarily attach the antenna but I plan on using larger washers to distribute the load a bit more on the skin.
One more small task completed.