Hi Ian,

Well transmit from one side obviously favors that side and the opposite side of the cockpit will block signals. Hopefully any other Flarm in that sector will alert you, but yes, the other aircraft might not be receiving you.

I was following an ASW-28 a few years ago when I had a single antenna on my glareshield and didn't see him until we turned into a thermal.

Not too long after we both got an alarm and I decided to rework my antenna placement.

Unfortunately while the Flarm website advertised the Core 1.1 could transmit on both antennas, Flarm did not bother to get their FCC and "Innovation" Canada approvals amended to allow that to happen in North America.

Getting a sufficient (thick) coax to the fin is likely impractical. You can't have improperly secured coax interfering with the elevator linkage and the coax would have to negotiate the transition from the fuselage to the fin.

Maybe buy a wreck where the necessary openings have mostly been made.