No STC required, My instalation is via a Bendix/King mechanical relay that fits into the panel.
The relay disconnects the VHF 2 from its antenna when you plug in the hand held antenna cable. A very minor modification that I did when the rest of The avionics were changed.
At 3000ft it increases the range of the hand held from about 15 miles with the rubber antenna to at least 60 miles ( I did not bother to test it further than 60 miles).
Last edited by A and C; 15th Jul 2012 at 12:27.