Thanks guys. I found the specs in ARINC 716 and ARINC 750. Max permissible transmit power is 40W, and 25-40W is what appears to be built into most bizjet and larger aircraft. VHF3 is in fact a lower power transmitter, in some configurations it appears to be on the battery backup bus. On the A380, VHF1 antenna is fwd top, VHF2 is fwd bottom, and VHF3 is on the top midship. Antenna placement should really only affect range on the ground.