Mark, Most transponders have a heat sink built into the rear of the case where the high power transmitter is located. The mounting bracket will have a small tube for attaching a small air duct to provide some cooling for the heat sink. The transmitter may be happier with a little cooling air at that location.
For antenna location, don't neglect the shielding effects of carbon fiber on radio transmission and reception. Fiberglass and lumber are non-conductors and not issues for that. Keeping the belly clean is a good thing. Aside from cosmetics, the oil slick will have carbon and lead contaminates, which are conductive. Shielding for the transponder antenna could still become a problem. Sid Wood Tri-gear KR-2 N6242 getting close Mechanicsville, MD, USA smw...@md.metrocast.net ++++++++++++++++++++++++++++++++++ One really dumb thing I did was locate my transponder antenna on the bottom of my plane. I'm not sure what I was thinking there, as it just hangs out in the breeze collecting oil and exhaust, and it could be just as easily mounted INSIDE the fuselage and work just fine. It is possible for oil on the antenna to change the characteristics such that the antenna is not as well matched to the transponder (SWR), degrading performance and potentially damaging the transponder. At least that's what a local EE and avionics whiz told me after my first transponder mysteriously croaked. Inside the fuselage makes a lot more sense, and that's where I put it this afternoon. It took about 15 minutes to move it. Mark Langford N56ML "at" hiwaay.net website at http://www.N56ML.com -------------------------------------------------------- Oh, and a corollary to the transponder antenna thing is don't turn on a transponder without an antenna attached, and definitely don't push the ident button without an antenna. The 200 watt pulse can kill the transponder if it has no place to go, but a long ident blast is really asking for trouble... Mark Langford N56ML "at" hiwaay.net website at http://www.N56ML.com --------------------------------------------------------
