It seemed to me that the most likely culprit was that last two inches of
unshielded wiring and the unshielded connector...especially since they
were
the closest part of the wiring harness to the transponder.

So, today I took a roll of aluminum foil out to the airplane and wrapped
foil around the back of the radio, leading it down the wires until it
contacted the braid. Duct tape, of course, to hold it in place.

I'm happy to report that this solved the problem. Radio signals were
perfectly clear.

I figure the foil isn't worthwhile as a permanent solution. A guy at the
airport suggested using aluminum window-screen material. It appeals to
the
cheap side of me.

The inside? :-)

You get more flying time per buck than anybody I know. What do you do with
all the money you save?

Ed Wischmeyer