Mike wrote: >>My occasional jumpy readings are due to a dirty transponder antenna just as I thought. It's right in the line of exhaust and picks up a film of grease over a period of hours - just like the bottom of my fuselage under the wing. <<
Another aspect of a dirty transponder antenna is that the capacitance of the housing changes when it's coated with oil. A very sharp electrical engineer I know, who's also an A&P and does pitot/transponder calibrations for local pilots, says it can damage the transponder transmitter or receiver (I forget which) if it gets significant enough due to reflected power impulses. He's the guy that told me that mine croaked because the power lead had become disconnected and the 200W pulse had no place to go. It was an expensive lesson... Mark Langford ML at N56ML.com see experimental N56ML at www.N56ML.com
