Thanks for your reply Mark,
Will continue to "look somwhere else" but, aside from the fact that we've done many of the other fixes, this one test seems definative that we're dealing with RFI from the engine over the airwaves (and our avionics tech agrees it is):
We have our panel mounted Microair tranciever powered OFF.
We run up the engine on the ground, going up from 2000 RPM to 4000 (the highest I care to run it with the plane stationary with brakes on.)
Our Avionics guy stands about 12 feet to the side with a good ICOM handheld and does test transmissions. As the engine RPM goes out his transmittions get proportionally worse and worse and with more noise in them.
Clearly this can have nothing to do with groud loops or poor wiring in our panel mounted Microair as it isn't even on. It also has nothing to do with our cockpit PTT button and circuit as we're of curse not using it.
As to your question "If you think of all the other aircraft that are flying with the radio within a foot of the engine ignition system and they don't have a problem, why should your engine be different?":
For one, I'm told that Rotax 912's have a particularly high energy ignition system.
Also, many aircraft have metal cowlings which, unlike our fiberglass one, trap RFI inside the cowling.
Also, perhaps we have old ignition wiring which leaks more.
Don't know. Fact is, we appear to be getting RFI over the airwaves out of the engine even when our radio is switched off.
Al
