I'm sorry to say, it sounds like you have an EMI issue. If you key the
mic and the sats drop, that's a pretty good indication of at least one
problem.

Upgrading the software to the latest code should go without saying.
Garmin will insist that you do that before they will help you
troubleshoot such an issue. Garmin did make GPS reception improvements
in some later software releases.

O.K., if there is an EMI issue, why does it only affect the Garmin? The
Lowrance and Apollo units were completely unphased by the transmissions
and never lost their lock during the entire test flight (and the
previous 8 years of use). I tested them all side by side. The Garmin sat
bars were hopping all around in straight and level flight while the
older units were stone solid.

Something specific to newer GPS receivers?

Thanks,

Mike