Thank you Charles, for the detailed explanation(s). I found them enlightening. Your reference to EMI bears repeating as we need to understand the principles of electromagnetic radiation in order to build electrically "quiet" airplanes. Know how to make an antenna and then don't do that when you wire your airplane.

Regarding COM antennas and ground plane configurations, if I may summarize:

Antenna on glass epoxy airplane without a ground plane--- BAD
Antenna on carbon epoxy airplane without a ground plane---  POOR
Antenna on carbon epoxy airplane with a ground plane inside---  OK
Antenna on carbon epoxy airplane with a ground plane outside---  BEST

This theoretical ranking is supported by anecdotal reports but a quantitative analysis will have to wait for testing.

Regards
Brent Regan