Robert asks:
<<Just re-read the installation requirements for the Comat GPS antenna that comes with the new Chelton Pinpoint GADAHRS. It requires an aluminum ground plane and cautions the user to clean and Alodine it for better electrical contact. Sooooo - whaat is the reaal story? >>

The grounding requirement is likely for lightning protection and not  antenna ground plane.  When we were performing the qualification testing on the Pinpoint GPS it was winter so we hung the Comat antenna out a window. The antenna was aligned such that its base was vertical and parallel to a north east facing metal building wall. The antenna was NOT connected to the buildings vertical "ground wall".  Our GPS diagnostic software showed that  all the satellites within the line of site of the antenna had reasonable to excellent signal strength.

If the antenna is mounted on an external surface of a composite airframe then a ground wire that can drain off ESD is a very good idea. Without this the coax cables shield and receiver case must do the job.

I would also point out that handheld GPS receivers do not have a ground plane.

Regards
Brent Regan