Bought a homebuilt once. Both radio antennas had been installed the same
way - with the cardboard drilling pattern glued to the aluminum - then
left
there, and the antenna installed over the top of it. No ground plane.


The SWR was OK (1.8:1), believe it or not. It worked out to 10 miles
or
so - then things started getting weak and scratchy.

Both radios are mounted to aluminum rails bolted to fuselage longerons
however each radio has an aditional grounding wire (from it's main
plug) to fuselage as a precaution. The SWRs also check out the same as
you discribe as does the performance. Power output does not seem to be
the issue (again I never checked power output in the winter), just
audio quality.

Jim