On Nov 3, 1:54 pm, "John Doe" wrote:
If you can't contribute anything positive to this question, then stay out of
it, with your trash!

I have a 10m base loaded mag mount antenna, that I had to put a piece of
felt over the magnet as not to scratch a new vehicle.

When I did this I apparently changed the capacitance between the mag mount
and the roof of the vehicle. Someone suggested that I might want to replace
the felt with either a large balloon or a large prophylactic as it is
thinner and the capacitance would then return to almost where it should be.

Positive comments only!

Just use a very thin piece of plastic. Some companies that make mag-
mounts sell circular pieces with adhesive to stick to the antenna
base. But you can just cut out a disk from a zip-lock bag and put
underneath the magnet. It won't slip around.
The thicker the material, the more it affects the performance because
it reduces the capacitance to the metal that the antenna is placed on.
Thinner is better here.
By the way, someone told me to try felt years ago, and I did. The
antenna had more tendency to slip around, and it DID mar the paint on
my car, more than if I hadn't used anything.
Last comment: a balloon would probably get water in it, and keep the
antenna base wet for a long time after it rains (at least here in
Portland where I live!) Not a great idea. And balloons aren't known
for their tougness.
Gary