Gary wrote,

A flat coil should work fine as a capacitance hat.

I have thought about trying this. With a spiral or flat coil you have a hat
and a loading coil all rolled up in one. Winding spiral coils is not easy,
and
the mechanics of mounting on my mobile antenna have kept me from trying, but
I
may yet. What do you think Tom?
73 Gary N4AST


Hi Gary,
it may not be worth all the work involved. I'm not an expert on
mobile antennas, so don't take anything I write on the subject too seriously.
On the other hand, there should be some current into the coil causing a
changing charge density at the other end which would, in turn, cause a
changing electric field in the vicinity of the antenna, which would cause
electromagnetic radiation, so you might see some improvement over
what you're using now, after all.
Try it out.
73,
Tom Donaly, KA6RUH