Topband: Modelling/calculating the radiation efficiency of shortverticals with a capacity hat plus whip?

[Richard (Rick) Karlquist]

> Can anyone give me some help in arriving at the change in radiation
> resistance (efficiency) for a 40 foot vertical on 1.8MHz with a 
> top capacity
> hat 20 feet in diameter with 8 radial arms that then has a 30 foot "whip"
> placed above the capacity hat?
 
When a top hat becomes a "middle hat", it just makes the center of the
antenna look fatter, which is bad for the current distribution.  If
you add the whip, lose the hat.

Rick N6RK