On Thursday, February 13, 2014 4:09:53 AM UTC-6, gareth wrote:

My reasoning is that because the waves spread out in all directions

in the hat, then there is no, or very little, radiation from the hat because

of field cancellation, but when the waves all return simultaneously to the

main element, they have incurred a phase change that you'd get had there

been a capacitor in circuit?



(Always willing to learn more, and to be corrected if my thought

experiment has gone up a blind alley, or in this case, a capacity hat

alley!)

The use of the hat has two main purposes.

#1, it will reduce the number of turns needed with the loading
coil, assuming the whip is shorter than 1/4 wave including the
hat.

#2, and probably most important. It improves the current
distribution through the length of the whip and makes the current
distribution a good bit more linear from the base to the tip.

I don't use one myself, because they catch a lot of wind, and
they look ugly on a vehicle. :/
I compromise by mounting the loading coil as high as possible,
which also helps current distribution.