In some situations it is better to have a 'shortened' antenna than the
absolute last tiniest fraction of a db. I realize a cap hat can
reduce the size of a vertical with reasonably low loss, I am wondering
if it would do as well with the J-Pole?

For example, a quarter wave matching network for the J-Pole would be
whatever works best, be it original design or some form of balun, but
the 1/2 wave vertical might be reduced in size by forming a capacity
hat above it.

How well would that work for shortening a J-Pole? would it be better
to use a shortened 1/2 wave dipole or would the J-Pole design be
better?

Buck

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73 for now
Buck
N4PGW