FWIW

A coil will always lower the power handling ability of an
antenna. Large coils lower it less than small coils, but both
large or small coils lower the antenna's power rating. That's
because of the resistance of the coil. A fact of life, get used
to it, it won't change.

A coil's efficiency is directly related to it's size. Big
coils are more efficient than smaller coils. A coil's
efficiency
has nothing to do with how well it 'radiates', unless the coil
is an appreciable fraction of a wave length, it radiates no
better
than a length of wire of the same length. Longer coils radiate
better than shorter coils, but neither radiate enough to make
any
practical difference.

A coil's 'Q' (another name for efficiency) is indirectly
related
to how 'broadbanded' an antenna using that coil is. If the coil
has
a high 'Q', the antenna will be less 'broadbanded' than an
antenna
using a coil with a low 'Q'. A dummy load has a very low 'Q'
and it
is very broadbanded. A high 'Q' antenna is very narrow banded.
That's
another one of those facts of life, and physics.

An antenna advertised as being high 'Q', and being very
broadbanded
is 'advertising-physics', in other words 'B.S.', in the purest
sense of
the term. If an antenna manufacturer want's me to believe that,
it makes
me wonder what other 'B.S.' he want's me to believe...

There are no secrets or magic about how antennas work. It's
all physics,
it's all documented by people a lot smarter than you or me.
It's there, all
you have to do it read it.
'Doc