[Lowfer] Why put a coil under the top hat ???

[Andy - KU4XR]

Greetings all:

A few things I have learned over time; What works for one; may
not work for another, Theory is just that, it works on paper,
but not always in the real world as it did on the paper. 
 ***   AND !!  ***    Don't argue with sucess !!  

Thus my question.

For Base applications only, what is the benefit of putting a
coil directly underneath a top hat ?? 
What value should the coil be in reference to the Inductance 
needed for resonance ( a known value ), and still have a 
tunable coil at the bottom  for changes in the antenna due 
to weather and such ?? 
Weight considerations and wind load; how should the coil be
constructed ?? ie; what form material, wire size, etc.
Is there an optimum placement in the vertical radiator line ??
such as 1/3rd up, 1/2 , 3/4ths , or right at the top hat ??
 ****   Where can I read up on this ? good information, 
multiple websites will have multiple answers and opinions.
I would like some good solid information on the topic.

Thank for replies, and Merry Christmas to everyone ::



Andy - KU4XR - EM75xr - Friendsville, TN.
LOWfer Beacon " XR " @ 185.29866 KHz ( QRSS-60 )
Coordinates:  N:  35* 43' 54" - W:  84* 3' 16"
http://www.myspace.com/beaconxr
http://webpages.charter.net/ku4xr/