Hi Steve, that sounds quite a beastie. we only got to 700 or so uH.....1.4mH
top load sounds very interesting. I think the problem is that you will not
get any help from "analysis" as most of the theoretical treatments dont seem
to be able to deal with inductive top-load and the effect of increased
top-capacitance on ground loss. My guess is that you will not see much more
increase in Rrad now, but I cant judge what effect further development will
have on the ground loss.

You are certainly going the right way to judge from our experiments.  The
problem on ground loss is that the foot-print (as Laurie would call it) is
defined by the sillouette of the spiral so doesnt really increase with the
amount of wire used.  Our ground loss only started to decrease when we put
top-load wires out from the apex above the spiral but then "covering new
ground". I suspect you will have to get the best you can with ground wires
("radials") probably earthed at the ends, like woulld be needed for a true
vertical.  You obviously will not need much inductance at the bottom to tune
up to resonance. Are you able to make any measurements on the structure yet
??

This is a very interesting project.

Cheers de Alan G3NYK
[email protected]