----- Original Message -----
From: "Alan Melia" <[email protected]>
To: "LF-Group" <[email protected]>
Sent: Wednesday, November 20, 2002 10:32 AM
Subject: LF: re Spiral
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]
Hi Alan and Steve,
If I can put my bit in here I think that the spiral top load will be a nice
low loss inductor but as Alan says, in itself it will not "see" much ground.
Rrad depends on the height of the vert. section so it will not increase, The
great advantage of the spiral will be to increase the potential of whatever
top wire you can manage to get up,making it more effective,but as I have
said boringly so many times, the more the better,its the "foot print" that
matters and the worse the ground the bigger the foot print needs to be"Wire
in the air has 100 times more worth than wire in the air " There I've said
it again sorry.
73 Laurie .
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