[Lowfer] coil design validation

[Ed Phillips]

WE0H wrote:
> 
> It will still work. Put down plenty of ground radials or just use chicken
> wire to keep the ground losses down a bit.
> 
> Mike>WE0H

	Before going too far with a giant loading coil try calculating the Q of
your antenna capacitance in series with the ground resistance.  For
example, if the capacitance is of the order of 150 pf (typical value
I've measured for a 50 foot TV pushup mast with a bit of top loading),
the reactance at 180 kHz will be about 5900 ohms.  If the effective
ground resistance is 20 ohms (better than anything I've been able to get
here, even with a ground to a 150 foot piece of 2" water pipe), the Q
will be a bit under 300.  So, if you wind a coil with a Q of 300 you'll
lose about half your power.  I've made several loading coils using 5.25"
mailing tube forms and find that about 240 turns of #24 close wound will
be me a bit over 5.2 mh with a Q of about 300.  That's the smallest I'd
go, and costs half an S unit.  I've also made a coil on a 7.5" form
(cardboard tube out of a carpet) close wound with 220 turns of #18.
About the same inductance but measured Q of about 600.  It has a
measured Q of about 600.  That's as far as I'd go unless I liked monster
coils, which I happen to do.  Persuaded my friend Dave Curry (PLI) to
wind a big one with #14 wire (12" form, close wound), which gave a lot
more Q (about 800, as near as I could tell) but not much more signal. 
Lots and lots of work.

	After having said that I suspect that some of the guys with a really
goind counterpoise system will have a lot lower ground resistance and
larger coils are probably indicated.

Ed

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