Hi Richard,

I wont even attempt to answer the "intimidating" questions - they're
far too tough for me!

But just a couple of comments:

1) The change in coil size when I swapped from a base-loaded to a mid-
loaded model was nothing more than a convenience to reduce the total
number of segments and reduce the computation time. It was not borne
out of any electrical considerations, so please don't read anything
more than that into it. In retrospect it was a silly thing to do
because it has probably introduced a "red herring".

2) You suggest that the Corum method has little utility. However, the
inductance calculator based on the method appears to give usefully
accurate predictions of "equivalent lumped reactance" and SRF (jury
still out on that one). If that calculator was not available, it seems
to me that designing a coil for something like a mobile whip loading
application would require tedious iterations of the helix generator in
EZNEC.

73,
Steve G3TXQ



On May 11, 9:19*pm, Richard Clark wrote:

Hi Steve,

I don't often drop into this side-thread as the topic had drifted into
a stagnated intellectual backwater.

On this and one prior posting by you:

On Sat, 9 May 2009 13:56:31 -0700 (PDT), wrote:
OK, I tried what you suggested. I put my loading coil midway up a 20ft
vertical wire in the EZNEC model. I reduced the number of turns to
lift the resonant frequency to 5.6MHz.

I note how little Corrum really has to offer when you had to take the
same:effective electrical length of the coil (38.83 degrees)

and change it (to the same effective electrical length? *I think not.)
to fit the same available wire, at the same specific frequency - only
at a different height along the available wire.

By my quick read on the stale crisis of current "fall-off" and proving
Corum by EZNEC; it seems quite apparent that EZNEC (the authority) is
driving the coil requirements which are then force fitted by Corum's
inappropriate application.

After all, Corum says nothing of:
1. *Application;
2. *Base loading;
3. *Mid or Top loading;
4. *Stinger selection;
and yet all solutions seem to derive from their math with the elegance
of an ad-hoc "missing degrees" provision (that is quickly discarded as
shown above when current becomes the focus).

Corum DOES say that the formula is only applicable for certain
constraints which I note are NEVER observed in the application nor the
breach. *All of the commentary proceeds through equation (32) when
every argument is an instance of equation (31).

How much are you willing to accept of that paper (which is another way
of asking how much you are willing to discard)?

I will ask one ace-buster question that I expect no one will answer:
* * * * Show me the computation for M (= tau · a)
which would be appropriate for the NON-quarterwave resonance of the
coil in question at 3.85 MHz.

For extra credit:
1. *What is the wave number, k for 3.85 MHz?
2. *What is the phase velocity for the original (not changed) coil?
3. *What is tau for the original (not changed) coil at 3.85 MHz?

Yes, this is intimidating to ask; but seeing there are so many
authorities on Corum; and that these considerations would have been
done by the authors themselves; then their solutions must reside
somewhere in notes or as marginalia for quick reporting (or could be
summoned up through running through the same math as before).

73's
Richard Clark, KB7QHC