RadioBanter - View Single Post - Dual-Z0 Stubs

Richard Clark · May 11th 09, 11:19 PM posted to rec.radio.amateur.antenna

On Mon, 11 May 2009 14:09:29 -0700 (PDT), wrote:

Hi Richard,

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

Hi Steve,

That's OK. Even the Corums didn't answer them and it accounts for the
rather thin material being leveraged into the new-age science we get
discussed here.

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".

It is only a "red herring" if you were intent on mischief. If you
were, you are surrounded by accolytes better versed than you.

However, silly or otherwise, it doesn't answer the intent of the
question. The coil size doesn't change by segment count, but by wire
count, diameter, turns per inch, length. If any of those changed
along with number of segments, then you haven't really done anything
but compared two arbitrary designs to discover they don't match.

What profit in that? (and why did we branch the topic?)

Or they do!

What is to be learnt that this illustrates? (and why did we branch
the topic?)

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.

That is an objection, not a reason, and very far from a discipline
(Corum vs. the world).

What I asked is, if you use Corum (against its provisos) to obtain a
value (fully acknowledged to be erroneous when the provisos are met,
they aren't), for applications that contain considerations that the
Corums do not contemplate, AND you use another tool to validate the
answer - why is it that you wonder on the happenstance of correlation?
This puzzlement is enough to suggest Corum may bring grief
unexpectedly. Does this make the muddy prospects of its utility
clearer?

Still and all, this side-topic is still stuck at the gate to your
buying the farm. Skip the coyness by subscribing to Corum and let
Cecil introduce you to new vistas where these missing degrees will
suddenly emerge again. When that happens, all that is required is
that you suspend your doubt that if that coil at the base of a fixed
height antenna were moved, it would fulfill resonating that fixed
height antenna with the same number of Corum "electrical degrees" in
migration. If Corum "electrical degrees" have to be augmented with
appended theory (diluting the original's importance to elevate the
appendix, as it were); then I would ask again: Does this make the
muddy prospects of its utility clearer?

Yes, Steve, I can full well appreciate that you wouldn't necessarily
expect the same coil to resonate the same, short antenna every where
you happened to place that coil along its fixed length. But this
side-thread isn't going to get any traction until you go with Cecil's
flow (which will undoubtedly swirl into another stagnation at this
point of my observation).

73's
Richard Clark, KB7QHC