Owen Duffy wrote in
:

....
I have been quiet here, but have been modelling and writing notes up
on the results. I have asked for comment on a draft model, and subject
to that, I will post the URL for further comments, hopefully in a day
or two.

http://www.vk1od.net/antenna/ccps/index.htm

Owen

On Tue, 31 Mar 2009 20:13:36 GMT, Owen Duffy wrote:

Owen Duffy wrote in
:

...
I have been quiet here, but have been modelling and writing notes up
on the results. I have asked for comment on a draft model, and subject
to that, I will post the URL for further comments, hopefully in a day
or two.

http://www.vk1od.net/antenna/ccps/index.htm

Owen

Hi Owen,

This is a lot to digest at this time, but at least it is all in one
place and done well.

You offer several many solutions (to what are arguably straw men
hypothesis such as the W5GI mystery antenna) and there are certainly
gaps that beg filling: Fig. 2 is rather anemic as is the original
supporting commentary.

I offered a comment long ago that my best guess was that phasing would
seem to separate your two examples. That seems to have been both
vindicated and rejected through the numerous examples - I've lost
track of the focus.

I will have to revisit the comments in this thread and tie them to the
cogent points of your page.

73's
Richard Clark, KB7QHC

Richard Clark wrote in
:

Richard,

If it doesn't come through on an initial read, I have tried to deconstruct
the fig a) / Fig 1 configuration, and then synthesise it with another
structure with and without the common mode current path, and observe the
effect on current distribution... then compare that with the TL
representation.

If the development isn't clear, I have some more work to do!

....
I will have to revisit the comments in this thread and tie them to the
cogent points of your page.

Constructive comments are always welcome, and appreciated.

Thanks
Owen

On Tue, 31 Mar 2009 22:27:57 GMT, Owen Duffy wrote:

I will have to revisit the comments in this thread and tie them to the
cogent points of your page.

Constructive comments are always welcome, and appreciated.

Hi Owen,

I can well appreciate the issue of common mode driven by coupling to
the field. The work-arounds I would have expected Roy to have offered
would have been a combination of the TL faculty of NEC for the
differential mode, and an appendix-like wire to support the common
mode contribution. The lack of this discussion where it often appears
in other threads leaves me to wonder if other issues are being
discussed here; hence my problem with topic focus.

As for the modeling of a coaxial transmission line by wires, I have
fairly convinced myself that that approach is thoroughly dead (having
seen no contrary response to my comment about the concept of a Faraday
Shield being unknown to NEC).

By these two, it would seem that modeling coaxial components in NEC is
intractable and claims applied to their use will only be
proven/disproven in the lab or the field.

Proceeding from this last conclusion, I cannot see any purpose to the
comparison of the two colinear representations. You certainly bring
many issues to bear, but except for vague references that are 60 years
old, I don't see any solution to your original questions (which is
where I thought the focus resided).

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Tue, 31 Mar 2009 22:27:57 GMT, Owen Duffy wrote:


By these two, it would seem that modeling coaxial components in NEC is
intractable and claims applied to their use will only be
proven/disproven in the lab or the field.


Depends on what you want to do with modeling coaxial components. A wire
to represent the (radiating)outside, and an appropriate NT or TL to
represent the (non radiating) inside works fairly well.

If you actually want to model the cable itself (including the fields
inside), I suspect it won't work so well. MoM codes in general often
don't deal with modeling the fields inside closed boxes very well.

I suspect that the cases where it doesn't are basically in the category
of things that MoM codes don't do well with in general, and you need to
go to a different kind of model (FDTD? etc.)