On Fri, 03 Mar 2006 21:15:19 GMT, "Frank's"
wrote:



Owen, I have done some tentative modelling of the CW; how valid the model
is, I am not sure. I used the "TL" card for the actual coaxial feedline,
and ran a single wire from the antenna feed point to one side of the TL
source segment. The idea was to replicate the coaxial surface current. I
don't think the balun (Isolator) will have any effect on the antenna
performance. I may even have the code saved someplace if anybody is
interested. Why would you not use a calibrated EMC monopole for HF?

Thanks Frank. Some thoughts...

I think they call the thing at the top a matching unit, and it seems
to be a 4:1 transformer, but I have no idea of its common mode
impedance that is relevant to the model.

Similarly the common mode impedance of the lower unit (Isolator) is
relevant to the model, and of course the treatment of the main
feedline (routing, where it is earthed).

The loss in the vertical coax is probably relevant, and not adequately
modelled in NEC.

The loss in the main feedline and ATU are also relevant, and can be
calculated from the feedpoint Z.

If I were building a model, I would be thinking of the assymetric
dipole with the generator at the "upper" feedpoint, a vertical wire to
ground loaded where the matching unit and isolator are located, and
loaded for an underground coax feed (as is the case in this
installation).

But, the model will depend heavily on the common mode impedance of the
two proprietary boxes. Unless someone has measured these, or
calibrated a model, the model results will be of limited value.

Perhaps Roy will comment on the above.

Owen
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