On May 11, 4:42 pm, Owen Duffy wrote:
I am modelling a Double Bazooka constructed of RG58C/U, and am interested
in a method of estimating the effective RF resistance of the outer of the
outer conductor compared to a round copper conductor of the same diameter.

The structure loss calculated by NEC-2 is about 2%, so it is a fairly small
quantity.

The model so far is of a Double Bazooka resonant at 3.6MHz at 10m height
over average ground, constructed entirely of Belden 8262 (RG58C/U), and fed
with 25m of the same line. The model ignores the effect of the jacket on
the radiator, and assumed that it is a round copper conductor of the same
diameter as the sheild of the coax. The draft results at athttp://www.vk1od.net/DoubleBazooka/Fig01.gif.

Owen

Hi Owen,

A fellow from Times Microwave, I believe it was, wrote an article that
was published in one of the electronics/RF journals back about ten
years ago, about coax, including loss. He included comments about
braids and stranded conductors, I believe. I went looking for the
article some time after I read it, and never could find it again.
Unfortunately, I also never got a positive response from Times about
it when I asked. But if you trust my memory, you can try a value of
about 7% increase in RF resistance as compared with a smooth round
conductor, for braid. That's at best an estimate, but it probably
doesn't matter all _that_ much for what you are doing. I expect it
depends on the angle of the brading, and to some extent on the
frequency; I believe the 7% is for frequencies whose wavelength was
much longer than the "pitch" of the braid, which clearly would be the
case for your antenna.

Hope this is some help and not too much arm-waving for your purpose.

You could, of course, get an idea by comparing the loss for various
types of coax where the difference is in the outer conductor: braid
vs solid. But because the outer is typically such a small part of the
total loss, the estimate's accuracy would be limited.

Cheers,
Tom