At 10:03 PM 3/10/99 -0500, L. B. Cebik wrote:
>Force 12 has a description of the operative theories behind their
>antennas--if not at their site, then in their main catalog.
>Joe's account of the feed system, often called open-sleeve coupling, about
>covers the case at that end of the antenna. Given the context of a
>multi-band Yagi, the exact spacing used between the fed and the coupled
>driver is able to be modeled but still requires field setting. ...
To LB's excellent comments I would only add this bit of evidence -- I
modeled the C-3 in EZNEC using the actual physical dimensions of each piece
in the antenna, some 57 different "wires." The resulting model tracks very
well with my physical antenna on 10 and 20, as far as feedpoint behavior is
concerned, but shows much less SWR bandwidth on 15 than the real one does.
Incidentally, the model gives right around 6.9 dBi forward gain in free
space on 20 and 15, and 5.6 dBi on 10. This tends to support the notion
that those shorter elements forward of the driven elements are adding
something to the picture, because those 20 and 15 meter figures would be
pretty high for a 2-element short-boom yagi.
73, Pete Smith N4ZR
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