My Optibeam OB16-3 tribander has a similar feed method for the three
bands (one feedline) using some square tubing. It functions as a
transmission line, so I calculated the characteristic impedance of the
transmission line based upon the diameter of the square tubing and the
spacing between them (formulas for square conductors exist online) and
then used that figure for two appropriate lengths of transmission line
connecting the three feed points in EZNEC+ to model the antenna. I got
results for both pattern and SWR curve on all three bands essentially
identical to the ones published by Optibeam.
It worked for me.
73,
Dave AB7E
On 5/19/2019 3:51 PM, jimlux wrote:
On 5/19/19 3:29 PM, Tom Hellem wrote:
Has anyone ever tried to model in EZNEC a C31XR tribander, the one
sold by
JK ?
I would specifically like to know how to model the feed system which
consists of two pieces of aluminum angle that connects the feed
terminals
of the 3 driven elements.
Since they advertise modeled patterns on the website, have you asked
JK for their model files?
I don't know if they're advertising gain in QST, for which they'd have
either model files supplied to ARRL, or measured data.
I didn't see this antenna listed here
http://www.arrl.org/antenna-modeling-files
In general, you should be able to model it as a wire connecting the
appropriate points. Set the wire diameter so that the surface area of
the wire is the same as the mounting bracket's. That way the skin
effect losses work out the same.
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