[TowerTalk] C31XR modeling question

[David Gilbert]

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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