[TowerTalk] Tips for Modelling swaged antenna tubing sections

[jimlux]

On 9/29/20 1:24 PM, john at kk9a.com wrote:
> With NEC2 I avoid using short wires. If I had a swedged element I would 
> use the length of the unswedge portion of the larger tube and for the 
> next wire I would just add the length of the swedge portion of this tube 
> to the smaller tube that fits inside it. The 1/8 difference in diameter 
> for the small overlapping area should not make a difference on HF and I 
> feel that the segments are more equal and that the model will be 
> reasonably accurate.  Does NEC4 model short segments more accurately?

Yes, there's an improved basis function for the fields along the segment 
so it models short segs more accurately.  That said, I'd model it as 3 
segments: tube from center, slightly larger diameter for overlap, 
skinnier tube continuing out.



> 
> John KK9A
> 
> 
> 
> jimlux wrote:
> 
> but does the model actually show much difference? One can get way down
> in the weeds with this - put a tapered segment in that's 1 cm long, etc.
> But if the wavelength is 20 meters, a 1 cm transition is 0.0005
> wavelength.  I'd worry more about numerical instability than model
> accuracy at that point.
> 
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