Re: [TowerTalk] solid THHN vs jacketed copperweld

[Steve Maki <lists@oakcom.org>]

Thank you. Very interesting. I never ran across on the google what the 
ideal antenna true R should be for the commercial 4 square black boxes. 
Everything seems to assume that one is using a 1/4 wave vertical with 
*some sort of* good ground system.
My modeling skill hadn't progressed enough to confidently figure all 
that out.
I was measuring through a calibrated test line. I was fairly amazed at 
how long the antenna wanted to be a 70 ohm antenna until I got close to 
the 90° *apex* angle at the center insulator.
It kind of jumps to 50 ohms all of a sudden.

-Steve K8LX


On 9/19/2022 6:41 PM, Gary NA6O via TowerTalk wrote:
> Actually 50 ohms (resistance, at resonance) at the feedpoint is perfect. The 
> 1/4-wave, 75-ohm phasing line transforms that to 100 ohms. Then pairs of 
> elements are paralleled to yield 50 ohms. Finally, a 90-degree hybrid combiner 
> drives the two pairs in proper phase.
>
> Difference between the two *insulated* wires should be very small. That assumes the 
> copperweld has at least thick enough copper that it doesn’t start looking like a 
> resistor…
>
> -Gary NA6O
>
> > On Sep 19, 2022, at 2:57 PM, towertalk-request@contesting.com wrote:
> >
> > From: Steve Maki <lists@oakcom.org <mailto:lists@oakcom.org>>
> > Subject: [TowerTalk] solid THHN vs jacketed copperweld
> >
> >
> > Wondering whether there is any substantial difference between #12 solid
> > THHN and #12 PVC jacketed copperweld (steel) in terms of cutting a
> > dipole to length.
> >
> > I'm in the process of installing a K8UR style 80M four square. I trimmed
> > the first element to length using THHN. Then I decided that I should use
> > steel wire for at least the top half of the elements because of the high
> > wire tension I ended up with after pulling the feed-point out far enough
> > from the array center. It's an issue with not enough acreage around the
> > tower.
> >
> > Even so I ended up with a 50 ohm antenna rather than the desired 30-40
> > ohm antenna per the DXE instruction manual. But that's an entirely
> > difference issue (though I'd appreciate any comments on that as well).
> >
> > Should I expect the steel wire lengths to be pretty close to the THHN
> > lengths, or should I re-do the initial step of carefully cutting the
> > first element in isolation?
> >
> > TIA!
> >
> > -Steve K8LX
>
>
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