[TowerTalk] solid THHN vs jacketed copperweld

Grant Saviers grants2 at pacbell.net
Tue Sep 20 13:10:09 EDT 2022


The dielectric loading of insulation makes the wire electrically longer 
for RF.  EZNEC can model it, if you know the dielectric constant 
(usually around 3 for PVC, nylon) and thickness.

The height of the dipole has a larger effect.  Plus for 160 & 80 quality 
copperweld is needed with thick copper, so the internal field (skin 
depth) is in the copper, not in the steel which will cause high losses.

Grant KZ1W

On 9/19/2022 14:56, Steve Maki wrote:
> 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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