[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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