Topband: RF resistance of wire

[Tom Rauch]

> FWIW:  I tested a 1000 foot run of open wire line
> made with STRANDED aluminum 4 AWG THHN wire.  It
> was very low loss, a few tenths of a dB on 160
> up to about a dB on 10 meters.  I would say that
> the stranding didn't cause much harm, based
> on these results.  Just an anecdote.

In amplifier tank circuits at HF carrying high current, braid from RG-
8/U will overheat and melt while #14 tinned buss wire will barely get 
warm. If you simply tin the length of braid making it one conductor 
(of mostly lead) the problem disappears. That's a remarkable 
difference.

The same thing happens in RF relays. Woven armature leads 
overheat and fail at much less current than stranded leads, which 
are not as good as thin flat foil leads.

Stranded wire is much less of a problem that woven or braided wire 
(the more rapid the weave the worse the problem), the effect in 
stranded wire is of one of losing surface area because of both 
proximity and skin effects. When I get some time while doing some 
high-current work, I'll measure the effect and quantify it for various 
wire types.

Lightning is another issue entirely. Braided conductors (and 
stranded conductors) are a very real problem. 

All in all, it is a good idea to not go out of our way to use stranded 
or braided wire. It is never better for anything except when being 
repeatedly flexed. And it is certainly no good when exposed to 
weather or high current/lightning!

73, Tom W8JI
W8JI@contesting.com 



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