Topband: What wire to use for 'wire' TX antenna
Thu, 26 Jul 2001 08:51:14 -0400
> occurred at 800W)! With the various online antenna
> wire & cable companies advertising "flex-weave" and
> other elaborate wires for 'wire' antennas, what seems
> to work well? Seems like "freedom from kinks" and
> "rugged" might not go together. I suppose I need
> better than 14 gauge; that's what melted! I still
> can't believe I had a current node that high - on a
> physically short antenna?
Woven or braided conductors have a lot more resistance per unit
length than smooth surface conductors. Clean, shiny braid that is
compressed (like the braid inside coax, compressed by the jacket)
has about four times the loss resistance of a smooth conductor the
same size and material. That's why most low loss cables have a
smooth metal foil or solid tubing for a shield, and use solid center
Coax braid, if you look at it, is a gradual weave with strands laying
side by side and yet it still increases loss.
If you remove pressure from the weave, RG-8/U size braiding has
about the same resistance per foot as #14 or 16 solid copper wire
on 30 MHz.
When that braid is exposed to weather or moisture and tarnishes,
the RF resistance really increases. As a matter of fact that is
almost the entire reason wet coax gets so lossy...and why it
doesn't recover even after it drys out inside!
The denser the weave, the poorer the conductor at RF and the
quicker corrosion will make the resistance increase even more.
How much this matters depends on how much current flows in the
conductor. It might not matter in some antennas and in others it
could easily be a show-stopper. It certainly is bad news for
73, Tom W8JI
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