On Feb 24, 3:36*pm, Cecil Moore wrote:
On Feb 24, 5:21*pm, Owen Duffy wrote:

... mainly because the effective RF resistance of the braid is not easy to estimate.

Is there no data for the RF resistance of the center conductor vs the
RF resistance for the braid? One would think it could be ascertained
by comparing known coax losses to known parallel line losses when the
wires are the same size.
--
73, Cecil, w5dxp.com

There was an article published maybe 15 years ago (RF Design
magazine?? Electronics Design?? EDN??), authored by a fellow from
Andrew as I recall, about some of the finer points of coaxial cable.
I thought it was quite a good article. He had "rules of thumb" for
loss in stranded center conductors versus solid that I remember for
sure, and perhaps for braid as well--I don't recall that for certain.
It wasn't huge, just a few percent, for the stranded center. Of
course in coax, since there's a lot more surface area to the outer
conductor than the inner, the braid would have to be considerably
worse than a solid conductor to significantly add to the total series
RF resistance, so it wouldn't be trivial to resolve by measuring coax
with a solid outer versus a braided outer. You'd have to go to
considerable effort to keep the rest of the construction identical to
nail down the contribution of the braid versus solid outer.

In any event, it seems a reasonable way to get a large diameter RF
conductor that remains flexible...I'd be very surprised if a 5mm
diameter coax braid was a worse two-wire line conductor than 2.5mm
solid, smooth copper. I would want to keep the jacket on it, sealed
against weather at the ends, to keep the copper clean.

Cheers,
Tom