RE: [TowerTalk] 8X center migration in a coax choke?

[Jim Lux <jimlux@earthlink.net>]

At 08:08 AM 11/17/2004 -0800, Steve Katz wrote:

> > ::As for solid-dielectric RG8X type cable, Radioworks is now selling
> > precisely that; advertised as "Super RG8X."  This design change obviously
> > violates the original RG8X "spec," it would have to with a solid
> > dielectric.  To maintain 50 Ohms Zo, they'd have to either make the center
> > conductor smaller gauge, or change the cable diameter; not sure which they
> > did, but I'd guess they decreased the center conductor gauge to maintain
> > the same cable O.D. and still hit 50 Ohms.

Wouldn't this then be something like RG-58?  The whole point of RG-8X, as I 
understand it, is that the dielectric is foamed, and, so lower loss, 
particularly at high frequencies.

The impedance of a coaxial line is proportional to 1/epsilon *ln(Router/Rinner)

The dominant loss in HF coax is resistive, and primarily from the center 
conductor, so you'd want to have a bigger center conductor.  This would 
make Router/Rinner a smaller number (and hence, the ln of the ratio 
smaller).  To keep the same impedance, you'd want to make 1/epsilon bigger, 
which means reducing the dielectric constant (epsilon).  RG-8X does this by 
foaming the dielectric (so the overall epsilon is part air(gas) part plastic).



> If so, the "new Super RG8X"
> > probably has a higher DWV (voltage) rating, but may actually have more
> > loss, and a lower power handling ability, since most of the loss in coax
> > is the skin resistance of the center conductor, and if you make that
> > smaller, you're going in the wrong direction.  Anyway, you might want to
> > look into this on the Radioworks website. -WB2WIK/6
> >
> >
> >
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