|Subject:||RE: [TowerTalk] 8X center migration in a coax choke?|
|From:||Jim Lux <firstname.lastname@example.org>|
|Date:||Wed, 17 Nov 2004 09:41:53 -0800|
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 > > > _______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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