[TowerTalk] Coax Rating

[Bill Coleman]

On 3/1/01 8:57, i4jmy@iol.it at i4jmy@iol.it wrote:

>The reason why an RG8X insn't raccomandable at high power levels is 
>because of a shield that's made of a thin aluminum Foil-Polyester Tape-
>Aluminum Foil and only very few thin copper wires as braid shield.

All the RG-8X I've ever bought has a braid, very similar to RG-58/RG-59.

>The foam dielectric hasn't significant losses and a foam cable of the 
>same size of an RG8X, but with a classic copper braid or a more 
>consistent foil (aluminium or copper), would safely withstand much more 
>than US legal power at 7 MHz, and roughly twice the power of an RG58 
>expecially at 30 MHz and above.

The issue is probably more of having a proper match to the feedline. If 
you are feed a purely resistive 50 ohm load, RG-58 or RG-8X should be 
more than capable of handling the full amatuer legal limit (and then 
some).

However, if you are feeding an antenna with a complex impedance, you'll 
incur higher losses, and there's a chance that the transformed impedance 
could cause a high-voltage point within the coax -- potentially causing a 
breakdown.



Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@arrl.net
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901


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