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Re: [TowerTalk] RG8X rf power levels?

To: Jack - K4WSB <>
Subject: Re: [TowerTalk] RG8X rf power levels?
From: Jim Lux <>
Date: Tue, 19 Feb 2008 07:28:39 -0800
List-post: <">>
Jack - K4WSB wrote:
> At 01:57 AM 2/19/2008, Van K7VS wrote:
>> With a reasonably low swr 2 to 1 or so can RG8X stand that level of power?
>> Van, K7VS

There's quite a few kinds of coax going under the name "RG-8X", so the 
datasheet may or may not help.

Here are the considerations:
1) Melting the dielectric.  The center conductor is pretty small, so 
with a kilowatt, the current might be high enough to get some heating. 
Unfortunately, the dielectric makes a fine thermal insulator.  OTOH, if 
you've run 600W with no problem, then 800W probably isn't going to make 
much difference.  (Does the feed line feel warm?  If you get one of 
those nifty IR thermometers, can you see a temp rise?).

If you've got a short scrap, do a test.  Hook it up to a DC power supply 
that can put out enough current. 1500W rms is about 5.5 A. SWR of 2:1 
implies that the peaks are twice that: 11A.   Run 11A DC and see if it 
melts or gets hot. (1kW = 4.4A, etc.)

2) Dielectric breakdown. On solid dielectric coax (RG-213, even RG-58) 
it takes several tens of kV to breakdown the dielectric.  On foamed 
dielectric, though, the breakdown is much lower voltage.  Still, though, 
I'd expect the connectors to be the limiting thing, not the coax itself.

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