Topband: When is coax 'contaminated' beyond use?

[terry burge]

Hi Bob,

The issue I'm faced with is I have 168' to the base of my tower. The Comtek 4-square box is another 64' up the tower. To get to the wattmeter just outside my shack window is perhaps 15-20 more feet. All told, perhaps 252'. In the process of getting the wattmeter where I could read it while checking the dump power I had to use my expensive LMR-400 for part of this. Now I've cut that down to just one 110' piece but I've got other things to do with the good coax. So I found an unused chunk of 9913 and just installed one of my 'new' screw down PL-259 connectors on it. It ohms out fine and I figure once installed my dump power reading should be pretty close to the same as they were. If there is a big drop I'll know the 9913 is 'unusable' but that is simpler than moving the wattmeter from place to place to see how the loss changes. 

I've already recoved one of my two 110' pieces of LMR-400 by buying 125' of RG8X from my favorite ebay source (sage maidens) but it turned out to not quite be long enough. Hence, the need for another piece of coax. (gee, don't I get long winded in my explanations).
But I'm wanting to get back the other 110' LMR-400 which is waisted in this application. So I'm going to try this. I've always wondered just how bad the 9913 really was looking 'black' as it does.

Since having this contaminated 9913/9913 Flex problem I've not bought another piece of it. But old coax should be good for something...maybe.

Terry
KI7M

> On February 3, 2019 at 9:29 PM "Chortek, Robert L." <Robert.Chortek at berliner.com> wrote:
> 
> 
> Hi Terry,
> 
> It seems to me that it ought to be fine to use the coax.   The fact the coax has more loss than non-contaminated coax shouldn’t matter, since the whole point is to dump the wattage as part of the 4 Sq. System.  Using lower loss Coax would only mean more power would get to the dummy load where it would all be dissipated anyway.  Total loss should be the same.  To my way of thinking it should not matter UNLESS the contamination is such that coax acts as an open circuit.
> 
> Others may disagree, but it seems logical to me.  OTOH, if it were me, and I was only using a very short length, I would spend a couple of extra bucks and use good quality components throughout my system.
> 
> 73,
> 
> Bob AA6VB 
> 
> Sent from my iPhone
> 
> > On Feb 3, 2019, at 7:55 PM, terry burge <ki7m at comcast.net> wrote:
> > 
> > Hi Folks,
> > 
> > 
> > A few years back some 9913 I was using apparently got water in the coax. I say this because of fluctuating SWR issues and I noted the shield when cut into was almost 'black'. So for my minor purpose of using spare coax for my dump power on an 80 meter 4-square can some of this coax be used? When I scrap the shield after exposing it with a knife will reveal the shinny copper again so is that sufficient to use some for reading dump power on my wattmeter at the shack? Seems if I try and get readings like what I had with the LMR-400 then it could be used. Coax is so expensive these days I want to use my valuable LMR-400 elsewhere if possible. And having a convenient way of reading dump power is of course important too.
> > 
> > 
> > Terry
> > 
> > KI7M
> > 
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