[TowerTalk] Loss of wet RG-213

[Roger (K8RI) on TT]

On 3/31/2015 3:52 AM, Markku Oksanen wrote:

I would not expect the loss in the cable to rise much, but that's with 
several caveats.  Depending on the dielectric what it is made of and if 
foam the cell structure as well.  That and the composition of the rain 
water.  Gone are the days of nice, pure, soft rain water...at least if 
you are down wind from an industrialized area and that's up yo 300 or 
400 mile (or even more depending on the industry and winds)

BUT I would expect a rapid deterioration of the braid/shield.  Al foil 
will fail even faster.  Also the UHF connectors  are locations where the 
water can collect.  Today's rain water is likely to have a low PH. 
Possibly very low.  That would lead to high loss at the connector and 
very rapid deterioration of solder, braid and even the dielectric 
depending on the dielectric's composition.

There are just too many possibilities to calculate an expected loss. It 
can be a little or with today's acid rain it can be a lot accompanied by 
rapid failure of the coax itself.  If you are in an area where acid rain 
is prevalent, it would be best to write it off and replace the coax as 
it's likely to fail fairly soon.  Give it a few weeks and copper braid 
will turn black. That oxide can form thousands of tiny diodes.

No, you don't need hardline, or a professional installation.  You do 
need to study the proper installation of connectors and water proofing.  
A properly waterproofed UHF connector is fine, but, There is always a 
risk associated with depending on water proofing.  The old, "If you 
water proof it properly, then you will have no problems" is a myth!  It 
will likely extend the life of the coax, but you are playing the odds.  
I used to believe that myth, until my system took a direct hit that 
removed all of the water proofing and silver plating at the top of the 
tower  on a 200 ft plus run of 9913.  15 minutes later I had water 
running out of the 2-meter rig and onto the desk.  T found the water 
proofing in the back yard, looking a lot like expanded metal.

There are a number of good water proofing methods.  I like the simple, 
"flooded"  heat shrinkable tubing.  Some dislike that, or any method 
that leaves gunk on the connector.  Me?  I take the, It may look crappy, 
but doesn't hurt the function of the connector, either mechanically or 
electrically and they can be water proofed just as good as a new one.  I 
like the idea of it all being bonded together as it adds mechanical 
strength to the connection and reduces the stress on the braid so it's 
not trying to pull out of the connector.  It bonds the coax jacket on 
both sides of the connection together which is usually a weak point with 
UHF connectors.

73

Roger (K8RI)





> All
> We had a very rainy fall last year and I noticed a signs of water at an UHF connector.  The cable runs some 150 feet up the tower and  and the water must have been coming along the cable.NOW I have been trying to find definitive numbers of estimated loss for a wet RG-213 at, say 28.5 MHZ.  For some reason, no luck on the internet anyway.  Although I intent to change the cable, I would like to know what this does for the time being.
> Thanks for the help!
> MarkkuOH2RA/OG2A/WW1C
>
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-- 

73

Roger (K8RI)


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