[TowerTalk] Re: [Towertalk]Coax Suggestion

n8ug@juno.com n8ug@juno.com
Tue, 4 May 1999 01:35:10 -0400

No such thing as a dumb question, Russ, but there are often dumb answers!
Here's one that is pretty well proven out over the years as sound.
The air dielectric - type coaxes are not much more susceptible than most
any coax, since they all have air in them, with very few exceptions
("flooded" buriable types, etc). The water problem is almost always due
to insufficient sealing and aspiration. If there is the slightest pinhole
in the seal or any area, water or water vapor will enter when the ambient
temperature drops suddenly as with a sudden rain on a hot day, causing a
partial vacuum within the coax, wherever there is air. This can be in the
braid area or in the dielectric, where there is unsealed foam or filament
or spacer type construction. The tiny sip will re-occur in every similar
event until the performance of the coax is compromised.
The installer must learn that a hermetic seal is mandatory, from the coax
jacket below the connector to the other side, which means well past the
mating connector until no possible leakage possibility is exposed ( an
unprotected SO239 will allow water to leak along the center conductor,
along threads, and among center conductor or braid strands).
This is not speculation - it is a fact - in well over 10 years of 9913
and our 4XL product line, we have never seen a leak in a properly sealed
installation. Physical punctures are another matter, of course.
In most cases the input end of the coax is within the shack and in normal
indoor humidity conditions, so ingress of air is seldom a problem.
Exceptions, such as the tropics, field day, etc., must be dealt with
according to their severity.
Towertalk archives contain a wealth of sealing solutions well worth
checking before making an expensive and unnerving mistake. The most
common mistakes are the use of plain electrical tape, where the edge of
each lap is a capillary, and the amateur disease - "I'll seal it later,
after I see if it works OK!"
As for recovery, it is possible if done before it reacts with the
conductors, it dries, and metallic salts are deposited in the cable. A
small bottle of dry Nitrogen gas can be bled into the cable through a
hypodermic needle for several days to absorb the water/vapor and take it
out ( assuming that you've made a second pinhole at the other end!).
Resealing the holes and testing the cable for loss under RF power will
measure the success of the job.
Hope this helps -
Press Jones, N8UG, The Wireman, Inc., Landrum, SC, 29356
Sales (800)727-WIRE(9473) or  orders@thewireman.com
Tech help (864)895-4195 or  n8ug@thewireman.com
http://www.thewireman.com  and the WIRELINE bargain page
Our 22nd year!

On Mon, 03 May 1999 18:03:36 -0400 Russ Connors <aa2gs@isoc.net> writes:
>Looking for a suggestion for a good coax type to connect  my KT-34A 
>remote antenna switch. The cable will need to be abt 80 ft. I've used
>4XL but it seems I always end up w/ water in it. I've been reading 
>numerous posts on sealing up the the connector...maybe someone can 
>me the Readers Digest version again...sure some others could use the
>advice. You newbies out there....just wait til there's a contest or 
>DX  and your SWR goes to pot. You diconnect the cable from the 
>turn it up side down and water a gallon of water flow out of it.
>BTW...this brings up another question...Is the coax/water pipe ever
>usable again as a transmission line? Can you dump the water out and
>leave it out in the sun to supposedly dry and be all set??
>Dumb questions but that's as good as I can do right now.

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