Two soggy Heliax lines!

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Two soggy Heliax lines!

Post by k4pdm » Wed Aug 01, 2018 4:08 am

Hi everyone, new to the forum.
We have an 1 5/8 inch cable in which water has been accumulating for a couple of months due to management inaction when a major leak was discovered. The cable has been drained at the base of the tower but there is still high SWR after a few days.
The holes have been patched. Will this line ever finish drying out on its own?

Then, early this morning, one of our co-located stations shut down due to high SWR. This line would lose pressurization over time, but very slowly. I am assuming this 3 1/8 line has water in it as well. It is on a dehydrator shared with three other lines. Will it help it stay pressurized if I turn the air off to the other three? Will it ever dry out on its own?

I've been at this game for a long time but this is my first real experience with water in the cables.

There was a major lightning hit on this tower about a month ago, by the way.


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Dale H. Cook
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Re: Two soggy Heliax lines!

Post by Dale H. Cook » Wed Aug 01, 2018 7:15 am

You may well have to replace both lines. If you put power to a line that has water in it that can easily cause damage which is not correctable.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA

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Re: Two soggy Heliax lines!

Post by RGORJANCE » Wed Aug 01, 2018 8:00 am

I have seen this many times over the years. In the ones I have seen, most were the result of lightning strikes. Some caused by bullets (from guns). The lightning not only can put a hole in the line, but introduces carbon deposits. That stuff migrates and will make a huge length of line useless.

Only way to tell for sure of the condition of the line is to sweep it. That will show the condition---good and bad as well as the extent.

Two types of equipment are useful.....infrared photography will show the hot spots, where a line analyzer shows the detailed internal condition.


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Re: Two soggy Heliax lines!

Post by Kelly » Wed Aug 01, 2018 8:22 am

"Draining" lines is a very temporary solution while waiting for the new line and tower crew to replace it. There is no way the line will ever dry out, and as mentioned, carbon and corrosion will cause heating and increasingly poor connections at the antenna. Replacement is the only option.
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Deep Thought
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Re: Two soggy Heliax lines!

Post by Deep Thought » Wed Aug 01, 2018 10:45 am

The inside of that line is almost certainly corroded and full of carbonized crap at this point. As noted above, this is a replace, not a repair.
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Re: Two soggy Heliax lines!

Post by Lee_Wheeler » Wed Aug 01, 2018 5:18 pm

The line that has been pressurized shouldn't have any water in it even if there is an air leak. So long as there is any positive pressure that will hold on the line water cannot get into it. On that line I would look elsewhere for the problem.

The foam line will likely never return to normal if it was waterlogged. It might get better over time but never again will it be great.

I have been called in on half a dozen bad lines over the last several years and, in nearly all cases, it was due to the outer conductor being sliced when the ground kits were installed. The copper on the newer lines is less than paper thin and, even if the line looked good when originally installed, the line grows and shrinks with temperature variations and it ultimately separates if it was significantly sliced when installed.

Make sure to impress on the tower crew that replaces the line(s) to be very careful when they install the ground kits.


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Re: Two soggy Heliax lines!

Post by k4pdm » Thu Aug 02, 2018 4:09 am

Thanks, everyone.
Looks like we are in for quite some expense.

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Re: Two soggy Heliax lines!

Post by kkiddkkidd » Thu Aug 02, 2018 7:02 pm

And don't forget that a lightning strike can physically and electrically damage the antenna itself. It can crack/burn the antenna tubing which will allow water to enter as well as trash various important internal parts.
Kevin C. Kidd CSRE/AMD
AM Ground Systems Company
KK Broadcast Engineering

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