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post #1 of 12 Old 02-14-2008 Thread Starter
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Loose antenna cable in mast

My antenna cable is banging around inside my mast, very annoying at night, when everything is quiet. I'd like to fix this before someone complains but not sure how. Any suggestion would be appreciated by me and my neighbors.
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post #2 of 12 Old 02-14-2008
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Depends on how much work you want to do. The proper way to do it, would be to pull the wire up and then install a wiring conduit in the mast and run the wire back down the conduit. This would probably be the most work though. It also depends on whether you have internal or external halyards. My friend's boat has internal halyards, and what she ended up doing was pulling the wire up after attaching a messenger line to it...then putting three large cable ties on the wire, pointing 120˚ apart, about every three feet and then pulling the cable back down into the mast. The cable ties act to keep the wire away from the mast, so there's no noise. The cable ties don't seem to interfere with the halyards at all either.

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post #3 of 12 Old 02-14-2008
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How was it secured previously?

Any antenna cable that is hanging unsecured for any length, will self-destruct as the weight of the cable pulls the "stretchy" exterior down faster than the center lead, resulting in the insulation compressing and the electrical characteristics of the cable degraded. (The SWR will increase, your signal will get weaker, usually the radio will not be harmed but it may shut down from the higer SWR eventually.)

Without knowing the the of boat, mast height, deck stepped, etc., it is hard to guess what might help in the interim. We needed to replace one cable FAST for a race and wound up taping it to the outside of the mast for the duration. Butt ugly...but we made the start on time.
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post #4 of 12 Old 02-14-2008
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Maybe you could wrap the antenna cable around the halyards a couple of times inside the mast.

(Just kidding! Don't yell at me!)
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post #5 of 12 Old 02-14-2008
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If you don't want to install a conduit or cable ties, another option would be closed cell foam which will not absorb moisture and which can be placed at various points along it's length. The first two options would seem preferable.


I'm not sold on the elongation myth that coax will deform over it's length if hung vertically. I and many others I know have had multiple similar coax feedlines hanging exposed directly to weather for decades on our ham radio antenna towers with no such deformation. Some of these towers are crank-up design which inherently require the coax to hang and twist. If that claim was true, any coax in a conduit would suffer similar fate and I've never seen or heard any problems. Age and water penetration are the most common reasons for replacement.
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post #6 of 12 Old 02-14-2008
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K1, coax is mainly plastic and if it was rigid--you couldn't bend or coil it. It is designed to be yielding, and the "better" insulators tend to have more air and less plastic in them, making them even weaker.

I think every cable maker, and the ARRL and the other radio organizations, all say that coax must be supported or it will "go taffy" and pull out on itself. For you to call that a MYTH and a lie, just because you haven't noticed a problem with the particular coax you use, is a bit rash. Sure, they could all be lying. But first try this: Buy 100' of premium coax with an airy insulator and thin center conductor. 1/4" stuff like most boaters use, not RG8. Lay it out, use a steel tape to measure and mark two poins 100' apart on it.

Now suspend the top end from something and let it hang unsupported for a year. then lower it, and measure the distance between those two marks once again. THAT will be lab science. And, I'll bet that those 100' marks will be more than 100' apart.
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Please don't take offense. I guess you could also argue that the soft-drawn copper inner conductor will also elongate over time. Hopefully you would agree that the relative deformation, given the elasticity of all the components of coax, is a complex matrix not commonly well studied or even relevent to the issue of loss which wasn't the subject matter.

All I can suggest is that when one considers that virtually all coax in masts, conduit contained or not, suffers equally, I don't think too many of us are overly concerned about deformation as much as how to prevent it from making noise or chafing.
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post #8 of 12 Old 02-14-2008
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HS-

It would also depend on the height of the mast. It might not be a problem in a 30' boat with a 38' mast, but it might be one in a 42' boat with a 65' mast.

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post #9 of 12 Old 02-14-2008
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I've never known elongation to be a problem, but hanging the coax on itself through the mast so that the weight of the cable causes constant, unrelenting pressure at the bend, is. Cold flow will eventually cut the jacket and braid without chafe protection. It's been mentioned that any form of 'chinese finger trap' should bear the weight.
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post #10 of 12 Old 02-14-2008
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None taken or intended. If you look at the way that the military laces wire bundles, or the way that utility cos wrap copper wires with steel tension wires...there seems to be no question that plain copper wire stretches, and coax stretches even more. Whether that stretch is acceptable will depend on how critical the losses are, how stiff the insulator "foam" is, how long the wire run it, how the hanging is done...I'd rather attach the coax to something relatively unstretchable (like a lightweight "zero"stretch synthetic line) and let THAT line take the force of the hanging, if there was no better solution.

Isn't this the reason that dipole wires are often made of copperclad steel wire, instead of plain copper?

Chinese finger traps are great--you're just going to need a "REAL" electricians' supply house to find them.
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