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Thread: Found the antenna, now what?

  1. #1

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    Question Found the antenna, now what?

    OK, I found a Mosley CL-33 that I am going to install on my tower. Before I put it up I want to refurbish it. I live on a sea water front property. I will be opening up every joint cleaning and treating with Penetrox and inspecting the integrity of the trap coil forms and R and R as needed...if needed.

    But I am wondering about the surface of the elements. When Aluminum ages it forms an oxide coating that is protective of the aluminum. Unlike rust, it doesnt continue to get worse. But the coating may increase the surface resistance of the elements. So I am wondering if just leaving it alone is best OR polishing it and painting it with a protective coat of cold galvanizing zinc paint or something else would be a good idea. Penetrox is just zinc filings in a waterproof grease and it works pretty well down here on the coast but would not stick to unprotected surfaces very long.

    I would just as soon not take it back down for a while.

  2. #2
    K7KBN's Avatar
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    I wouldn't worry about the aluminum oxide doing anything to the "surface resistance" of the elements. Think of an HF dipole antenna made with insulated copper wire. Insulation doesn't affect radiation to any practical degree. With aluminum tubing, the oxide that forms can be thought of as insulation. It is somewhat conductive, but not so much as to upset a decent antenna like the CL-33. I'd Penetrox the joints for their full length, test it on all parts of each band at a comfortable working height, and if things seem OK, raise it up.
    73
    Pat K7KBN
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  3. #3

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    Thank you. That was the sort of answer I was expecting. But I have been a ham for 60 years and there are always new products coming out so I thought I would ask. Here on the coast corrosion is a problem and taking a large antenna like the CL-33 down and up again is not to be looked forward to. Luckily I can lower the antenna to an 8'x8' work platform without removing it from the pole by telescoping ,my 80 foot tower/pole to just 40 feet. But its still not something I would look forward to.
    Last edited by jimisbell; Thu 30th May 2019 at 03:12. Reason: sp

  4. #4

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    The coating doesn't have much to do with surface resistance. I agree with K7KBN there. What adding a coating does is change the velocity factor of the conductor (but not enough to be concerned with it). Changing the velocity factor changes the "electrical" length, and that changes the tuning of the element. It really comes down to the thickness of the insulation layer and its dielectric constant. The aluminum oxide layer is far thinner than any coating you might add, but I will disagree with the idea that the aluminum oxide layer is as rugged as most people think. Under normal "inland" conditions, yes, it is very rugged and will prevent further oxidation, and that layer is thin enough not to make a bit of difference with the velocity factor. But......

    I used to build trimaran sailboats with anodized aluminum frames and what we learned very rapidly (as did the wind turbine industry) is that aluminum is FAR more susceptible to saltwater environments than inland environments. Deep pitting occurs rapidly in humid saline conditions. Its almost like the oxide layer just dissolves or isn't even there. A few years and you'll notice. Salt is aluminum's biggest enemy (other than lye for those funny chemists out there) !. I know there is a coating that is used on aluminum skiffs to keep them from rotting away in the ocean and I doubt that the thickness of such coating would make a bit of difference in tuning, I just don't recall the name of it.

    You will be fine for a few years if you focus on protecting the metal joints made of dissimilar metals, but if you want it to last a few decades... best do some research and see what the wind turbine industry did. You can most certainly get away with coating it with just about anything if you have a tuner though... Good luck and enjoy those temperature inversions along the coast. I bet VHF is a blast where you live!

    73!

  5. #5

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    Thanks for those comments. I will look into that dingy coating you referenced.

    I talked to a friend (sailboat rigger) who recommends wiping it down with CorrosionX before putting it up. Says it works on sailboat spreaders.
    Last edited by jimisbell; Thu 30th May 2019 at 20:38. Reason: more info and spelling

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    M0WAO's Avatar
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    73 de Biton - m0wao - echolink 633710
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  7. #7

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    Yes, powder coating is the best, but with three elements about 25' long it isnt practical since an oven that big would be hard to find.....LOL
    Last edited by jimisbell; Sat 1st Jun 2019 at 01:23. Reason: sp

  8. #8

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    After reading the contents of several popular preparations that are for preserving the surface of weather exposed aluminum (mostly grease and zinc) and having the manufacturers say they would only last a year if that long. I have come up with a witches brew of my own that I will try.

    4 oz of Lanolin (to hold things together and stick to the elements)($5)
    4 oz of Zinc powder (to act as an anode to keep away galvanic corrosion)($4)
    4 oz of Ethanol (to thin the mixture so it can be applied with a 1/2" brush)($1)

    The alcohol will be adjusted as needed to get a brushable mixture.

    The Lanolin is what I used on my stainless steel rigging on my ocean going sailboat and it lasted for several years per application.

    I will only wipe clean the elements, NO POLISHING or Sanding so as to not disturb the Al Oxide that will already be there protecting the surface....and to avoid as much work as possible. Then brush on a thin coat of the mixture.

    In theory the alcohol will evaporate quickly leaving the very tenacious Lanolin holding the fine zinc particles to the aluminum surface. The Lanolin will "heal" if it is scratched keeping the coverage. What the sea gulls will do to it.....I haven't a clue.

    Hey, if I don't try I will never know.

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