[TowerTalk] Aluminum longevity?

[K8RI on Tower talk]

I have some antennas that have been in use at least 30 years. This includes 
three different sites.  The only one that gave me a problem was a Cushcraft 
ATB-34 and that was at the feed point.

They use a phenolic center insulator for the driven element. A balun is 
atached to each side of the driven element with a 1/4-20 SS screw and lock 
nut. The connection is just the pressure from the end of the SS screw 
against the aluminum inside the phenolic.

Even though the screws were turned down very tight, over the years there was 
just enough corrosion between the disimilar metals to cause a high 
resistance.  Retightening the screws cured the problem, but I chose to pull 
the element halves out of the phenolic, polish the ends with Scotchbrite(TM) 
pads, reassemble, and then coat with about 3 or 4 coats of clear Krylon. 
That beam had been up at this site for over 15 years after that treatment 
with no problems, when I replaced it with a TH-5 a couple of years back.  Of 
course I would like to replace the TH-5 with something *bigger*. <:-))

73

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com

> All:
>
> Before I go to the trouble of coating the exterior of my new M2 Yagi, is
> aluminum corrosion a real problem with the alloys used today?
>
> Shouldn't the natural oxydation protect the surface of the antenna and 
> stop
> corrosion? What about the inside of the elements and boom? If surface
> corrosion is a real problem, what's the sense of protecting the outside if
> the inside is left bare?
>
> I have a F12 antenna that's been up for 6 years. The aluminum is certainly
> dull, but I don't see any corrosion. The clamps are rusted to hell, but 
> the
> rest is in fine shape.
>
> So, what's the average life expectancy of aluminum before corrosion takes
> it's toll and the antenna needs replacing?
>
> 73, Tony KT2Q
>
>
>
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