>
>>>Make sure that you do not allow the cable to touch the tower. Normaly this
>>>would not be a problem except that the bare sheild will rub the tower and
>>>create noise. I know that the cable give-away is nice, but nothing is
>>>really free.
>>
>>Au contraire, make sure it is well and thoroughly grounded to the tower,
>>preferably running down the inside, for lightning reasons if nothing else.
>
>I thought aluminum on galvanized steel is a no-no due to dissimilar
>metals? (I'm glad the 3000' of hardline I just got is insulated!!!)
>---
>Chad Kurszewski, WE9V e-mail: WE9V@qth.com
>The Official "Sultans of Shwing" Web Site: http://www.QTH.com/sos
Take a look at how CATV bare hardline is used in its primary
application--CATV installations. It is usually run with a galvanized
"strand" cable and lashed directly to it with another strand of wire. If
contact between the aluminum cable jacket and the zinc coating on the
galvanized strand was a serious problem, I would think it would show up in
the thousands of miles of installed CATV cable and they would not install it
that way.
Also, if you actually study the "dissimilar metals" corrosion problem, you
will see that some combinations of dissimilar metals are much worse than
others. Aluminum and zinc are right next to each other on the chart of
"galvanic action" and therefore work quite well together with minumum
corrosion. Bare steel (stainless steel, for example) and aluminum are not
close to each other and it is not a particularily good combination for
galvanic action. My experience has been that the aluminum next to stainless
steel tends to turn to white powder over time and the stainless steel
remains bright and free of corrosion. I use galvanized steel hardware on my
beams, when I can get it, for the larger bolts used for splicing boom
sections or mounting booms to masts.
Consulting the chart of galvanic action of metals (a good college chemistry
book will have this chart) will also show you that zinc and iron (the main
element in steel) are also not very close to each other. I think this is
why once the zinc coating has been broken, rusting of the steel underneath
occurs very rapidly since the two dissimilar metals (zinc and iron) are now
exposed to the weather. I have several examples of turnbuckles and wire
rope clips that are rusted over their entire surface and others, installed
at the same time, that are not rusted at all. But then, I'm not a
metalurgist, either, so maybe I'm wrong again . . .
Is there a good metalurgist out there who can comment on this?
Stan w7ni@teleport.com
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