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[Towertalk] Copper vs Zinc

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Subject: [Towertalk] Copper vs Zinc
From: (Ford Peterson)
Date: Tue, 30 Jul 2002 13:12:23 -0500
I'm building a bulkhead at the tower to terminate all feedlines at the tower
ground 35' from my shack wall.  Having listened to all the chatter about
"copper plates" being superior conductors and dissimilar metal issues, I'm
planning to use galv angle iron bolted between two of the legs of the Rohn
25G tower.  I'll terminate the feedlines (about 6 of them) to the angle iron
bracket.  Total cost -- in round numbers -- zippo.

The ARRL handbook describes the dielectric properties of various
mediums--most notably dry air-- at 21 volts per 0.001".  Realizing that
copper does conduct better, is there a point of diminishing returns when it
comes to fabricating hardware for lightning protection?  Finding copper
plates, etc. at the local hardware store is impossible.

Even if the connection between the tower, the angle iron, the connectors,
etc. become rusty, the gap is going to be very small.  Wet iron oxide is
hardly as good a dielectric as air and am presenting the 21v/.001" for
illustration since the handbook doesn't bother to describe the dielectric
properties of iron or zinc oxides.

I plan to use threaded barrel (SO239 types) on the each of the feedlines and
bond them to the angle bracket attached to the base of my tower.

Flame away guys.  I fail to be convinced that I need to spend $1000(s) of
on copper widgets, flangets, and a huge box full of fancy MOVs--only to take
a direct hit and fry anyway.


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