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[TowerTalk] Terminate braid at top of tower...or not?

To: towertalk@contesting.com
Subject: [TowerTalk] Terminate braid at top of tower...or not?
From: N3AE <n3ae@comcast.net>
Date: Sat, 1 Nov 2014 16:44:46 +0000 (UTC)
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
I've always wondered about terminating coax shields on the top of a crank-up 
tower. On one hand, I think that by doing that, you're encouraging lightning 
currents to go down the coax shield as the resistance between the tower 
sections of a crank-up is likely to be larger than the coax shield (assuming 
the shield is also bonded at the bottom of the tower). But perhaps the 
inductance of the coax is larger than that of the tower so most of the 
lightning current would still traverse the tower? On the other hand, by bonding 
the coax at the bottom and not at the top, you may have flash-over issues at 
the top because of the difference in potential of the tower and the coax shield 
at the top. Maybe I'm making this more complex than it is, but my gut tells me 
it is a bit more complex than it may first seem. 

All the commercial towers bond coax shields at the top, bottom and every 70-100 
ft or so, but they are not crank-ups with unknown continuity between the 
sections. 

N3AE 
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