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

[Don]

That is a great question. I also have a tall crankup and am in a very 
corrosive salt air environment where is difficult (not impossible but one 
has to be methodical) to seal off connectors using all the best practice 
methods. I'm now using the flooded heat shrink and 3M liquid seal on the 
shrink ends over connection joints and connectors where I can. Liberal use 
of CorrosionBlock on the connector threads and tips too. How would one 
terminate/bond the coax shields at the tower top in a manner that would not 
leave something open to potential corrosion?

Don W7WLL

-----Original Message----- 
From: N3AE
Sent: Saturday, November 01, 2014 9:44 AM
To: towertalk at contesting.com
Subject: [TowerTalk] Terminate braid at top of tower...or not?

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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