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[Towertalk] tower joint Conductivity ???

To: <towertalk@contesting.com>
Subject: [Towertalk] tower joint Conductivity ???
From: RedHaines@centurytel.net (Red)
Date: Tue, 19 Nov 2002 10:45:12 -0600
I certainly agree with Steve.  It is difficult to assure conductivity of 
the tower unless it is bypassed with joint-free conductors, or welded 
together.

Assuring high conductivity of the tower joints is more important for 
lightning protection than for HF performance.  Capacitance across the 
joints will probably be sufficient to conduct HF, especially in the 
higher frequency bands, but the low frequency components of lightning 
will develop high potential across those joints unless conductivity is 
high.  Running a one-piece conductor down each tower leg  reduces that 
uncertainty.  The physical contacts in most towers are probably 
adequate, but are not assured and degradation over time is possible. 
 Joint compound is a good idea to assure conductivity, and may make 
assembly and disassembly easier.

Joints in the Universal aluminum towers are upside down; the upper 
section fits into the lower section.  This makes it easier for water to 
migrate through the joint to affect the joint compound and promote 
corrosion.  I'm considering sealing each joint on the outside, top, with 
good quality caulking, and may also run an aluminum conductor down each 
leg of my Universal.  I also bypass the tower leg  to base joints with 
ground conductors that are welded to the re-bar cage and continue, 
unbroken, to a system of distributed ground rods, all for lightning bypass.

Overkill?  Probably.  However, the alternatives are to engineer more and 
trust to luck.  I've engineered it to the limit of my knowledge and 
equipment and I believe more in Murphy's laws than I trust to luck. 
 I've spent thousands on my hobby, and choose not to jeopardize the 
investment for a few hundred dollars spent for lightning protection.

73 de WO0W

K7LXC@aol.com wrote:

>In a message dated 11/19/02 1:03:16 AM Pacific Standard Time, 
>xppq@pyramid.net writes:
>
>  
>
>>Given a Tower of Rohn 45 - to be shunt
>> fed on Low bands -  Is it NECESSARY
>> to run WIRES top to bottom OR is the
>> conductivity at the tower joints good enough
>> to perform well as VERTICAL radiator ??
>> 
>> Should I use conductive grease?
>>    
>>
>
>    I would. But hard to predict the conductivity of the whole tower. 
>
>Cheers,
>Steve    K7LXC
>TOWER TECH 
>_______________________________________________
>AN Wireless Self Supporting Towers at discounted prices, 
>See http://www.mscomputer.com 
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