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
>_______________________________________________
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>See http://www.mscomputer.com
>
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>
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