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Re: [TowerTalk] Mounting Polyphaser IS-RCT to SPGP

To: jimlux <>
Subject: Re: [TowerTalk] Mounting Polyphaser IS-RCT to SPGP
From: John Kemker <>
Date: Fri, 12 Jun 2009 12:26:30 -0400
List-post: <">>
Aluminum has 60% of the conductivity of copper.  That's not "almost the 
same."  In order to get the equivalent conductivity out of aluminum, you 
have to make it thicker, which isn't always the best choice, based upon 
the skin effect of lightning conduction.  For good mechanical 
properties, screw your copper to MDF and utilize that material's 
mechanical properties.  That's what PolyPhaser does.  That's what is 
recommended by I.C.E. as well.  Engineers who design lightning 
protection systems for large installations generally recommend copper 
ground plates, not aluminum, for that very reason.

Of course, not every engineer designing lightning protection systems is 
going to specify copper for ground plates.  Also, there's lots of people 
out there using aluminum who have not had problems with lightning.  This 
is just my opinion, based upon the information available to me.  Make 
your own decision.

jimlux wrote:
> Dick Green wrote:
>> Why do you advise against an aluminum ground plate? Are you only against 
>> outdoor use or indoor as well? I have a pair of Hoffmann metal utility 
>> cabinets with aluminum grounding plates inside. They seem to be fine and 
>> haven't corroded a bit.
>> 73, Dick WC1M
>>> -----Original Message-----
>>> From: John Kemker []
>>> Sent: Thursday, June 11, 2009 11:47 PM
>>> To: Peter Dougherty
>>> Cc:
>>> Subject: Re: [TowerTalk] Mounting Polyphaser IS-RCT to SPGP
>>> The ICE might be a better solution, in any case.  However, to each their
>>> own.
>>> I'd advise against the aluminum and seriously check out
>>> for their copper plates.  VERY reasonable prices
>>> for 12"x12" sheets and straps.  I just got two in the mail that I'll be
> I was wondering the same.  Aluminum is almost the same conductivity as 
> copper and much cheaper and easier to machine.  For the same money, one 
> can probably get thicker aluminum (better mechanical properties..)
> One advantage of copper is that you can solder to it (although soldering 
> to a big sheet is challenging from a heat standpoint), but bolted 
> connections to aluminum work pretty well, especially if you use one of 
> the goops designed for the purpose.

73 de W5NNH
10X 75371/M&M 117/SMIRK 6185/Six Club 285/TRA 2499/Norcross 228 F&AM

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