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10356RE: [loopantennas] Butterfly Capacitors from copper stock?

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  • redsp
    Dec 28, 2013
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      ---In loopantennas@{{emailDomain}}, <brian@...> wrote:

      ~Anyone looked at making butterfly capacitor kits from copper. The weld that MFJ used to attach their butterfly capacitor to their aluminum loop is a great concept but we all know that copper is better conductor, and if we could braze/solder the connection of the butterfly loop directly to the copper loop (Homebrew) this would be a lot more efficient.

       

      Copper is quite soft, easily bent, and difficult to de-burr. I would use thin brass for capacitor plates for its easier working and polishing//de-burring properties. It solders very easily, and I suspect that its conductivity is so close to copper that “there’s not enough difference to make a difference”.

       

      Cheers,

       

      Brian Burns  Ex: W5BRO, K6UCD

       

       

      See my website:  www.lessonsinlutherie.com





      Considering that the starting point was Aluminum and the change to copper was to improve the conductivity, then yes, Brass has a lower conductivity and *will* make a difference.  The resistivity of these materials in nOhm m are


      Cu - 17.1 

      Al - 26.5

      Brass - 64


      Of course the composition of Brass varies a bit and so will the resistivity, but it won't change enough to alter these relative amounts. 


      In changing from Aluminum to Copper, I would question the resistance of the soldered connection compared to the solid body of the Copper.   It may well be that the added resistance of the welded Aluminum is less than that of the soldered joints.  Solder is *much* better than mechanical connections, but I expect a weld is significantly better yet.  However the devil is in the details... just how good a solder joint you get. 


      Anyone have an idea of the relative resistance of the antenna materials to the radiation resistance?  Wouldn't  that be what determines when you have reached a point of diminishing returns in optimizing the material resistance?


      Rick

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