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14846Re: AW: AW: [SDRSharp] ebay antenna

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  • jdow
    Jun 24, 2014
      I remembered from WAY back that tarnish was a fairly good conductor. It
      appears that may be a VERY old urban legend. (I learned it in the late
      50s or so. It has serious legs! I think it always referred to the relay
      case specifically. Contact pressure and wiping can make huge differences.
      For non-wiping contacts tiny relays don't use silver these days, I believe.
      Gold works nicely. It's malleability guarantees good contact area.)

      {O.O} Joanne

      On 2014/06/24 18:02, Ken Alexander k.alexander@... [SDRSharp] wrote:
      > I stand corrected! Either the information I received was incorrect or I mis-remembered it! That's a word...isn't it? :-)
      >
      > 73 - Ken
      >
      >
      >
      >> On Jun 24, 2014, at 8:27 PM, "jdow jdow@... [SDRSharp]" <SDRSharp@...> wrote:
      >>
      >> This prompted me to do a little research.
      >>
      >> Silver oxide is non-conductive except in certain forms such as used in silver
      >> zinc batteries. It doesn't form easily.
      >>
      >> Silver sulfide is the usual surface film of tarnish seen most often. It, too,
      >> is a non-conductor in bulk. In practical terms on relay contacts it increases
      >> the contact resistance by a factor of about 3. So it's not bad but it's not
      >> good either.
      >>
      >> Copper oxide and copper sulfide are less well behaved.
      >>
      >> In antennas you can actually end up with better performance over time with
      >> anodized aluminum. It's surface doesn't conduct. So you have a very thin
      >> layer of dielectric over the conducting aluminum. Add a nice layer of Krylon
      >> sprayed over it all and the antenna will last a long time with little
      >> change in performance over the years. You simply use a larger conductor to
      >> make up for the poorer conductivity. (Krylon over silver or copper is not as
      >> nicely behaved. I believe it may have sulfur in it. Many people use these
      >> combinations anyway. So it may not be as bad as I suspect.)
      >>
      >> In constructing the antenna keep screws and bolts out of the electrical path
      >> as much as possible. They are not as well behaved, either.
      >>
      >> And, yes, I mucked up in my memory about gold's conductivity. I for some
      >> idiot reason thought it was further down than third place in the usual
      >> scale (pre graphene).
      >>
      >> {^_^}
      >>
      >>> On 2014/06/24 14:38, Ken Alexander k.alexander@... [SDRSharp] wrote:
      >>>
      >>>
      >>> Seems to me I read somewhere that one of the advantages of silver is that not
      >>> only is it a good conductor, but the oxide (tarnish) coating that forms is an
      >>> equally good conductor. I'm going from memory, so feel free to shoot down this
      >>> assertion if you know better. *:) happy
      >>>
      >>> Gold of course doesn't oxidize. Another great reason it makes a good contact
      >>> material.
      >
      >
      > ------------------------------------
      > Posted by: Ken Alexander <k.alexander@...>
      > ------------------------------------
      >
      >
      > ------------------------------------
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