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7185Re: shielded loop

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  • Dave
    Feb 3, 2010
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      --- In loopantennas@yahoogroups.com, "dannibou" <dannibou@...> wrote:
      > Hi! On the topic of shielded loop, can anyone tell me if the metal for build a
      > loop is important electrically speaking. I've read on this group that aluminum
      > or copper are preferred. Is this because they are non magnetic metal? I have
      > a round piece of metal that I could use to build a shielded loop but it is
      > magnetized metal. Any idea? Thanks

      In general, ferromagnetic materials are a VERY poor choice for antennas.
      The problem is that, at RF frequencies, the currents flow on the very
      outer edge of the conductor (e.g., skin effect). For ferromagnetic materials,
      the ferromagnetic properties reduce the skin depth even more, and this
      tends to make ferromagnetic materials even more lossy than you'd
      normally expect.

      There are, of course, ways around this. The common approach is to
      plate the ferromagnetic material (and, we're usually talking about steel or
      some other Iron compound here) with a higher conductivity,
      non-ferromagnetic material. The prototypical plating material is Silver,
      due to it's high conductivity, but it's also possible to plate Copper onto
      steel (and, this is commercially available as CopperWeld (TM) antenna
      wire). Some television lead-in wire, and some telephone wire was also
      Copper plated steel.

      Failing that, the best wire is Silver, although price usually prevents
      the use of that except in very special circumstances (e.g.,
      military/government applications, very small microwave antennas, etc.).
      Following that, Copper wire is the next best material, quickly followed by
      Aluminum wire.

      > Danny

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