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7183shielded loop

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  • Missouri Guy
    Feb 2, 2010
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      >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
      Danny
      >

      Danny,

      Copper or AL is used because it has less RF resistance than
      iron. Also, those two metals won't have a tendancy to rust
      away outdoors.

      The metal "shield" is actually part of the antenna. You can
      prove that to yourself by touching the metal loop and noticing
      that the loop detunes when you touch it. So, really, if your
      loop is mounted "in the clear", it doesn't make a bit of
      difference in sensistivity or directivity whether it's shielded
      or not (read more below). If the loop is very near some
      metal objects, there might be some benefit of having the shield.

      A loop that is UN-shielded may have a higher 'Q' because of
      less distributed capacitance....depends on how it is wound.
      Having a higher 'Q' usually results in a more sensitive
      loop, but with narrower (sharper) tuning. The crystal
      radio boys know this and some have constructed
      large loops of large litz wire (the right type of litz) for
      that very purpose.

      Charlie, N0TT

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