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3815Re: Tranmitting Loop for 6m & 10m

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  • Len Warner
    Aug 1, 2007
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      At 9:05 pm ((PDT)) Tue Jul 31, 2007, in Digest 882, de_9w2dtr wrote:

      >--- In loopantennas@yahoogroups.com, W2XJ <w2xj@...> wrote:
      > >
      > >
      > > I agree that the loop is too large. The circumference needs to be less
      > > than 1/4 wave. With 47 cm diameter, you are right at 1/4 wave length
      > > before you consider velocity and loading. If you go to a diameter
      > > slightly less than 40 CM, it should tune on 6 M and be about 60 %
      > > efficient on 10 M if you use around 1 inch (25mm) tubing. Also, your
      > > capacitor is to large. You need about 26 pf for 10 m and half that
      >on 6.
      > > With a capacitor 10 times too large, tuning at the bottom of the
      >range
      > > could be difficult. What kind of match are you using - gamma match or
      > > loop coupling? How much power do you plan to use?
      > >
      >
      >I am using a Farady Loop

      Faraday: Michael Faraday, an English natural philosopher
      http://en.wikipedia.org/wiki/Michael_Faraday

      >for coupling the RF feed.
      >Is there any usage of Balun and tuner should be considered?

      A balun provides a BAlanced to UNbalanced (or an
      unbalanced to balanced) transformation.

      You only need one if your antenna coupling is balanced
      and your feedre is unbalanced; or your antenna coupling
      is unbalanced and your feeder is balanced.

      > From my calculation, with the velocity factor of 0.66,

      Where did you get that from? The velocity factor is one
      in free space - are you operating in some sticky liquid?

      >or 54Mhz
      >frequency. The loop diameter for 1/4w will be about 29cm. Is this
      >correct? I use this formula, 300/54=5.55, 5.55/4=1.388,
      >1.388*0.66=0.916, 0.916/pi=29.1cm.
      >
      >I am using a 12mm microwave coax cable for the loop.

      If you are calculating the loop dimensions using the
      velocity factor of your coax, remember that the loop is
      radiating from the outside of the conductor and this
      has nothing to do with what is happening inside the
      coax (otherwise, how would coax feeders work?)


      Regards, LenW
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