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7530Re: Feeding A Magnetic TX Loop

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  • Irv F
    Jun 2, 2010
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      --- In loopantennas@yahoogroups.com, toddroberts2001@... wrote:
      >
      > Hi All,
      > I am wondering if anyone has tried locating the feed loop
      > or Gamma match next to the tuning capacitor and if
      > they had success with this arrangement?
      >
      > This would simplify tuning/matching the loop and
      > simplify construction a bit if the tuning cap and
      > feedpoint could be located close together, especially for a
      > larger size loop. This is compared to the normal method
      > of locating the tuning capacitor at the opposite end of the loop
      > away from the feedpoint. This requires locating the tuning capacitor at
      > the highest point of the loop and complicates the mechanical
      > construction especially for a larger circumference loop like a 70
      > ft circumference loop for 80 meters.
      >
      > I know it will unbalance the loop if the gamma
      > match ground point is next to the tuning capacitor
      > but I don't see any reason why it wouldn't work.
      >
      > Unbalancing the loop should mainly effect the
      > sharpness of the null direction but for transmitting
      > most people want the antenna to be more omnidirectional.
      >
      > I plan to experiment with this feed method over the next
      > few months and will report on how it works for me. My test
      > loop will be a square loop 30-40ft circumference for 40
      > meters only for highest efficiency.
      >
      > 73 Todd WD4NGG
      >

      The portion of the loop opposite the capacitor is the only real
      place to get a low impedance feed point which the gamma match
      requires. You would have difficulty feeding the loop anywhere
      around the capacitor because of the very high voltages there.

      Believe me, it would greatly simplify the construction of the
      magloops if the feedpoint and capacitor could be colocated -- thats
      why you never see it in magloop articles.

      I'm in the process of building a loop now. Due to medical reasons
      I had to sell my house and move into a residence where I could get
      nursing assistance. I have a nice patio, and that's where the loop
      is going to sit. I just picked up a Yaesu ND-817 and am looking
      to get back on the air again. I'll propably build two loops in order to cover 80 thru 10M with a reasonably degree of efficiency.

      Irv VE6BP
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