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Re: [loopantennas] Re: Transmitting Loop Antenna

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  • Chris Trask
    Tony, That chart is total resistance (radiation plus loss). In a 2-part series I wrote for QEX back in 2003, I had a similar chart for a 1m diameter loop made
    Message 1 of 21 , Oct 1, 2008
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      Tony,
      That chart is total resistance (radiation plus loss). In a 2-part series I wrote for QEX back in 2003, I had a similar chart for a 1m diameter loop made with 0.25" tubing. There, you can see that the resistance is going from a first-order (linear) to second-order (nonlinear) curve as it approaches the first parallel resonance. The analytical approaches used in that article show this as well.

      I'm going to make a bending form so that I can make loops from 1/2" rigid copper pipe and see if there's a difference in the resistance. I'm curious as to whether the other metals in the flexible tubing alloy (zinc?) are significantly raising the loss resistance. I couldn't find anything online about this.

      Nor could I find anything about a homebrewed pipe bender. It was suggested some time ago to use a large spring that plumbers use in bending PVC pipe, but those are not long enough for bending a 10-foot piece of copper pipe into a 1m radius arc. Guess I'll make a heavy form out of plywood and fill the pipe with sand.


      >
      >> I finally completed the testing and construction of a new form of
      >> transmitting loop antenna. .....
      >
      >Looks great, Chris. I studied the paper, and have one question.
      >
      >Figure 1. shows the radiation resistance vs. frequency of a 1.5 M
      >loop, which are the measured, not calculated, values.
      >
      >My question is, how is the radiation resistance so high? The highest I
      >have ever seen as a predicted value is much lower than that, even for
      >methods that claim traditional values are too small.
      >
      >To what do you attribute this high radiation resistance? I would like
      >to build one of these, but would like to believe it works as it is
      >supposed to.
      >
      >Thanks.
      >
      >Tony WA3HRL
      >


      Chris

      ,----------------------. High Performance Mixers and
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      / extinct stuff, anyhow? /
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      _ |/ Principal Engineer
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      (__)\ _ P.O. Box 25240
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      \ \ / \
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    • dldorrance
      Hi Chris, Like Tony, I would like to see some way of estimating total total resistance, in order to know what size loop for what band(s) will transform with
      Message 2 of 21 , Oct 1, 2008
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        Hi Chris,

        Like Tony, I would like to see some way of estimating total total
        resistance, in order to know what size loop for what band(s) will
        transform with what total step up value of transmission line
        transformer(s).

        Regarding bending copper pipe. Are you talking about standard copper
        pipe, or are you talking about soft copper tubing, which comes in 1/2
        diameters in most hardware stores and should be easy to fashion into a
        circle?

        Dave WA6YSO
      • dldorrance
        last sentence should be 1/2 inch *diameter* copper tubing... Dave WA6YSO
        Message 3 of 21 , Oct 1, 2008
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          last sentence should be 1/2 inch *diameter* copper tubing...

          Dave WA6YSO

          --- In loopantennas@yahoogroups.com, "dldorrance" <dldorrance@...> wrote:
          >
          > Hi Chris,
          >
          > Like Tony, I would like to see some way of estimating total total
          > resistance, in order to know what size loop for what band(s) will
          > transform with what total step up value of transmission line
          > transformer(s).
          >
          > Regarding bending copper pipe. Are you talking about standard copper
          > pipe, or are you talking about soft copper tubing, which comes in 1/2
          > diameters in most hardware stores and should be easy to fashion into a
          > circle?
          >
          > Dave WA6YSO
          >
        • Chris Trask
          ... I ve already published measured resistances for 1/4 and 1/2 copper tubing for a couple of different diameter loops. You can estimate the resistance for
          Message 4 of 21 , Oct 1, 2008
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            >
            > Like Tony, I would like to see some way of estimating total total
            > resistance, in order to know what size loop for what band(s) will
            > transform with what total step up value of transmission line
            > transformer(s).
            >

            I've already published measured resistances for 1/4" and 1/2" copper
            tubing for a couple of different diameter loops. You can estimate the
            resistance for other sizes and bands by scaling them.

            >
            > Regarding bending copper pipe. Are you talking about standard copper
            > pipe, or are you talking about soft copper tubing, which comes in 1/2
            > diameters in most hardware stores and should be easy to fashion into a
            > circle?
            >

            That would be 1/2" rigid copper pipe for later on. I'm already using
            the flexible tubing in 1/4" and 1/2" diameters.




            Chris

            ,----------------------. High Performance Mixers and
            / What's all this \ Amplifiers for RF Communications
            / extinct stuff, anyhow? /
            \ _______,--------------' Chris Trask / N7ZWY
            _ |/ Principal Engineer
            oo\ Sonoran Radio Research
            (__)\ _ P.O. Box 25240
            \ \ .' `. Tempe, Arizona 85285-5240
            \ \ / \
            \ '" \ IEEE Senior Member #40274515
            . ( ) \
            '-| )__| :. \ Email: christrask@...
            | | | | \ '. http://www.home.earthlink.net/~christrask
            c__; c__; '-..'>.__

            Graphics by Loek Frederiks
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