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Experimental Comparison of Small Wideband Magnetic Loops

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  • lz1aq
    Hello, I have made some more precise experiments to compare different wideband small magnetic loops working in short circuit mode ( the active amplifier is
    Message 1 of 3 , Sep 10, 2013
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      Hello,

       

      I have made some more precise experiments to compare different wideband small magnetic loops working in short circuit mode ( the active amplifier is with very low input impedance) :   "Experimental Comparison of Small Wideband Magnetic Loops"

      http://www.lz1aq.signacor.com/docs/experimental-comparison-v10.pdf

       

      This article is based on previous one:  "Wideband Active Small Magnetic Loop Antenna"

      http://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm

       

      There is also a spreadsheet  to calculate loop parameters: http://www.lz1aq.signacor.com/docs/w-loop-calc-v10.xls

       

      Chavdar LZ1AQ

      lz1aq@...

      www.lz1aq.signacor.com

    • vbifyz
      Hi Chavdar, Thank you for sharing these very interesting results. There is one more characteristic that is very important for loop antennas: null depth. It is
      Message 2 of 3 , Sep 10, 2013
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        Hi Chavdar,

        Thank you for sharing these very interesting results.
        There is one more characteristic that is very important for loop antennas: null depth. It is especially interesting for those of us who are not in a quiet rural location.
        Did you try to measure it?
        I guess it is defined more by the amplifier common mode rejection ratio, but should be some function of the loop geometry as well.

        73, Mike VE3YXA
      • lz1aq
        Hello Mike, A good loop balance (high common mode rejection) is essential in order to reach high null depth. Most often if the loop has different null depths
        Message 3 of 3 , Sep 11, 2013
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           Hello Mike,

          1. A good loop balance (high common mode rejection) is essential in order to reach high null depth. Most often if the loop has different null depths between its two sides the main reason is the poor common mode rejection
          2.  I have not measured carefully the loop null depth because it is very unstable below 20 dB level.  I think that one of the reasons is the polarization of the incoming wave. Model simulations show the small loop above real ground has significant horizontal polarization component rotated at 90 deg. to the vertical component.  The small loop has very deep null for vertically polarized waves but if the polarization of the wave is tilted slightly there will be the effect of reducing the null since in this direction the horizontal component of the loop pattern has its maximum.  So to null completely the source you should have to tilt slightly the loop.
          3. Model simulations show that in free space crossed coplanar loops have very weak horizontal component – almost null.  But above real ground the horizontal component is almost the same as in the ordinary single loop.
          4. My experiments show that 20 dB rejections is the normal limit for loop rejection. If you reach 20 dB rejection from both sides of the loop that means your loop is working properly.  By careful adjustment the man can gain some more dB but that is all. You  might reach a rejection above 30 dB  but the  null will be unstable  and will change with the weather conditions, loop tilt due to wind etc.

           73 Chavdar LZ1AQ

          lz1aq  at  abv.bg 

          www.lz1aq.signacor.com



          --- In loopantennas@yahoogroups.com, <loopantennas@yahoogroups.com> wrote:

          Hi Chavdar,

          Thank you for sharing these very interesting results.
          There is one more characteristic that is very important for loop antennas: null depth. It is especially interesting for those of us who are not in a quiet rural location.
          Did you try to measure it?
          I guess it is defined more by the amplifier common mode rejection ratio, but should be some function of the loop geometry as well.

          73, Mike VE3YXA
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