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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 6 , 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

       

    • Roelof Bakker
      Hello Chavdar, Thank you for the information, which is nice to know. On a more practical note, I have used your design to refurbish a defunct Wellbrook ALA1530
      Message 2 of 6 , Sep 10, 2013
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        Hello Chavdar,

        Thank you for the information, which is nice to know.

        On a more practical note, I have used your design to refurbish a defunct
        Wellbrook ALA1530 active loop.
        This is a loop with a diameter of 1 meter made of 22 mm aluminium tube.

        The input filter has not been installed.
        I found that the gain of the amplifier is too high for this application.
        The output amplifier uses emitter degeneration feedback to control the
        gain.
        The stage gain is the collector load divided my the un-bypassed part of
        the emitter resistor.
        I changed R5 and R13 to 56 ohm and R6 and R15 to 68 ohm and this gives
        excellent results.

        Thank you for publishing an excellent design.

        73,
        Roelof Bakker, pa0rdt
      • Alberto I2PHD
        ... Hello Roelof, could you please give a pointer to that loop amplifier design ? Thanks. -- /*73 Alberto I2PHD*/
        Message 3 of 6 , Sep 10, 2013
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          On 9/10/2013 11:41 AM, Roelof Bakker wrote:

          Thank you for publishing an excellent design.


          Hello Roelof,

            could you please give a pointer to that loop amplifier design ?  Thanks.

          --
          73 Alberto I2PHD
        • Roelof Bakker
          Hello Alberto, It can be found here: http://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm 73, Roelof, pa0rdt
          Message 4 of 6 , Sep 10, 2013
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            Hello Alberto,

            It can be found here:

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

            73,
            Roelof, pa0rdt
          • lz1aq
            Hello Roelof, Your modification is ok since you do not change the DC operatiing point. The gain in original design is needed mainly on higher bands above 10
            Message 5 of 6 , Sep 12, 2013
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               Hello Roelof,

              Your modification is ok since you do not change the DC operatiing point. The gain in original design is needed mainly on higher bands above 10 MHz where the signal levels are lower. This mignt be not true now when the sun activity is high but  I suppose we both hope to reach the next sun mimimum ...  - then I suppose you should have to return back the old resistor values :) I do not think that you have  any IMD problems unles a powerfull AM transimmiter is in the next street to your home.

              Have a fun

              Chavdar



              --- In perseus_sdr@yahoogroups.com, <roelof@...> wrote:

              Hello Alberto,

              It can be found here:

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

              73,
              Roelof, pa0rdt
            • Alberto I2PHD
              ... Thanks Roelof. I will build and test one to be used with my 1.5 meters loop in the garden... -- /*73 Alberto I2PHD*/
              Message 6 of 6 , Sep 12, 2013
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                On 9/10/2013 3:46 PM, Roelof Bakker wrote:

                Hello Alberto,
                
                It can be found here:
                
                http://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm
                
                73,
                Roelof, pa0rdt

                Thanks Roelof.  I will build and test one to be used with my 1.5 meters loop in the garden...


                --
                73 Alberto I2PHD
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