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RE: RE: [GRARA] J-Pole Build Results

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  • roberts358
    Bob, Thank you for your suggestion. I made a simple choke coil with five turns of the coax as suggested on one of the internet sites.. I will read about the
    Message 1 of 8 , Sep 3, 2013
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      Bob,

       

      Thank you for your suggestion. I made a simple choke coil with five turns of the coax as suggested on one of the internet sites.. I will read about the use of a balun.

       

      73s

       

      KD8VHV - Rob 



      --- In GRARA@yahoogroups.com, <grara@yahoogroups.com> wrote:

      A balun is essential with a J-Pole.  J-Poles are very sensitive to common mode currents.

       

      Can be a commercial one or a simple as many wraps of coax around a torrid as close to the antenna as possible.

       

      If different length coax changes things then you have a common mode current problem because the coax is part of the antenna.  See the antenna hand book.

       

      For what it is worth J

       

       

       

      From: GRARA@yahoogroups.com [mailto:GRARA@yahoogroups.com] On Behalf Of Hank Greeb
      Sent: Tuesday, September 03, 2013 12:00 PM
      To: GRARA@yahoogroups.com
      Subject: Re: [GRARA] J-Pole Build Results

       




      You didn't say where you were measuring the SWR, i.e. how long of coax you were using to connect to the antenna analyzers. With SWR on the Coax, the "apparent SWR" can change depending on the length of the feedline.  It also appears that the MFJ-259B doesn't provide Resistive, Inductive, or Capacitive reactance figures, so SWR, whilst useful, is not a definitive matter.

      Try adjusting the tap (point "C") up and/or down about 1/4" or so at a time and see if the SWR @ 146 MHz improves. 

      You "should" be able to find a point where the coax sees 50 ohms resistive.

      In my experience with VHF antenna, the general rule is that practical, empirical, trial and error, generally trumps theoretical.

      Besides, 1.6 SWR is not bad atall - most rigs tolerate SWR <= 2 with no difficulty.  So, I'm >99.44% sure you won't burn up the finals of your rig if you use it as is.

      72/73 de n8xx Hg
      QRP >99.44% of the time


      On 9/3/2013 10:58 AM, roberts358@... wrote:

      Well, as a new HAM I wanted to get some input on my latest build results of a ½” copper j-pole.

      I built to spec using the Ham Universe site calculator listed below. My results were not great and I thought that I would ask for some advice from the "Pro's".

      http://www.hamuniverse.com/jpole.html (Building)

      I built as close to the specs as I could and my results are listed below.

      http://www.hamuniverse.com/testingswr.html (Testing)

      Using an antenna analyzer (MFJ-259B - http://www.mfjenterprises.com/Product.php?productid=MFJ-259B). Thank you to Mark – K8GAP for his generous gift of allowing me the use of the analyzer in my build projects. I hope to purchase a device of my own soon. I tried hard to get better results using this analyzer, however, in the end my results ended as follows.

      144 MHz - 2.1 SWR
      146 MHz - 1.6 SWR
      148 MHz - 1.2 SWR


      It is very clear that the antenna resonates best at the higher end of the band. It would appear that the antenna is too short. I built the antenna to measurements calculated to 146 MHz.

      Before I give my ideas I thought that I would ask for the opinion of others in their build results

      Thanks Everyone,

      Rob - KD8VHV





    • Bob Hardin
      Rob, The choke coil is a good thing. If you put those 5 turns thru a toroid say type 31 it will be even better. Mike in Holland repair shop has them.
      Message 2 of 8 , Sep 4, 2013
      • 0 Attachment

        Rob,

         

        The choke coil is a good thing.

        If you put those 5 turns thru a toroid say type 31 it will be even better.  Mike in Holland repair shop has them.

        Choke/balun/unun whatever you want to call it, does the same thing. J

         

        Bob

         

        From: GRARA@yahoogroups.com [mailto:GRARA@yahoogroups.com] On Behalf Of roberts358@...
        Sent: Tuesday, September 03, 2013 9:12 PM
        To: GRARA@yahoogroups.com
        Subject: RE: RE: [GRARA] J-Pole Build Results

         




        Bob,

         

        Thank you for your suggestion. I made a simple choke coil with five turns of the coax as suggested on one of the internet sites.. I will read about the use of a balun.

         

        73s

         

        KD8VHV - Rob 



        --- In GRARA@yahoogroups.com, <grara@yahoogroups.com> wrote:

        A balun is essential with a J-Pole.  J-Poles are very sensitive to common mode currents.

         

        Can be a commercial one or a simple as many wraps of coax around a torrid as close to the antenna as possible.

         

        If different length coax changes things then you have a common mode current problem because the coax is part of the antenna.  See the antenna hand book.

         

        For what it is worth J

         

         

         

        From: GRARA@yahoogroups.com [mailto:GRARA@yahoogroups.com] On Behalf Of Hank Greeb
        Sent: Tuesday, September 03, 2013 12:00 PM
        To: GRARA@yahoogroups.com
        Subject: Re: [GRARA] J-Pole Build Results

         



        You didn't say where you were measuring the SWR, i.e. how long of coax you were using to connect to the antenna analyzers. With SWR on the Coax, the "apparent SWR" can change depending on the length of the feedline.  It also appears that the MFJ-259B doesn't provide Resistive, Inductive, or Capacitive reactance figures, so SWR, whilst useful, is not a definitive matter.

        Try adjusting the tap (point "C") up and/or down about 1/4" or so at a time and see if the SWR @ 146 MHz improves. 

        You "should" be able to find a point where the coax sees 50 ohms resistive.

        In my experience with VHF antenna, the general rule is that practical, empirical, trial and error, generally trumps theoretical.

        Besides, 1.6 SWR is not bad atall - most rigs tolerate SWR <= 2 with no difficulty.  So, I'm >99.44% sure you won't burn up the finals of your rig if you use it as is.

        72/73 de n8xx Hg
        QRP >99.44% of the time


        On 9/3/2013 10:58 AM, roberts358@... wrote:

        Well, as a new HAM I wanted to get some input on my latest build results of a ½” copper j-pole.

        I built to spec using the Ham Universe site calculator listed below. My results were not great and I thought that I would ask for some advice from the "Pro's".

        http://www.hamuniverse.com/jpole.html (Building)

        I built as close to the specs as I could and my results are listed below.

        http://www.hamuniverse.com/testingswr.html (Testing)

        Using an antenna analyzer (MFJ-259B - http://www.mfjenterprises.com/Product.php?productid=MFJ-259B). Thank you to Mark – K8GAP for his generous gift of allowing me the use of the analyzer in my build projects. I hope to purchase a device of my own soon. I tried hard to get better results using this analyzer, however, in the end my results ended as follows.

        144 MHz - 2.1 SWR
        146 MHz - 1.6 SWR
        148 MHz - 1.2 SWR


        It is very clear that the antenna resonates best at the higher end of the band. It would appear that the antenna is too short. I built the antenna to measurements calculated to 146 MHz.

        Before I give my ideas I thought that I would ask for the opinion of others in their build results

        Thanks Everyone,

        Rob - KD8VHV







      • roberts358
        Bob, Thank you for the suggestions and will look for contact information for the repair shop. 73s KD8VHV - Rob --- In GRARA@yahoogroups.com,
        Message 3 of 8 , Sep 4, 2013
        • 0 Attachment

          Bob,

           

          Thank you for the suggestions and will look for contact information for the repair shop.

           

          73s

           

          KD8VHV - Rob 



          --- In GRARA@yahoogroups.com, <grara@yahoogroups.com> wrote:

          Rob,

           

          The choke coil is a good thing.

          If you put those 5 turns thru a toroid say type 31 it will be even better.  Mike in Holland repair shop has them.

          Choke/balun/unun whatever you want to call it, does the same thing. J

           

          Bob

           

          From: GRARA@yahoogroups.com [mailto:GRARA@yahoogroups.com] On Behalf Of roberts358@...
          Sent: Tuesday, September 03, 2013 9:12 PM
          To: GRARA@yahoogroups.com
          Subject: RE: RE: [GRARA] J-Pole Build Results

           




          Bob,

           

          Thank you for your suggestion. I made a simple choke coil with five turns of the coax as suggested on one of the internet sites.. I will read about the use of a balun.

           

          73s

           

          KD8VHV - Rob 



          --- In GRARA@yahoogroups.com, <grara@yahoogroups.com> wrote:

          A balun is essential with a J-Pole.  J-Poles are very sensitive to common mode currents.

           

          Can be a commercial one or a simple as many wraps of coax around a torrid as close to the antenna as possible.

           

          If different length coax changes things then you have a common mode current problem because the coax is part of the antenna.  See the antenna hand book.

           

          For what it is worth J

           

           

           

          From: GRARA@yahoogroups.com [mailto:GRARA@yahoogroups.com] On Behalf Of Hank Greeb
          Sent: Tuesday, September 03, 2013 12:00 PM
          To: GRARA@yahoogroups.com
          Subject: Re: [GRARA] J-Pole Build Results

           



          You didn't say where you were measuring the SWR, i.e. how long of coax you were using to connect to the antenna analyzers. With SWR on the Coax, the "apparent SWR" can change depending on the length of the feedline.  It also appears that the MFJ-259B doesn't provide Resistive, Inductive, or Capacitive reactance figures, so SWR, whilst useful, is not a definitive matter.

          Try adjusting the tap (point "C") up and/or down about 1/4" or so at a time and see if the SWR @ 146 MHz improves. 

          You "should" be able to find a point where the coax sees 50 ohms resistive.

          In my experience with VHF antenna, the general rule is that practical, empirical, trial and error, generally trumps theoretical.

          Besides, 1.6 SWR is not bad atall - most rigs tolerate SWR <= 2 with no difficulty.  So, I'm >99.44% sure you won't burn up the finals of your rig if you use it as is.

          72/73 de n8xx Hg
          QRP >99.44% of the time


          On 9/3/2013 10:58 AM, roberts358@... wrote:

          Well, as a new HAM I wanted to get some input on my latest build results of a ½” copper j-pole.

          I built to spec using the Ham Universe site calculator listed below. My results were not great and I thought that I would ask for some advice from the "Pro's".

          http://www.hamuniverse.com/jpole.html (Building)

          I built as close to the specs as I could and my results are listed below.

          http://www.hamuniverse.com/testingswr.html (Testing)

          Using an antenna analyzer (MFJ-259B - http://www.mfjenterprises.com/Product.php?productid=MFJ-259B). Thank you to Mark – K8GAP for his generous gift of allowing me the use of the analyzer in my build projects. I hope to purchase a device of my own soon. I tried hard to get better results using this analyzer, however, in the end my results ended as follows.

          144 MHz - 2.1 SWR
          146 MHz - 1.6 SWR
          148 MHz - 1.2 SWR


          It is very clear that the antenna resonates best at the higher end of the band. It would appear that the antenna is too short. I built the antenna to measurements calculated to 146 MHz.

          Before I give my ideas I thought that I would ask for the opinion of others in their build results

          Thanks Everyone,

          Rob - KD8VHV







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