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Securing COAX cable?

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  • Larry Phegley
    I think I had a problem with the connection between my antenna and the radio on my last balloon attempt and I have totally redone that layout. Now I have a
    Message 1 of 6 , Mar 19, 2013
      I think I had a problem with the connection between my antenna and the radio on my last balloon attempt and I have totally redone that layout.  Now I have a problem with the antenna lead.  I need to secure it so the torque from the antenna twisting in the wind does not tranfer to the SMA connection at the radio.  I have an electrician friend who said they use something called a kellum grip but he didn't think they made one for COAX.  Right now the suggestion is to embed the coax in silicon.  Do you have any other ideas?
       
      Larry
      KJ6PBS
       
    • Mike Manes
      Hi Larry, SMA s are pretty puny connectors for balloon payload antennas. I d use nothing less than a safety-wired BNC outside the enclosure. But if that s not
      Message 2 of 6 , Mar 19, 2013
        Hi Larry,

        SMA's are pretty puny connectors for balloon payload antennas. I'd
        use nothing less than a safety-wired BNC outside the enclosure. But
        if that's not an option, suggest forming a loop in the coax, preferably
        inside the payload and securing the loop with a tyrap. The loop should
        be sized such that it can't turn inside the payload when the coax is
        twisted from the outside.

        All of EOSS's payload antennas are connected to panel BNC-F connectors
        mounted rigidly to the enclosure. Inside, the BNC's transition to
        RG-174 for connection to the radios. The external coax is RG-142 -
        double-shielded teflon with a Kapton sheath; that stuff is
        indestructible! The shields are soldered to the BNC-M ferrules,
        and the BNC-M shells are fitted with lateral wire loops soldered
        in place to accept a safety wire (plastic-coated bread tie) strapped to
        a fixed point on the enclosure to prevent coax twisting from turning
        the bayonet.

        This practice was developed over the first 20 or so EOSS flights, where
        we got fed up with finding and fixing antennas that were damaged by PBC
        or rough landings.

        73 de Mike W5VSI


        On 3/19/13 4:38 PM, Larry Phegley wrote:
        >
        >
        > I think I had a problem with the connection between my antenna and the
        > radio on my last balloon attempt and I have totally redone that layout.
        > Now I have a problem with the antenna lead. I need to secure it so the
        > torque from the antenna twisting in the wind does not tranfer to the SMA
        > connection at the radio. I have an electrician friend who said they use
        > something called a kellum grip but he didn't think they made one for
        > COAX. Right now the suggestion is to embed the coax in silicon. Do you
        > have any other ideas?
        > Larry
        > KJ6PBS
        >
        >
        >
      • Floyd Rodgers
        Kellum grips are designed to support a vertical length of something round like wire. They are available in various diameter ranges, but I m not so sure they
        Message 3 of 6 , Mar 19, 2013
          Kellum grips are designed to support a vertical length of something
          round like wire. They are available in various diameter ranges, but I'm
          not so sure they are really for limiting axial rotation of the wire. You
          might consider an "SO" cord grip to do the same job. That is, a rubber
          bushing compression type connector usually with 1/2" conduit nipple and
          nut on the other end. Look in the Appleton catalog to see this stuff.
        • James Ewen
          ... Don t let the antenna twist in the wind. Don t create a situation where the antenna connector is bearing a load. We build a center-fed dipole using printed
          Message 4 of 6 , Mar 19, 2013
            On Tue, Mar 19, 2013 at 4:38 PM, Larry Phegley <larry.phegley@...> wrote:

            > I think I had a problem with the connection between my antenna and the
            > radio on my last balloon attempt and I have totally redone that layout. Now
            > I have a problem with the antenna lead. I need to secure it so the torque
            > from the antenna twisting in the wind does not tranfer to the SMA connection
            > at the radio. Do you have any other ideas?

            Don't let the antenna twist in the wind. Don't create a situation
            where the antenna connector is bearing a load.

            We build a center-fed dipole using printed circuit board to support
            the wire. We left that hanging below the payload but had a problem
            where the braid fractured due to flexing during PBC which can be seen
            here:

            http://bear.sbszoo.com/bear6/0236.jpg

            We got the last position report from this flight at 25,440 feet, yet
            still easily recovered by using a grid search downwind of the last
            reported location.

            We increased the size of the PCB material, and secured the feedline to
            the board, then embed the board into the side of the payload
            container. The feedline sees no stress, and the connector simply has
            to keep the feedline attached to the radio.


            --
            James
            VE6SRV
          • L. Paul Verhage
            Ditto here. My flight computer kits use PCBs to attach the antenna to the outside of the module. Paul
            Message 5 of 6 , Mar 19, 2013

              Ditto here. My flight computer kits use PCBs to attach the antenna to the outside of the module.

              Paul

              On Mar 19, 2013 8:54 PM, "James Ewen" <ve6srv@...> wrote:
              On Tue, Mar 19, 2013 at 4:38 PM, Larry Phegley <larry.phegley@...> wrote:

              > I think I had a problem with the connection between my antenna and the
              > radio on my last balloon attempt and I have totally redone that layout.  Now
              > I have a problem with the antenna lead.  I need to secure it so the torque
              > from the antenna twisting in the wind does not tranfer to the SMA connection
              > at the radio.   Do you have any other ideas?

              Don't let the antenna twist in the wind. Don't create a situation
              where the antenna connector is bearing a load.

              We build a center-fed dipole using printed circuit board to support
              the wire. We left that hanging below the payload but had a problem
              where the braid fractured due to flexing during PBC which can be seen
              here:

              http://bear.sbszoo.com/bear6/0236.jpg

              We got the last position report from this flight at 25,440 feet, yet
              still easily recovered by using a grid search downwind of the last
              reported location.

              We increased the size of the PCB material, and secured the feedline to
              the board, then embed the board into the side of the payload
              container. The feedline sees no stress, and the connector simply has
              to keep the feedline attached to the radio.


              --
              James
              VE6SRV


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            • Michael Willett
              A similar event happened with my payloads, I used a twin lead j-pole on the early flights. However, in PBC the lead was visible in the videos being thrashed
              Message 6 of 6 , Mar 20, 2013
                A similar event happened with my payloads, I used a twin lead j-pole on the early flights. However, in PBC the lead was visible in the videos being thrashed around with the 100 mph free fall that would fatigue the antenna itself. I had the RG-59 coax equipped with strain relief and it survived. I have now switched to all being flexible HT antennas with less drag and with great success. 

                --Michael



                On Mar 19, 2013, at 5:38 PM, Larry Phegley <larry.phegley@...> wrote:

                 

                I think I had a problem with the connection between my antenna and the radio on my last balloon attempt and I have totally redone that layout.  Now I have a problem with the antenna lead.  I need to secure it so the torque from the antenna twisting in the wind does not tranfer to the SMA connection at the radio.  I have an electrician friend who said they use something called a kellum grip but he didn't think they made one for COAX.  Right now the suggestion is to embed the coax in silicon.  Do you have any other ideas?
                 
                Larry
                KJ6PBS
                 

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