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Re: [GPSL] Antennas for APRS

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  • Mike Manes
    Hi Larry(?), You didn t mention what frequency your APRS beacon is intended to operate on, but unless you can provide your own I-gate and digis, I m guessing
    Message 1 of 14 , Jul 6, 2011
      Hi Larry(?),

      You didn't mention what frequency your APRS beacon is intended to operate on,
      but unless you can provide your own I-gate and digis, I'm guessing that you
      plan to put it on the 2m APRS backbone of 144.390 MHz. In that case, such
      a small antenna will be extremely inefficient, both due to its having a
      near-zero radiation resistance (50 ohms is optimal) and its having such a
      small E-M aperture.

      Although some folks have got by with embedding their beacon antennas inside
      their payload, my experience is that radiated transmit signal will couple
      strongly into nearby susceptible electronic circuitry causing some serious
      functional upsets. This can occur even if the antenna radiating element is
      outside the payload enclosure when there is no counterpoise for an end fed
      element, i.e., no ground plane.

      EOSS has had great luck using wire J-pole antennas with 2 - 3 ft of rugged
      50 ohm coax (RG-142) feedline. The MFJ pocket rollup 2m J-pole with the
      RG-58 replaced with -142 can work, but we roll our own using heavy-duty
      300 twin lead for the 1/4 wave matching section and teflon insulated #24
      AWG for the 1/2 wave radiator. The coax is fitted with a BNC male, and the
      payload with a rear-mount threaded BNC male with RG-175 going from it to
      the radio inside the payload.

      Be sure to strap the J-pole to the woven nylon payload support line at
      3 or spots, leaving plenty of slack in the wire to accommodate stretch
      in the nylon line.

      73 de Mike W5VSI
      CTO EOSS

      73 de Mike W5VSI



      On 7/5/2011 10:20, phegleyl wrote:
      > I am getting ready to purchase some electronics for my first balloon satellite. I need to buy an antenna for my APRS tracker. I was going through a catalog over the weekend and noticed a very small antenna maybe just over an inch long. It would be convenient to have the antenna internal to the payload but would such an antenna be efficient?
      >
      >
      >
      > ------------------------------------
      >
      > Yahoo! Groups Links
      >
      >
      >
      >

      --
      Mike Manes mrmanes@... Tel: 303-979-4899
      "Things should be made as simple as possible, but not more so."
      A. Einstein
    • Phegley, Mr. Larry
      Thanks for your help. Yes, I am targeting 144.39MHz. I had to go look up what a J-Pole is. So does this just hang from the payload with something to
      Message 2 of 14 , Jul 6, 2011
        Thanks for your help. Yes, I am targeting 144.39MHz. I had to go look up what a J-Pole is. So does this just hang from the payload with something to separate the J from the Pole? If so, what would be the difference between a J-Pole and just a long wire? Can a long wire function at 1/2 wavelength? No one seems to be using a long wire!


        Larry Phegley
        Meteorologist
        com'l 831 656 4752
        DSN 878 4752
        -----Original Message-----
        From: Mike Manes [mailto:mrmanes@...]
        Sent: Wednesday, July 06, 2011 1:39 PM
        To: GPSL@yahoogroups.com
        Cc: Phegley, Mr. Larry
        Subject: Re: [GPSL] Antennas for APRS

        Hi Larry(?),

        You didn't mention what frequency your APRS beacon is intended to operate on, but unless you can provide your own I-gate and digis, I'm guessing that you plan to put it on the 2m APRS backbone of 144.390 MHz. In that case, such a small antenna will be extremely inefficient, both due to its having a near-zero radiation resistance (50 ohms is optimal) and its having such a small E-M aperture.

        Although some folks have got by with embedding their beacon antennas inside their payload, my experience is that radiated transmit signal will couple strongly into nearby susceptible electronic circuitry causing some serious functional upsets. This can occur even if the antenna radiating element is outside the payload enclosure when there is no counterpoise for an end fed element, i.e., no ground plane.

        EOSS has had great luck using wire J-pole antennas with 2 - 3 ft of rugged 50 ohm coax (RG-142) feedline. The MFJ pocket rollup 2m J-pole with the
        RG-58 replaced with -142 can work, but we roll our own using heavy-duty 300 twin lead for the 1/4 wave matching section and teflon insulated #24 AWG for the 1/2 wave radiator. The coax is fitted with a BNC male, and the payload with a rear-mount threaded BNC male with RG-175 going from it to the radio inside the payload.

        Be sure to strap the J-pole to the woven nylon payload support line at
        3 or spots, leaving plenty of slack in the wire to accommodate stretch in the nylon line.

        73 de Mike W5VSI
        CTO EOSS

        73 de Mike W5VSI



        On 7/5/2011 10:20, phegleyl wrote:
        > I am getting ready to purchase some electronics for my first balloon satellite. I need to buy an antenna for my APRS tracker. I was going through a catalog over the weekend and noticed a very small antenna maybe just over an inch long. It would be convenient to have the antenna internal to the payload but would such an antenna be efficient?
        >
        >
        >
        > ------------------------------------
        >
        > Yahoo! Groups Links
        >
        >
        >
        >

        --
        Mike Manes mrmanes@... Tel: 303-979-4899
        "Things should be made as simple as possible, but not more so."
        A. Einstein
      • Pete Lilja
        We use a Roll-up slim Jim (eBay item # 320655602511 ) on our flights. I m pretty sure I can t build one for this price. He ll tune it to 144.39 on request.
        Message 3 of 14 , Jul 6, 2011
          We use a Roll-up slim Jim (eBay item # 320655602511 ) on our flights.  I'm pretty sure I can't build one for this price.  He'll tune it to 144.39 on request.
          These work amazingly well.  They are robust and take the flight 'issues' like a champ.  They will 'spin' on the way up it seems so you need to take care to solidly contain the PL259 connector that comes with it so your connection the the radio itself doesn't break.
           
          ( I have no connection to this eBay seller other than a satified customer.)
           
          Pete
          KC0GPB
          On Wed, Jul 6, 2011 at 4:26 PM, Phegley, Mr. Larry <larry.phegley@...> wrote:
           

          Thanks for your help. Yes, I am targeting 144.39MHz. I had to go look up what a J-Pole is. So does this just hang from the payload with something to separate the J from the Pole? If so, what would be the difference between a J-Pole and just a long wire? Can a long wire function at 1/2 wavelength? No one seems to be using a long wire!

          Larry Phegley
          Meteorologist
          com'l 831 656 4752
          DSN 878 4752


          -----Original Message-----
          From: Mike Manes [mailto:mrmanes@...]
          Sent: Wednesday, July 06, 2011 1:39 PM
          To: GPSL@yahoogroups.com
          Cc: Phegley, Mr. Larry
          Subject: Re: [GPSL] Antennas for APRS

          Hi Larry(?),

          You didn't mention what frequency your APRS beacon is intended to operate on, but unless you can provide your own I-gate and digis, I'm guessing that you plan to put it on the 2m APRS backbone of 144.390 MHz. In that case, such a small antenna will be extremely inefficient, both due to its having a near-zero radiation resistance (50 ohms is optimal) and its having such a small E-M aperture.

          Although some folks have got by with embedding their beacon antennas inside their payload, my experience is that radiated transmit signal will couple strongly into nearby susceptible electronic circuitry causing some serious functional upsets. This can occur even if the antenna radiating element is outside the payload enclosure when there is no counterpoise for an end fed element, i.e., no ground plane.

          EOSS has had great luck using wire J-pole antennas with 2 - 3 ft of rugged 50 ohm coax (RG-142) feedline. The MFJ pocket rollup 2m J-pole with the
          RG-58 replaced with -142 can work, but we roll our own using heavy-duty 300 twin lead for the 1/4 wave matching section and teflon insulated #24 AWG for the 1/2 wave radiator. The coax is fitted with a BNC male, and the payload with a rear-mount threaded BNC male with RG-175 going from it to the radio inside the payload.

          Be sure to strap the J-pole to the woven nylon payload support line at
          3 or spots, leaving plenty of slack in the wire to accommodate stretch in the nylon line.

          73 de Mike W5VSI
          CTO EOSS

          73 de Mike W5VSI

          On 7/5/2011 10:20, phegleyl wrote:
          > I am getting ready to purchase some electronics for my first balloon satellite. I need to buy an antenna for my APRS tracker. I was going through a catalog over the weekend and noticed a very small antenna maybe just over an inch long. It would be convenient to have the antenna internal to the payload but would such an antenna be efficient?
          >
          >
          >
          > ------------------------------------
          >
          > Yahoo! Groups Links
          >
          >
          >
          >

          --
          Mike Manes mrmanes@... Tel: 303-979-4899
          "Things should be made as simple as possible, but not more so."
          A. Einstein


        • Mike Manes
          Hi Larry, OK - so I guess you ve abandoned the 1-inch dummy load then? Here s the scoop on the J-pole. The radiating element is the 1/2 wave wire, and as you
          Message 4 of 14 , Jul 6, 2011
            Hi Larry,

            OK - so I guess you've abandoned the 1-inch dummy load then?

            Here's the scoop on the J-pole. The radiating element is the 1/2 wave
            wire, and as you may recall from your ham radio studies, a 1/2 wave end
            fed wire has a very high feedpoint impedance, like several K-ohms, which
            would make for a poor match to, and power transfer from, a 50-ohm source,
            such as darn near any VHF ham rig. The J part serves as a transmission
            line impedance transformer. It's got a short at the end farthest from
            the pole end, and since it's 1/4 wave long, it looks like a real high
            impedance at the pole end, where the 1/2 wave radiating element is connected.
            So the apparent impedance measured at various points along that 1/4 wave line
            varies from zero at the shorted end to near-infinite at the opposite end.
            Somewhere between the two ends, one can find what appears to be 50 ohms,
            and that's where one connects the 50-ohm coax going back to the radio.
            For a 2m J-pole, that point is about 1-1/4" up from the shorted end.

            The J-pole can sort of be considered a "long wire", since if one built one
            for 80m, the 1/2 wave pole would be like 125 ft long!. A 1/2 wave vertical
            radiator has a nice single-lobed radiation pattern that peaks at the horizon.
            One could extend the pole on out to a full wave, but then you'd get a two-
            lobe pattern with a null at the horizon - so you'd have a tough time hearing
            it at any distance during final descent, which is when you'd most like to
            hear it.

            So there's no spacing between the J and Pole parts.

            Other folks, including EOSS, have used simpler commercial antennas such as
            rubber ducks for HTs, but then you face the issue of possible problems
            with counterpoise currents getting into the naughty bits inside the payload,
            or building a counterpoise (ground plane) right at the duck's feed point.
            An effective ground plane should be integral odd multiples of 1/4 wave (19" at
            144 MHz), so it can get beat up pretty badly during PBC or landing. The J-pole
            is quite robust during those assaults, however.

            73 de Mike W5VSI

            On 7/6/2011 15:26, Phegley, Mr. Larry wrote:
            > Thanks for your help. Yes, I am targeting 144.39MHz. I had to go look
            up what a J-Pole is. So does this just hang from the payload with something
            to separate the J from the Pole? If so, what would be the difference between
            a J-Pole and just a long wire? Can a long wire function at 1/2 wavelength?
            No one seems to be using a long wire!
            >
            >
            > Larry Phegley
            > Meteorologist
            > com'l 831 656 4752
            > DSN 878 4752
            > -----Original Message-----
            > From: Mike Manes [mailto:mrmanes@...]
            > Sent: Wednesday, July 06, 2011 1:39 PM
            > To: GPSL@yahoogroups.com
            > Cc: Phegley, Mr. Larry
            > Subject: Re: [GPSL] Antennas for APRS
            >
            > Hi Larry(?),
            >
            > You didn't mention what frequency your APRS beacon is intended to operate on, but unless you can provide your own I-gate and digis, I'm guessing that you plan to put it on the 2m APRS backbone of 144.390 MHz. In that case, such a small antenna will be extremely inefficient, both due to its having a near-zero radiation resistance (50 ohms is optimal) and its having such a small E-M aperture.
            >
            > Although some folks have got by with embedding their beacon antennas inside their payload, my experience is that radiated transmit signal will couple strongly into nearby susceptible electronic circuitry causing some serious functional upsets. This can occur even if the antenna radiating element is outside the payload enclosure when there is no counterpoise for an end fed element, i.e., no ground plane.
            >
            > EOSS has had great luck using wire J-pole antennas with 2 - 3 ft of rugged 50 ohm coax (RG-142) feedline. The MFJ pocket rollup 2m J-pole with the
            > RG-58 replaced with -142 can work, but we roll our own using heavy-duty 300 twin lead for the 1/4 wave matching section and teflon insulated #24 AWG for the 1/2 wave radiator. The coax is fitted with a BNC male, and the payload with a rear-mount threaded BNC male with RG-175 going from it to the radio inside the payload.
            >
            > Be sure to strap the J-pole to the woven nylon payload support line at
            > 3 or spots, leaving plenty of slack in the wire to accommodate stretch in the nylon line.
            >
            > 73 de Mike W5VSI
            > CTO EOSS
            >
            > 73 de Mike W5VSI
            >
            >
            >
            > On 7/5/2011 10:20, phegleyl wrote:
            >> I am getting ready to purchase some electronics for my first balloon satellite. I need to buy an antenna for my APRS tracker. I was going through a catalog over the weekend and noticed a very small antenna maybe just over an inch long. It would be convenient to have the antenna internal to the payload but would such an antenna be efficient?
            >>
            >>
            >>
            >> ------------------------------------
            >>
            >> Yahoo! Groups Links
            >>
            >>
            >>
            >>
            >

            --
            Mike Manes mrmanes@... Tel: 303-979-4899
            "Things should be made as simple as possible, but not more so."
            A. Einstein
          • Mike Manes
            PVC sheathed coax, like RG-58, shatters like glass at stratospheric temps. That s why we use RG-142: teflon dielectric, silver plated and double shielded with
            Message 5 of 14 , Jul 6, 2011
              PVC sheathed coax, like RG-58, shatters like glass at stratospheric temps.
              That's why we use RG-142: teflon dielectric, silver plated and double
              shielded with a Kapton sheath. It's pricey at about a buck a foot, but
              ours have made it through well over 50 flights each so far with no damage.
              So it's cheap compared to losing a whole payload string due to loss of
              a beacon signal.

              On 7/6/2011 07:58, Mark Conner wrote:
              >
              >
              > A short antenna will not be all that efficient in getting your signal out, and
              > probably will introduce a lot of RF into the payload. I have had good luck
              > with using whip antennas (around 7-12" long) and a bulkhead connector (SMA or
              > BNC, depending on your radio and preferences) through a thin aluminum plate
              > which helps serve as a ground plane. The plate is about 4" square, not really
              > enough for a 2m signal but better than nothing.
              >
              > The antenna should be oriented vertically for best results. I have mine on
              > top of the payload so it's not damaged as much on landing.
              >
              > I used to use a ladder-line J-pole antenna hanging about 3 feet below the
              > payload. This worked very well, but the plastic on the coax sheath and the
              > ladder line became brittle in the cold. Plus during a power-line landing in
              > 2001 I managed to short two phases of a 30-kV 3-phase line.
              >
              > 73 de Mark N9XTN
              >
              > On Tue, Jul 5, 2011 at 11:20, phegleyl <larry.phegley@...
              > <mailto:larry.phegley@...>> wrote:
              >
              > I am getting ready to purchase some electronics for my first balloon
              > satellite. I need to buy an antenna for my APRS tracker. I was going
              > through a catalog over the weekend and noticed a very small antenna maybe
              > just over an inch long. It would be convenient to have the antenna
              > internal to the payload but would such an antenna be efficient?
              >
              >
              >
              > ------------------------------------
              >
              > Yahoo! Groups Links
              >
              >
              >
              >
              >
              >
              >

              --
              Mike Manes mrmanes@... Tel: 303-979-4899
              "Things should be made as simple as possible, but not more so."
              A. Einstein
            • Mike Manes
              Any vertical radiator will have a null off the end. And if you re right under the payload using another vertical on your car, then both nulls align, so the
              Message 6 of 14 , Jul 6, 2011
                Any vertical radiator will have a null off the end. And if you're right
                under the payload using another vertical on your car, then both nulls
                align, so the sig goes way down. One fix is to move your mag mount from
                the top of the car off to the side, so your mobile's pattern is aimed
                upwards - that won't eliminate the null from the payload antenna, but
                usually gets enough signal back to copy OK. And during descent, the
                payload antenna is going to swing about, as does its null.

                On 7/6/2011 08:28, Roger Hammond wrote:
                >
                >
                > My last flight I used the old traditional half-wave dipole. It performed quite
                > well, but had a huge null below it. Which may have been because of the
                > orientation.
                >
                > Rog KC0MWM
                >
                > On Wed, Jul 6, 2011 at 8:58 AM, Mark Conner <mconner1@...
                > <mailto:mconner1@...>> wrote:
                >
                >
                >
                > A short antenna will not be all that efficient in getting your signal out,
                > and probably will introduce a lot of RF into the payload. I have had good
                > luck with using whip antennas (around 7-12" long) and a bulkhead connector
                > (SMA or BNC, depending on your radio and preferences) through a thin
                > aluminum plate which helps serve as a ground plane. The plate is about 4"
                > square, not really enough for a 2m signal but better than nothing.
                >
                > The antenna should be oriented vertically for best results. I have mine
                > on top of the payload so it's not damaged as much on landing.
                >
                > I used to use a ladder-line J-pole antenna hanging about 3 feet below the
                > payload. This worked very well, but the plastic on the coax sheath and
                > the ladder line became brittle in the cold. Plus during a power-line
                > landing in 2001 I managed to short two phases of a 30-kV 3-phase line.
                >
                > 73 de Mark N9XTN
                >
                >
                > On Tue, Jul 5, 2011 at 11:20, phegleyl <larry.phegley@...
                > <mailto:larry.phegley@...>> wrote:
                >
                > I am getting ready to purchase some electronics for my first balloon
                > satellite. I need to buy an antenna for my APRS tracker. I was going
                > through a catalog over the weekend and noticed a very small antenna
                > maybe just over an inch long. It would be convenient to have the
                > antenna internal to the payload but would such an antenna be efficient?
                >
                >
                >
                > ------------------------------------
                >
                > Yahoo! Groups Links
                >
                >
                > <mailto:GPSL-fullfeatured@yahoogroups.com>
                >
                >
                >
                >
                >
                >
                >
                >

                --
                Mike Manes mrmanes@... Tel: 303-979-4899
                "Things should be made as simple as possible, but not more so."
                A. Einstein
              • L. Paul Verhage
                I use a dipole with elements attached to a PCB. I ll bring one to GPSL so you can see it. Paul ... -- Onwards and Upwards, Paul
                Message 7 of 14 , Jul 6, 2011
                  I use a dipole with elements attached to a PCB. I'll bring one to GPSL so you can see it.
                   
                  Paul

                  On Wed, Jul 6, 2011 at 5:08 PM, Mike Manes <mrmanes@...> wrote:
                  Hi Larry,

                  OK - so I guess you've abandoned the 1-inch dummy load then?

                  Here's the scoop on the J-pole.  The radiating element is the 1/2 wave
                  wire, and as you may recall from your ham radio studies, a 1/2 wave end
                  fed wire has a very high feedpoint impedance, like several K-ohms, which
                  would make for a poor match to, and power transfer from, a 50-ohm source,
                  such as darn near any VHF ham rig.  The J part serves as a transmission
                  line impedance transformer.  It's got a short at the end farthest from
                  the pole end, and since it's 1/4 wave long, it looks like a real high
                  impedance at the pole end, where the 1/2 wave radiating element is connected.
                  So the apparent impedance measured at various points along that 1/4 wave line
                  varies from zero at the shorted end to near-infinite at the opposite end.
                  Somewhere between the two ends, one can find what appears to be 50 ohms,
                  and that's where one connects the 50-ohm coax going back to the radio.
                  For a 2m J-pole, that point is about 1-1/4" up from the shorted end.

                  The J-pole can sort of be considered a "long wire", since if one built one
                  for 80m, the 1/2 wave pole would be like 125 ft long!.  A 1/2 wave vertical
                  radiator has a nice single-lobed radiation pattern that peaks at the horizon.
                  One could extend the pole on out to a full wave, but then you'd get a two-
                  lobe pattern with a null at the horizon - so you'd have a tough time hearing
                  it at any distance during final descent, which is when you'd most like to
                  hear it.

                  So there's no spacing between the J and Pole parts.

                  Other folks, including EOSS, have used simpler commercial antennas such as
                  rubber ducks for HTs, but then you face the issue of possible problems
                  with counterpoise currents getting into the naughty bits inside the payload,
                  or building a counterpoise (ground plane) right at the duck's feed point.
                  An effective ground plane should be integral odd multiples of 1/4 wave (19" at
                  144 MHz), so it can get beat up pretty badly during PBC or landing. The J-pole
                  is quite robust during those assaults, however.

                  73 de Mike W5VSI

                  On 7/6/2011 15:26, Phegley, Mr. Larry wrote:
                  >   Thanks for your help.  Yes, I am targeting 144.39MHz.  I had to go look
                  up what a J-Pole is.  So does this just hang from the payload with something
                  to separate the J from the Pole?  If so, what would be the difference between
                  a J-Pole and just a long wire?  Can a long wire function at 1/2 wavelength?
                  No one seems to be using a long wire!
                  >
                  >
                  > Larry Phegley
                  > Meteorologist
                  > com'l 831 656 4752
                  > DSN 878 4752
                  > -----Original Message-----
                  > From: Mike Manes [mailto:mrmanes@...]
                  > Sent: Wednesday, July 06, 2011 1:39 PM
                  > To: GPSL@yahoogroups.com
                  > Cc: Phegley, Mr. Larry
                  > Subject: Re: [GPSL] Antennas for APRS
                  >
                  > Hi Larry(?),
                  >
                  > You didn't mention what frequency your APRS beacon is intended to operate on, but unless you can provide your own I-gate and digis, I'm guessing that you plan to put it on the 2m APRS backbone of 144.390 MHz.  In that case, such a small antenna will be extremely inefficient, both due to its having a near-zero radiation resistance (50 ohms is optimal) and its having such a small E-M aperture.
                  >
                  > Although some folks have got by with embedding their beacon antennas inside their payload, my experience is that radiated transmit signal will couple strongly into nearby susceptible electronic circuitry causing some serious functional upsets.  This can occur even if the antenna radiating element is outside the payload enclosure when there is no counterpoise for an end fed element, i.e., no ground plane.
                  >
                  > EOSS has had great luck using wire J-pole antennas with 2 - 3 ft of rugged 50 ohm coax (RG-142) feedline.  The MFJ pocket rollup 2m J-pole with the
                  > RG-58 replaced with -142 can work, but we roll our own using heavy-duty 300 twin lead for the 1/4 wave matching section and teflon insulated #24 AWG for the 1/2 wave radiator.  The coax is fitted with a BNC male, and the payload with a rear-mount threaded BNC male with RG-175 going from it to the radio inside the payload.
                  >
                  > Be sure to strap the J-pole to the woven nylon payload support line at
                  > 3 or spots, leaving plenty of slack in the wire to accommodate stretch in the nylon line.
                  >
                  > 73 de Mike W5VSI
                  > CTO EOSS
                  >
                  > 73 de Mike W5VSI
                  >
                  >
                  >
                  > On 7/5/2011 10:20, phegleyl wrote:
                  >> I am getting ready to purchase some electronics for my first balloon satellite.  I need to buy an antenna for my APRS tracker.  I was going through a catalog over the weekend and noticed a very small antenna maybe just over an inch long.  It would be convenient to have the antenna internal to the payload but would such an antenna be efficient?
                  >>
                  >>
                  >>
                  >> ------------------------------------
                  >>
                  >> Yahoo! Groups Links
                  >>
                  >>
                  >>
                  >>
                  >

                  --
                  Mike Manes    mrmanes@...     Tel: 303-979-4899
                  "Things should be made as simple as possible, but not more so."
                  A. Einstein


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                  --
                  Onwards and Upwards,
                  Paul
                • Mike Manes
                  There s about $2 worth of ladder line and $2 of coax and connector in there. The RG-58 PVC sheath is subject to cracking in the -50C cold; replace it with
                  Message 8 of 14 , Jul 6, 2011
                    There's about $2 worth of ladder line and $2 of coax and connector in there.
                    The RG-58 PVC sheath is subject to cracking in the -50C cold; replace it
                    with RG-142 and it will last forever (in balloonatic years). You could
                    save a lot of weight by replacing the 1/2 wave section of ladder line with
                    a single #26 teflon wire - which would also narrow the VSWR bandwidth, but
                    just start long and trim it for min VSWR at 144.39 MHz. Replace the PL-259
                    with a BNC and save even more weight; adding a wire tab to the BNC-M shell
                    provides a spot to tie a safety wire to prevent the BNC bayonet from
                    unlocking in flight.

                    73 de Mike W5VSI

                    On 7/6/2011 15:36, Pete Lilja wrote:
                    >
                    >
                    > We use a Roll-up slim Jim (eBay item # 320655602511 ) on our flights. I'm
                    > pretty sure I can't build one for this price. He'll tune it to 144.39 on request.
                    > These work amazingly well. They are robust and take the flight 'issues' like
                    > a champ. They will 'spin' on the way up it seems so you need to take care to
                    > solidly contain the PL259 connector that comes with it so your connection the
                    > the radio itself doesn't break.
                    > ( I have no connection to this eBay seller other than a satified customer.)
                    > Pete
                    > KC0GPB
                    > On Wed, Jul 6, 2011 at 4:26 PM, Phegley, Mr. Larry
                    > <larry.phegley@... <mailto:larry.phegley@...>> wrote:
                    >
                    > __
                    >
                    > Thanks for your help. Yes, I am targeting 144.39MHz. I had to go look up
                    > what a J-Pole is. So does this just hang from the payload with something
                    > to separate the J from the Pole? If so, what would be the difference
                    > between a J-Pole and just a long wire? Can a long wire function at 1/2
                    > wavelength? No one seems to be using a long wire!
                    >
                    > Larry Phegley
                    > Meteorologist
                    > com'l 831 656 4752
                    > DSN 878 4752
                    >
                    >
                    > -----Original Message-----
                    > From: Mike Manes [mailto:mrmanes@... <mailto:mrmanes%40gmail.com>]
                    > Sent: Wednesday, July 06, 2011 1:39 PM
                    > To: GPSL@yahoogroups.com <mailto:GPSL%40yahoogroups.com>
                    > Cc: Phegley, Mr. Larry
                    > Subject: Re: [GPSL] Antennas for APRS
                    >
                    > Hi Larry(?),
                    >
                    > You didn't mention what frequency your APRS beacon is intended to operate
                    > on, but unless you can provide your own I-gate and digis, I'm guessing
                    > that you plan to put it on the 2m APRS backbone of 144.390 MHz. In that
                    > case, such a small antenna will be extremely inefficient, both due to its
                    > having a near-zero radiation resistance (50 ohms is optimal) and its
                    > having such a small E-M aperture.
                    >
                    > Although some folks have got by with embedding their beacon antennas
                    > inside their payload, my experience is that radiated transmit signal will
                    > couple strongly into nearby susceptible electronic circuitry causing some
                    > serious functional upsets. This can occur even if the antenna radiating
                    > element is outside the payload enclosure when there is no counterpoise for
                    > an end fed element, i.e., no ground plane.
                    >
                    > EOSS has had great luck using wire J-pole antennas with 2 - 3 ft of rugged
                    > 50 ohm coax (RG-142) feedline. The MFJ pocket rollup 2m J-pole with the
                    > RG-58 replaced with -142 can work, but we roll our own using heavy-duty
                    > 300 twin lead for the 1/4 wave matching section and teflon insulated #24
                    > AWG for the 1/2 wave radiator. The coax is fitted with a BNC male, and the
                    > payload with a rear-mount threaded BNC male with RG-175 going from it to
                    > the radio inside the payload.
                    >
                    > Be sure to strap the J-pole to the woven nylon payload support line at
                    > 3 or spots, leaving plenty of slack in the wire to accommodate stretch in
                    > the nylon line.
                    >
                    > 73 de Mike W5VSI
                    > CTO EOSS
                    >
                    > 73 de Mike W5VSI
                    >
                    > On 7/5/2011 10:20, phegleyl wrote:
                    > > I am getting ready to purchase some electronics for my first balloon
                    > satellite. I need to buy an antenna for my APRS tracker. I was going
                    > through a catalog over the weekend and noticed a very small antenna maybe
                    > just over an inch long. It would be convenient to have the antenna
                    > internal to the payload but would such an antenna be efficient?
                    > >
                    > >
                    > >
                    > > ------------------------------------
                    > >
                    > > Yahoo! Groups Links
                    > >
                    > >
                    > >
                    > >
                    >
                    > --
                    > Mike Manes mrmanes@... <mailto:mrmanes%40gmail.com> Tel: 303-979-4899
                    > "Things should be made as simple as possible, but not more so."
                    > A. Einstein
                    >
                    >
                    >
                    >
                    >

                    --
                    Mike Manes mrmanes@... Tel: 303-979-4899
                    "Things should be made as simple as possible, but not more so."
                    A. Einstein
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