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Re: [GPSL] Antennas for APRS

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  • HarryM
    I use 1/4 wave dipoles for both 2m and 70cm made from 2 pieces of flexible wire. I cover the “hot” lead with flexible plastic radio control antenna tubing,
    Message 1 of 14 , Jul 6, 2011
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      I use 1/4 wave dipoles for both 2m and 70cm made from 2 pieces of flexible wire. I cover the “hot” lead with flexible plastic radio control antenna tubing, leave the “gnd” lead just a loose piece of wire and attach both to the side of the capsules. They work very well! Just remember to check the SWR after attaching to the capsule because it will be different than not being on the capsule. As Mark stated the short antennas are very inefficient and I have seen those hard antennas poke through capsules during post-burst chaos and get ripped off on an OSU flight.
       
      73 Harry KC5TRB
      ORB
    • 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 2 of 14 , Jul 6, 2011
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        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 3 of 14 , Jul 6, 2011
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          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 4 of 14 , Jul 6, 2011
          • 0 Attachment
            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 5 of 14 , Jul 6, 2011
            • 0 Attachment
              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 6 of 14 , Jul 6, 2011
              • 0 Attachment
                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 7 of 14 , Jul 6, 2011
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                  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 8 of 14 , Jul 6, 2011
                  • 0 Attachment
                    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 9 of 14 , Jul 6, 2011
                    • 0 Attachment
                      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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