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  • jeremydayauburn
    Hi all. I am the communications lead on a student-run high altitude balloon project, and we are considering a new TNC. I was sent here by Gary Dion, N4TXI,
    Message 1 of 9 , Sep 6, 2007
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      Hi all. I am the communications lead on a student-run high altitude
      balloon project, and we are considering a new TNC. I was sent here by
      Gary Dion, N4TXI, and have been looking through the documentation and
      files on the Tracker 2.

      Myself and two other students have 1.5 weeks to come up with complete
      design documentation for our communications subsystem, so I don't have
      as much time as I would like to peruse the documents and messages at
      my leisure. So I would like to entreat any of you who could to help
      orient me as far as the specifications, features, problems, work
      involved, etc. that go along with attempting to use a Tracker2 in our
      balloon. The features that we need are:

      -Restricted Digipeat Capability
      -GPS Telemetry Data in NMEA format

      I'd like to see all SMT components if possible (weight
      considerations), but this isn't necessary.

      Any help I could get would be greatly appreciated.

      Thanks and 73 ~ Jeremy Day KI4PRZ
    • Jason Winningham
      ... what sort of restrictions? ... why NMEA format? That is the most inefficient position packet type in terms of bandwidth. Bandwidth also equates to power
      Message 2 of 9 , Sep 6, 2007
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        On Sep 6, 2007, at 1:26 PM, jeremydayauburn wrote:

        > -Restricted Digipeat Capability

        what sort of restrictions?

        > -GPS Telemetry Data in NMEA format

        why NMEA format? That is the most inefficient position packet type
        in terms of bandwidth. Bandwidth also equates to power consumption
        (transmitter is running longer).

        I don't know if the T2 will spit out NMEA by itself, but since it's a
        full TNC you could certainly use it (maybe with a microcontroller?)
        to get NMEA on the air.

        > I'd like to see all SMT components if possible (weight
        > considerations), but this isn't necessary.

        My understanding is that the production model T2 is SMT, but I have
        the PTH version and there won't be that much difference.

        -Jason
        kg4wsv
      • Scott Miller
        ... Digipeater capability is no problem. The T2 doesn t output GPS telemetry over the air in NMEA format - it s too inefficient and makes you choose between
        Message 3 of 9 , Sep 6, 2007
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          > -Restricted Digipeat Capability
          > -GPS Telemetry Data in NMEA format
          >
          > I'd like to see all SMT components if possible (weight
          > considerations), but this isn't necessary.

          Digipeater capability is no problem. The T2 doesn't output GPS
          telemetry over the air in NMEA format - it's too inefficient and makes
          you choose between course/speed and altitude in a given packet.

          It supports the standard APRS position format, plus Base91 compressed
          format. It'll still give you course/speed and altitude, plus HDOP and
          number of satellites in use if you need that.

          Also, if you're running in Garmin binary mode, you can get rate-of-climb
          in feet per minute. If someone can send me some sample data with the
          proprietary $PGRMV sentence with some vertical velocity (like from a
          plane) for testing I'll see if I can implement that for NMEA mode as
          well. It'll still only work on Garmins, though.

          The OT2m rev 1.0 (formerly Prototype E) is SMT with the exception of the
          connectors and such. The T2-135 is significantly lighter, but doesn't
          have power control for a cutdown device and would need a 5 volt power
          supply and close attention to radio interfacing since it's only intended
          to be used with the Alinco DR-135T.

          I do have some really small (unpopulated) Tracker2 boards on hand still,
          but they suffered from oscillator problems, and I'm not even sure if
          I've got all of the documentation and parts for those still.

          The T2-135 is available now, and the OT2m (the one in the metal case)
          should be here in another two weeks or so if all goes well. The factory
          just contacted me this morning for clarification on some parts, and
          somehow there was a shortage of voltage regulators, but nothing that
          should slow down production.

          Scott
        • James Ewen
          ... By complete communications subsystem, does that include things outside of the APRS tracker? ... The OT2 will do what you ask, but as others have indicated
          Message 4 of 9 , Sep 6, 2007
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            On 9/6/07, jeremydayauburn <dayjerd@...> wrote:

            > Myself and two other students have 1.5 weeks to come up with complete
            > design documentation for our communications subsystem

            By complete communications subsystem, does that include things outside
            of the APRS tracker?

            > The features that we need are:
            >
            > -Restricted Digipeat Capability
            > -GPS Telemetry Data in NMEA format
            >
            > I'd like to see all SMT components if possible (weight
            > considerations), but this isn't necessary.

            The OT2 will do what you ask, but as others have indicated NMEA is
            out. I am assuming that you simply want lat/long/cse/spd/alt data. The
            OT2 will do this.

            One thing that you want to be aware of is that you do NOT want to
            digipeat on 144.390 simplex. Listen on a seperate frequency, and
            downlink onto 144.390. Once your balloon gets a couple thousand feet
            in the air, it will never hear a quiet time on 144.390, and will
            appear to be locked up. Balloon borne trackers need to ignore the
            energy on the channel, and transmit blind. Digipeaters need to listen
            for uplink audio, and at altitude, it can be extremely noisy.

            We sent up a digital camera last month, and are still dealing with the
            aftermath. Our project got featured on digg.com and gizmodo.org. At
            least 6 major papers have featured the story, as well as CBC radio,
            Global Television, and CTV.

            Have a peek at the website for some background information. The BEAR
            site has detailed information about the payload construction, as well
            as telemetry data, etc. The SABLE site has photos and other
            information from that set of launches.

            We are planning on setting an altitude record in October with BEAR-III.

            http://bear.sbszoo.com

            Scott, any chances of an OT2 in a tiny SMT version for balloon flights
            like the OT+ SMT?

            It would be great to have digipeating capability as well as the
            ability to change flight parameters in flight by sending messages to
            the payload.

            We are stuffing the payload inside the balloon to reduce total mass,
            and the OT2 won't fit in the nozzle!

            James
            VE6SRV
          • Scott Miller
            ... I did run a digipeater on 144.39. I think I had QUIET set to 0, though, so it ll ignore the fact that the channel is busy. SWDCD should be ON. I was
            Message 5 of 9 , Sep 6, 2007
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              > One thing that you want to be aware of is that you do NOT want to
              > digipeat on 144.390 simplex. Listen on a seperate frequency, and
              > downlink onto 144.390. Once your balloon gets a couple thousand feet
              > in the air, it will never hear a quiet time on 144.390, and will
              > appear to be locked up. Balloon borne trackers need to ignore the

              I did run a digipeater on 144.39. I think I had QUIET set to 0, though,
              so it'll ignore the fact that the channel is busy. SWDCD should be ON.
              I was using a non-standard alias, of course - don't want to digipeat
              all of southern California and Nevada's WIDEn-N traffic!

              > Scott, any chances of an OT2 in a tiny SMT version for balloon flights
              > like the OT+ SMT?

              I was thinking of an OT1+ with integrated Copernicus GPS engine and 500
              mW transmitter. (Wasn't I talking to you about that the other day,
              James?) If and when I get a compact transceiver an all-in-one T2 would
              be a possibility. In fact, I'm doing that with the more expensive
              commercial 6-watt RF boards.

              The big problem with a tiny T2 board is that the demand's not really
              high enough to warrant automated production, and the part count is
              enough to make it a pain to produce in-house.

              Scott
            • Jeremy Day
              I guess I should clear up a few things: I meant that the GPS input would be NMEA protocol. Output from the TNC to the radio is (I assume) AX.25 standard. Also,
              Message 6 of 9 , Sep 6, 2007
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                I guess I should clear up a few things:

                I meant that the GPS input would be NMEA protocol. Output from
                the TNC to the radio is (I assume) AX.25 standard.

                Also, by restricted digipeat capability, I mean having the digipeater
                listen only for packets from our chase vehicles, which would (I hope)
                be the only packets on whatever frequency we chose. This frequency
                should be different from the national APRS frequency.

                Thanks to everyone for their input.

                Jeremy Day
                Communications Lead
                Auburn High Altitude Balloon Team
                space.auburn.edu
              • Scott Miller
                Ok. NMEA input is fine, of course. As I mentioned, Garmin binary mode will give you vertical speed, but you ll also get estimated position error rather than
                Message 7 of 9 , Sep 6, 2007
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                  Ok. NMEA input is fine, of course. As I mentioned, Garmin binary mode
                  will give you vertical speed, but you'll also get estimated position
                  error rather than HDOP, and time will be off a bit due to the lack of
                  leap second handling in the current firmware.

                  You can restrict digipeating by using a non-standard alias. I think I
                  used AIR for mine. You just need to set the path appropriately on the
                  stations using it.

                  And to clarify further on the NMEA thing, all APRS output is going to be
                  AX.25 (well, unless you're running PSK31 anyway) - but APRS lets you use
                  NMEA or one of three or four other position formats within that AX.25
                  packet.

                  Scott

                  Jeremy Day wrote:
                  >
                  >
                  > I guess I should clear up a few things:
                  >
                  > I meant that the GPS input would be NMEA protocol. Output from
                  > the TNC to the radio is (I assume) AX.25 standard.
                  >
                  > Also, by restricted digipeat capability, I mean having the digipeater
                  > listen only for packets from our chase vehicles, which would (I hope)
                  > be the only packets on whatever frequency we chose. This frequency
                  > should be different from the national APRS frequency.
                  >
                  > Thanks to everyone for their input.
                  >
                  > Jeremy Day
                  > Communications Lead
                  > Auburn High Altitude Balloon Team
                  > space.auburn.edu
                  >
                • Bob Burns W9RXR
                  ... In the words of Jeff Foxworthy, you have my attention. Tell us more. How frequency agile will these RF boards be? How much current will they draw? What s
                  Message 8 of 9 , Sep 7, 2007
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                    At 04:25 PM 9/6/2007, Scott Miller wrote:
                    >If and when I get a compact transceiver an all-in-one T2 would be a
                    >possibility. In fact, I'm doing that with the more expensive
                    >commercial 6-watt RF boards.

                    In the words of Jeff Foxworthy, you have my attention.

                    Tell us more. How frequency agile will these RF boards be? How much
                    current will they draw? What's your time line for this project?

                    Bob...
                  • Scott Miller
                    Catching up on email again... The commercial boards will do 136 to 162 MHz in 2.5 kHz steps. Transmitter attack time is under 15 ms. Current drain at 6 watts
                    Message 9 of 9 , Sep 18, 2007
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                      Catching up on email again...

                      The commercial boards will do 136 to 162 MHz in 2.5 kHz steps.
                      Transmitter attack time is under 15 ms. Current drain at 6 watts is a
                      little over 2 amps. Receive current is about 80 mA.

                      They're really not meant for high duty cycles - the PA starts heating up
                      really fast. For testing, I've bolted a couple of the largest TO-220
                      heatsinks I had on hand to the thing and it does much better - I don't
                      have to worry about a software glitch locking it in transmit mode for 20
                      seconds and cooking the board.

                      Scott

                      Bob Burns W9RXR wrote:
                      >
                      >
                      > At 04:25 PM 9/6/2007, Scott Miller wrote:
                      > >If and when I get a compact transceiver an all-in-one T2 would be a
                      > >possibility. In fact, I'm doing that with the more expensive
                      > >commercial 6-watt RF boards.
                      >
                      > In the words of Jeff Foxworthy, you have my attention.
                      >
                      > Tell us more. How frequency agile will these RF boards be? How much
                      > current will they draw? What's your time line for this project?
                      >
                      > Bob...
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