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Re: [aprsisce] Re: Rocket Tracking

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  • James Ewen
    ... Sounds like you still need a bit of clarification... think of it this way, the Kenwood radios have 3 distinct units inside them. There is a radio, a TNC,
    Message 1 of 8 , Apr 25, 2013
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      On Thu, Apr 25, 2013 at 4:15 PM, ajmitchell91 <ajmitche@...> wrote:

      > Thank you James, this clears up a lot of questions we were wondering about.
      > I didn't know exactly what the differences were between the PACKET and APRS
      > TNC's on the Kenwood, but the way you explained it makes a lot of sense.

      Sounds like you still need a bit of clarification... think of it this
      way, the Kenwood radios have 3 distinct units inside them. There is a
      radio, a TNC, and an APRS User Interface. Compare this to one of the
      older traditional packet configurations where you had three boxes, a
      radio, a TNC, and a computer. The radio looked after sending and
      receiving audio over the airwaves. The TNC converted serial data to
      audio, or audio to serial data (modem). The computer ran a program
      that took the serial data from the TNC and displayed on screen, or
      took your keypresses and sent them out to the TNC.

      When in packet mode, the Kenwood radio receives the audio, passes that
      to the internal TNC, and then the serial data is passed out the port
      to an attached computer, plus the opposite direction sending data from
      the computer to the TNC, which is passed on to the radio and sent out
      over the air.

      When in APRS mode, instead of sending the data out the com port, the
      data is passed along to the built in computer, the APRS user
      interface. The packets are decoded and shown to you on the screen. The
      APRS user interface also gathers information from the built in GPS,
      and sends position reports on your behalf as per your settings.

      So generally, you either present the data from the TNC to a computer
      built into the radio, or out a port to an outboard computer. The
      newest generation Kenwood radios however have another special trick
      where you can not only let the APRS user interface parse and display
      the data, but you can also share that data with an external computer.

      The problem here is kind of like having multiple personality disorder.
      There's a bit of a tug-of-war between the built in APRS user interface
      and the external APRS program. Who's in charge? Most APRS program
      assume they are in charge, and you can end up with a bit of a war. You
      have to really understand what's going on to try and ensure that when
      attempting to use this mode, you get stuff set up right.

      > We got it up and running yesterday after I submitted my post by opening the
      > packet log to view the raw packets and then parsing those using a script.
      > We will try out the CTRL-G utility you mentioned which sounds like it would
      > allow us to filter out the other stations while looking at the raw packets.

      The CTRL-G filter test mode will grab just the packets that match the
      filter parameter. You will have to decipher what the packets are
      telling you, and if the packets are mic-e or compressed, you've got
      some work cut out for you unless you have an APRS parsing script like
      the APRS FAP from Hessu and friends.

      > I'd never heard of ICMP packets before, are those the only types which have
      > tracks that can be saved? What kind of devices send that ping?

      I'm guessing you have because you are using the term ping. A ping is a
      specific type of packet used on an IP network. If you go to a command
      prompt and type in PING 64.56.129.2, your computer will send a number
      of ping packets out to that IP address. The server at 64.56.129.2 will
      send responses back, and you will be able to tell how long it took for
      the packet to get to the remote server, and a response to come back.
      There is no ping facility in APRS at all.

      In the APRS world we send UI packets. Those packets are one way only
      packets. There is no response coming back at all. The only time you
      will get an acknowledgement in APRS is when you send a message packet,
      and the recipient station hears that packet. The receiving station
      will send an ack back to let your station know the message was
      received.

      > I guess the confusion we were running into was the difference between a
      > series of waypoints (which is what we are sending right?) and a track.

      Nope, waypoints are specific sentences that get sent from an APRS
      device to an attached GPS. They are usually defined by the NMEA 0183
      $GPWPL string, but there are some proprietary sentences of similar
      ilk.

      The best term to use to describe the packets that get sent from an
      APRS station containing location information is position reports. If
      you use this term, we all know exactly what you are talking about the
      term ping does not apply to APRS (although there are some people that
      use the term erroneously), and a waypoint is a position report that
      has been received by an APRS station, and then translated into the
      NMEA sentence, and is being passed on to a connected GPS device.

      It may sound like semantics, but using the proper terminology can
      ensure that everyone is talking about the same specific bit of
      information.

      > It seemed like to us that since the waypoint packets appear to contain all
      > the relevant positional information, saving to a GPX file was just a matter of
      > formatting. Is there some extra information sent in a ICMP packet that allows
      > GPX files to be created?

      So after all the definitions, we know the above is a little erroneous.

      The BRB device sends a series of position reports which should be
      heard and decoded by the TH-D72, and the serial data passed to the
      computer running APRSISCE/32. APRSISCE/32 will then plot those
      positions on the map for you. How exactly APRSISCE/32 takes those
      position reports and saves them in a GPX file (using the appropriate
      format), I'm not sure of. Lynn might be able to explain.

      There's no black magic in the type of position report being sent, just
      setting up APRSISCE/32 to save the information in a GPX file. I don't
      play with that much though, so I'm not too much help there.


      > I apologize if these questions are silly. We're just a bunch of college kids and
      > somehow it feels like unless you know someone from the previous generation
      > who is a big ham, it's hard to pick this stuff up.

      The questions aren't silly, and I hope that these definitions help
      clear things up a bit and allow us to communicate clearly in the
      future. We can hopefully ensure that we are all talking about the same
      thing at least. It can be intimidating, and appear as if APRS is a
      black art, but it is all simple data communications and computers...
      they only do what we ask, and exactly that. We just have to understand
      what we are asking sometimes.


      James
      VE6SRV
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