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16775Re: [tracker2] Macro issues OT3m

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  • Scott Miller
    Aug 16 10:35 PM
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      I think I should just hire you to do all of my customer service, James!  You're beating me to all of these. =]


      On 8/16/2014 9:45 PM, James Ewen ve6srv@... [tracker2] wrote:

      From your recent posts on this forum, it looks like you're very new
      into APRS and and still have some very idealistic concepts about how
      this is all supposed to work. I used to be just like you... give me a
      little while, and I'll try and beat this optimism out of you. If I
      succeed, I might be allowed to join the "club".

      On Sat, Aug 16, 2014 at 9:23 PM, owenvk@... [tracker2]
      <tracker2@yahoogroups.com> wrote:

      > "Digipeaters are supposed to immediately grab the channel and digipeat what
      > they heard."I have noticed in my recent exploration of APRS that digis tend to
      > "immediately grab the channel", and I am sure some lightweight thinkers have
      > put forward rationale for this...

      Well, the primary "lightweight thinker" behind this concept is Bob
      Bruninga WB4APR, the guy that invented APRS.

      Have a Google for APRS packet fratricide. Bob's concept is that
      neighbouring digipeaters are SUPPOSED to intentionally interfere with
      each other, and in doing so, they stop packets from propagating over
      large distances. It's a ridiculous idea, and to attempt to be able to
      make it work, you have to expend a great deal of time and effort to
      find locations for digipeaters that would allow such a concept to

      I've butted heads with Bob a number of times over basic concepts like
      this. I put forth a concept to Bob back in 2002 about dynamic
      digipeating that would limit the packets digipeated based on the
      number of packet digipeats being requested, and the distance of the
      source station. That was dismissed as being bad for APRS because of
      the "randomness and unpredictability" of the digipeating of packets.
      Yet this packet fratricide concept is deemed to be APRS nirvana.

      > but for example, there are two WIDE digis on very prominent hills. both within 20km of my
      > home and can be heard for hundreds of km... and when they both "immediately grab the
      > channel", they interfere with each other and you are unlikely to decode either of them.

      Hey, sounds familiar, huh? That's how APRS is "supposed to work".
      Packet fratricide is working perfectly.

      > It is one of the contibutions to low success rates in getting posits to a remote iGate that hears both digis.

      But, by design this is EXACTLY how the digipeater network is supposed
      to work. Bob's suggested solution is to put a yagi on the i-gate so
      that it receives one digipeater stronger than the other. By getting
      one signal stronger than the other by a large enough margin, the FM
      capture effect will allow for a successful packet decode.

      Your local digipeaters are not installed properly to be able to
      support digipeating in the APRS network. One or the other would need
      to be relocated so that you don't get the overlap where you see the
      collisions. Yes, that's a pain in the backside, and it is very
      difficult to find locations where you can get the digipeaters set up
      to provide unique coverage, yet still be able to talk to the
      neighboring digipeaters, and also have excellent RX/TX coverage where
      it can hear those low powered trackers and other stations, and be
      heard by them as well with minimal holes in the coverage.

      I've argued this point for over a decade, and it falls of deaf ears.
      We have built a digipeater network of over 30 digipeaters here in
      Alberta, and they don't follow the intentional interference concept.
      Our digipeaters wait for a clear channel. This means that packets take
      slightly longer to propagate through the network (They are only 2 or 3
      hops max), but the packets make it through the network reliably. We
      also support the SSn-N concept, and have tested using AB7-7 numerous
      times. I can reliably get 5 hops across the province. I can't get
      further because 5 hops crosses the whole network!


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