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Re: [tracker2] Re: OT+ and T2 settings for walking in woods (SAR)

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  • Keith VE7GDH
    Robert (callsign?) wrote... ... Actually, if they all heard the original beacon at the same time, they should all digipeat it at the same time... assuming none
    Message 1 of 7 , Sep 26, 2008
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      Robert (callsign?) wrote...

      > It should be unlikely for B, C, and D to all pick the same time to
      > rebroadcast the packet (which would result in the packet getting
      > lost).

      Actually, if they all heard the original beacon at the same time, they
      should all digipeat it at the same time... assuming none of them hear
      another signal on the frequency that would cause it to hold off until
      the frequency was clear.

      If they all held off some random time, you could end up with the
      digipeated packet taking up 3 times as much bandwidth as would
      otherwise be used with all the digis firing off at the same time. As far
      as "who hears what" it depends on the location of the receiving station,
      and the signal strength from the "B, C and D" digis. It is possible that
      a station in the middle of all three digis would not be able to copy
      anything from the digis at all. However, with the nature of FM and
      discriminators and the FM capture effect, it is entirely possible that
      some or even most stations would hear just the digi that was
      strongest at their location. http://en.wikipedia.org/wiki/Capture_effect

      > Additionally, if all the trackers and digis involved have implemented
      > the recommended APRS-specific smart digi algorithms, each digi will
      > rebroadcast the packet several times with increasing delays until it
      > either sees a digipeat copy or replaces the packet with a newer one.

      SmartBeaconing has to do with beaconing at a slower rate at slow
      speeds and at a faster rate at faster speeds, and corner pegging when
      the station turns a corner. Each packet from the originating station is
      transmitted exactly once. However, there is "proportional pathing" in
      the D700 and the Tracker2 has a "NICE" setting.

      > As with everything APRS, your mileage may vary depending on which
      > devices and code you're working with.

      You've got that right!

      73 es cul - Keith VE7GDH
      --
      "I may be lost, but I know exactly where I am!"
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