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Fixing the 144.39 APRS Network

posted Aug 9, 2013, 7:14 AM by Stones River
Tidbits from http://www.aprs.org/fix14439.html

Executive Summary: If your local APRS channel is not silent say 70% of the time, then it is unreliable for realistic commmunications from most users due to collisions. This page tells you how most areas are limiting hops to 2 hops or less. Some busy areas even limit digipeater response to 1 hop where population density is high and there is an IGate in range of all digipeaters. See how to handle high density areas.

Add a DIGI to your club's 2M Repeater Antenna: N3PX reports it is trivial to add a digipeater to an existing 147 or high-146 repeater to share existing antennas and hardline using an extra duplexer. See how.

SUCCESSFUL APRS: The success of your local APRS is not how many stations you see on your maps, nor how far away, but how reliably your mobile or handheld or portable station can communicate with others in the local area. . There is a big difference and they are mutually exclusive. . This fundamental principal should drive everything we do with APRS in our local areas.


  • Lack of user understanding of fundamentals and severe limitations of such a small channel
  • Too many legacy path options due to obsolete paths making it hard to educate users
  • Too many collisions and lost packets due to too many Hops and too many duplicate packets
  • Software that does not place the health of the Network foremost in the eye of the user
  • Poor Digipeater settings (HID not off, UIDWAIT not 0, and bad packet timing, excessive paths)
  • Improperly formatted packets See live error list as captured on FINDU.COM.
  • Unrealistic user Expectations (expecting to see hundreds of stations for hundreds of miles. Can't happen on RF)
  • Failure to properly set up old PacComm "T" digs (see map) for WIDE2-2 support
  • Continued use of obsolete RELAY and WIDE paths that multiply the number of dupes. see how bad
  • DIGI ROMware that cannot be updated. See my wish list for future digi implementations.
  • Fractionalizing and network disentigration due to local sysop (well intended but inconsistent) hacks.
  • FIXING THE 144.39 NETWORK: The New-N Paradigm not only changes some DIGIpeater parameters but also stresses USER EDUCATION that a local 1200 baud APRS network capacity is greatly reduced by each additional digipeater used. . The area covered goes up, but the capacity is reduced by half. . Typical areas where people use 2 hops with four or more digis, can only support about 60 to 100 or so users in its RF domain. . Conversly, if no digipeaters were used and eveyone could hear each other direct, APRS could theoreticlly support about 360 users on a simplex channel direct (with time slotting). . But because of many people using too many hops and bad paths that cause too many dupes for surrounding areas, some areas of the country are totally saturated with 10 times the amount of attempted packets with only the strongest and most abusive getting through. . Net reliability is miserable for those locals whose packets cannot even get into the local digi due to out of area congestion. . This is self defeating. There are many things wrong:

  • http://www.aprs.org/fix14439.html


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