APRS SPEC Addendum 1.1


This copy of the APRS SPEC Addendum 1.1 was approved by the APRS-WG. (Vote was called 30 July 2004).
All continuing updates to APRS from that date onward are found on the APRS 1.2 proposed draft addendum.

THE STATE OF APRS as of July 2004: This APRS Specification version 1.1 represents additions, corrections, and deletions since the original APRS1.0 spec of 21 June 2000. This edition represents the state of the APRS protocol and its usage through July 2004. As of this date, the state of the APRS users showed almost 27,000 stations worldwide of which:

  • 33% are fixed or home stations (includes WX stations)
  • 36% are infrastructure (30% digis and 6% IGates)
  • 31% are mobiles

    APRS Mobiles: Of these mobiles, it is interesting to note that almost 60% are transmitting APRS using the Kenwood D7 or D700 APRS radios but more significantly nearly 85% of all mobile APRS users, who view APRS data in their vehicles, use these radios as their only source of APRS data while mobile. Thus, to the extent that APRS is intended for tactical-real-time local display of data to end users, compatibility with these mobile users is a significant driver in the consideration of changes to the APRS Specification. Another interesting observation is that about 55% of all APRS stations are firmware devices (digis, TNC's and trackers and WX stations) that are not easily upgraded. This is a testiment to the stability of the APRS protocol and our desire to maintain compatibility with existing users where possible.

    APRS is NOT Ham Radio's MOBILE COMPUTING: The 1200 baud national APRS user channel cannot and was never intended to be Ham Radio's solution to Mobile Computing . The thousand-fold greater bandwidths required for typical Mobile Computing applications are enormous and there is no attempt to clutter the APRS channel with all possible data that might be of use to a user with a laptop in his car. APRS is for brief, short data types of immediate Ham Radio interest to all tactical users on the local RF channel.

    APRS1.1: With the above as background, the following items represent the uncontested changes, additions, deletions or amplifying information included in APRS Specification Addendum 1.1. There is no intent to re-publish the spec. The original document will remain as is, and these APRS 1.1 revisions will refer back to appropriate pages where noted:

  • APRS-IS Core and Tier-2 servers web pages and how they work.
  • APRS Working Group membership (page 1)
  • Page 25 refers to a 'WPT' NMEA sentence type. Curt, WE7U assumes that should be 'WPL'?
  • The Antenna Gain in the PHG format on page 28 is in dBi.
  • Page 48, 100-109 goes to "u" instead of DEL and 110-179 is 38-107 going to "k" instead of DEL.
  • Updated SYMBOL tables. . But see also all the APRS1.2 proposals for new Symbol Extensions
  • Overlayable Symbols subset. . These were always defined as overlays in the original APRS.
  • Upgrding your symbol set gives background on fixing up your symbol set.
  • JUST MOBILE SYMBOLS: Use these symbols to select only mobile/portable stations for display.
    . . . Primary: '<=>()*0COPRSUXY[^abefgjkpsuv . Alternate: /0>AKOS^knsuv
  • JUST WEATHER SYMBOLS: Primary: _ and W and Alternate: ([*:<@BDEFGHIJTUW_efgptwy{
  • Timeout Old Stations. 80 mins instead of 2 hrs since time-of-receipt to account for stations via satellites (page 10).
  • Symbol Attributes for map displays. (page 92) And Position Ambiguity (p-24)
  • New Overlay Symbols for ARRL and CD symbols. [WinLink]
  • TO-CALLS and Version ID's updated (page 14)
  • Experimental Formats (page 89)
  • DIGI Overlay Characters (new for page 11)
  • Default Paths of WIDE2-2, not RELAY or RELAY,WIDE. (page 11) (updated June 2006)
  • Normally, HID should be OFF in all APRS TNC's (page 91).
  • SSID Conventions in user calls (page 95)
  • DATUM: Standard is WGS-84, but Continental options such as OSG for the UK are OK.(page 21)
  • Range Scale: The standard view size descriptor for APRS displays. ( map example). (page 11)
  • Reply-ACKS Algorithm: Really makes message QSO's FLY! (page 73)
  • Polygon and Line OBJECTS (new for page 31)
  • Halve PHG Range Circles to account for real-world PHG range due to multipath & fading. (page 29) See all about PHG
  • Time Stamps on receipt (page 23).
  • OBJECTS: Amplifying comments on ownership, killing and equality with stations. (page58)
  • OBJECT names should not have any punctuation that cannot be converted to valid Wapoints on most GPS's.
  • AREA Objects are poorly described in the spec. (page 60)
  • Compressed Objects: not recommended for use on RF due to incompatibilities (page 58)
    . . For 1 foot precision, use $GPGGA, or 3rd party compressed posits, or the proposed !DAO! format.
  • ITEM Format is not recommended on RF due to incompatibilities (page 37)
  • Raw Weather Formats not recommended. uProcessors should convert to complete format on RF (pg 62)
  • Weather Details. Amplifying comments on the original spec 1.0. (page 64)
  • The WXSVR Protocols managed by Dale Hugley.
  • AX-25 Table: The AX-25 UI-Frame TABLE lists Flags at the end of a packet being 2 bytes.
    . . The correct number is 1, and it may be shared with the next packet. (From VK2TDS).
  • New WAYPOINT symbol: Red dot (with overlay) marks a mobile's destination. Drawn with a line
    . . between the mobile and its waypoint destination. See example. See description: MOBILE.TXT.

    APRS-IS (Internet System):

  • NOGATE and RFONLY in the RF DIGI field should be ignored by IGates.
  • The Qxx Construct: Marks the source of entry of all packets into the APRS-IS.

    APRS 1.1 SPEC Conventions for the Good of the APRS Network:

  • HF freqs and TNC offsets to help you tune up.
  • APRS Voice-Alert for instant voice contact with any APRS mobile
  • Recommended DIGI paths and striving for network protection ahead of too much user flexibility.
  • Digipeater ID rates for optimum APRS networks
  • NO-ID DIGIS versus ID: All APRS KPC-3+ compatible digis should have UIFLOOD set to NOID
  • D-700 Digipeater Settings are different from KPC-3+ settings (do not use UIFLOOD WIDE,28,NOID).

    The above is the complete APRS 1.1 Spec Addendum. It was a compilation of all the accumulated feedback from users and authors about errata, errors, typos and any omissions in the spec that had been accumulated from the time of the original spec to June 2004. This APRS erratta page had been running continuously for years and was updated whenever these items were discovered and each of these items were widely published and discussed on the APRSSIG and the APRSSPEC working group for public discussion. But it was decided best to finally Freeze the accumulation in June 2004 as APRS1.1 and then after public posting approve it. Then to begin working on any new issues as APRS1.2.

    See the proposals for APRS1.2

    Bob Bruninga, Tech Chariman, APRS Working Group



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