[aprssig] What sets the max packet length for APRS

Steve Daniels steve at daniels270.eclipse.co.uk
Sat Nov 10 12:57:12 EST 2012

There is a handheld radio that will only display 45 character, anything over
that is lost, it's a Yaesu but I forget the model


Steve Daniels


Torbay Freecycle Moderator

APRSISCE/32 Beta tester and WIKI editor http://aprsisce.wikidot.com



From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf
Of Lynn W. Deffenbaugh (Mr)
Sent: 10 November 2012 16:28
To: TAPR APRS Mailing List
Subject: Re: [aprssig] What sets the max packet length for APRS


As I understand the history, there are some radios that won't even display
the 67 characters.  There are/were TNC limits on how long UI packets could
be overall.  Some TNCs can do longer, and the APRS-IS carries a much longer
limit.  But the specification tells you what should work.  Exceeding those
limits may result in unexpected behavior, but as you've observed, there are
lots of packets out there that seem quite long.

BTW, after the colon is the payload.  That particular packet has a
timestamp, position information, weather, and a final comment.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

On 11/10/2012 11:21 AM, Bryan Hoyer wrote:

APRS1.01 states 67 characters for a message and up to 43 for a comment, yet
I see packets twice that long on APRS.FI. This ones 109 after the : 


 <http://aprs.fi/?c=raw&limit=&call=KA8OAD-1> KA8OAD-1>APU25N,
<http://aprs.fi/?c=raw&limit=&call=K8YSE-1> K8YSE-1,WIDE1,
<http://aprs.fi/?c=raw&limit=&call=K8UI-1> K8UI-1,WIDE2*,qAR,
tp://pages.sssnet.com/kend Fairlawn,OH


AX.25 says 256 bytes for the UI payload


A Tweet is 140 characters


An SMS is 160 characters


Is it just the display limit of some radios?


Just exploring the capabilities and limitations of APRS



Bryan Hoyer - K7UDR


aprssig mailing list
aprssig at tapr.org


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