[aprssig] What sets the max packet length for APRS

Robert Bruninga bruninga at usna.edu
Sat Nov 10 19:21:54 EST 2012

The original texting APRS radio, the D7 can only display 45 bytes of
Messages.  The D700 displays 64.

The VX8R etc I think displays 80 maybe.

Just remember, limiting to 45 charageceters will ALWAYS work and be seen by
everyone.  Anything longer is risking miss-commmunication.

But yes, they can be longer if you KNOW who you are sending to.  That is
why the APxxxx identifies the type of radio in all packets, so we can see
what their capabilities are.


*From:* aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] *On
Behalf Of *Bryan Hoyer
*Sent:* Saturday, November 10, 2012 11:22 AM
*To:* TAPR APRS Mailing List
*Subject:* [aprssig] What sets the max packet length for APRS

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 :

*KA8OAD-1 <http://aprs.fi/?c=raw&limit=&call=KA8OAD-1>*>APU25N,K8YSE-1<http://aprs.fi/?c=raw&limit=&call=K8YSE-1>
,WIDE1,K8UI-1 <http://aprs.fi/?c=raw&limit=&call=K8UI-1>,WIDE2*,qAR,K8LI-1<http://aprs.fi/?c=raw&limit=&call=K8LI-1>
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
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