[aprssig] Error checking within APRS packets

Keith VE7GDH ve7gdh at rac.ca
Sun Jun 19 14:10:29 EDT 2011

Guido IZ6RDB wrote...

> APRS itself does not carry out any error checking. However error 
> checking is done at the AX25 layer.


> Sounds likely a software problem in the IGate software or a
> problem with the CRC control.

Ah, but the software is UI-View. If it was a bug in the software, 
there would be thousands of stations showing these symptoms.

> The fact that you are reporting the problem happening on several
> packets which are supposedly handled during the same day (rather
> than very rarely), in my opinion excludes the hypothesis presented
> by Bob (of a second packet stepping on top of the original packet,
> producing a "combined packet" which would begin with the first
> original packets and then would continue with the second packet
> and which coincidentally would have the same CRC as the
> original packet).

With all due respect, I would differ from Bob's theory. Although 
unlikely, I might go along with a loose serial cable introducing glitches,
but I would place my money on the TNC, either with PASSALL
turned on or RF getting into the TNC and doing something to the
data after the CRC checking.

Hopefully the iGate operator will be alerted and he will look into it.

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

More information about the aprssig mailing list