[aprssig] Draft Copy of Thesis on APRS

Kenneth Finnegan kennethfinnegan2007 at gmail.com
Wed Dec 10 11:48:22 EST 2014

> *) RF from a local transmitter (could be vhf/uhf/hf) gets into the
> serial cable and corrupts the packet.

I hadn't considered that!

>Also, you mention AX.25 v2.2 in a couple of places, but don't mention
>that most AX.25 implementations stick to version 2.0 of the spec.

I do mention in section 5.1.3 that APRS ignores the digipeater
limitation. I'll try to make that more clear.

>The 3-character minimum limit:  Isn't that for APRS, and not for

Possibly. Since chapter five is discussing AX.25 as it is used for
APRS, I won't make the distinction.

>or as one guy on here
>said, can be morse code

I strongly discourage people from IDing with morse code. It's
important for other users to be able to identify the control operator
for APRS stations in case they are misbehaving, and it is much easier
to find that information if it is included in an AX.25 frame linking
it to the tactical callsign.

>Page 34 talks about not documenting deprecated aliases.

I don't recall if any of the errata actually deprecate all of the
other aliases. I also didn't mention the TEMP or SS aliases, which I
haven't been able to get myself excited about (but that might just be
because I don't see much value in the local NCA alias).

Like everything else I touch on in this thesis, I'd be ecstatic if
someone were to go off and do a thesis on just APRS aliases. :-P

> I didn't see mention of the datum problem

I considered that a Layer 6 (presentation) issue, and steered clear of
it for the sake of brevity (and I also found nothing deficient with
the specification for the !DAO! extension -
http://www.aprs.org/datum.txt )

Kenneth Finnegan

On Tue, Dec 9, 2014 at 3:24 PM, Curt Mills <curt.we7u at gmail.com> wrote:
> Regarding the checksum-on-KISS discussion (pages 25/26/27), there have
> been cases where these things have happened:
> *) RF from a local transmitter (could be vhf/uhf/hf) gets into the
> serial cable and corrupts the packet.  Often we have to re-route
> cables and put ferrites on EVERYTHING to keep the digital
> communications running, particularly with 100W or more HF stations in
> close proximity.  Serial cables make good antennas.
> *) The PC has troubles keeping up with the incoming packets on its
> UART, therefore drops a few characters.  Lack of a checksum can cause
> corrupted KISS packets to be processed.
> --
> Curt, WE7U
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