[aprssig] APRStt (APRS touchtone DTMF)

Dave Baxter Dave at emv.co.uk
Mon Sep 22 04:15:49 CDT 2008

> > Good questions.  I have tried to get people who know these codes to 
> > provide the best recommendations.  Best we have come up with is to 
> > begin each APRS string with ##A or ##B or ##C depending of the APRS 
> > application.  The ## in many repeaters tells the repeater to ignore 
> > the following tones.  Then two of them improve that probability of 
> > detection.  The A or B or C indicates the type of APRS code to 
> > follow...
> >
> >   
> Guard the repeater control functions with a unique CTCSS tone 
> and a bit of logic.

So, that is going to need one or more visits to the repeater site, and
changing the logic and or firmware then, plus installing other
equipment/software for the voice synthesis etc...

In some territories that will not be permissible, as even a Ham repeater
is licensed based on it's functionality and has to share a commercial
site and reackspace.  Change that, and you'll need to re-apply for it's
licence (and more rack space) and that could signal the end for that box
if other commercial interests get wind of the need for a new ticket.
Good repeater sites are few and far between in many places, and have to
be paid for, some at full commercial rates too.

Even for other places where such changes would be permitted with only a
minor change in paperwork, the cost of doing the changes and gaining the
needed access to the box would be prohibitive for many groups already
suffering rising running costs.  (Site rental, and electricity bill's

Also, if you don't have internet access on site (a cost+ item in many
places, notwithstanding any percieved "network security" issues) how do
you get to/from the APRS network?   If RF, then that's another radio on
site (antenna and licence issues) and the traffic generated could just
tip the local area APRS network "over the edge".   If another site "on
channel linking" to the box (much like IRLP in some cases) then who
stumps up and manages that end of the link.

Then, as if most repeaters don't already have too many Muppets that just
sit there and bleep the things up all the time, we'll get others that
will just forever be sending DTMF codes all day, with no voice ID.
Illegal maybe, but it does happen.

Overall, a nice idea, but please think it through assuming the worst
case user population, and that this list is international in coverage,
not just North America.   Repeaters are a popular tool in Hamdom.  APRS
(sadly?) is a minority interest within the hobby as a whole, whatever
it's benefits might be in some instances.

One last thing...  How to encode a position/status report, from a APRStt
compatible device?  That's going to be a pain to key in if needed.

I'll get me coat...


Dave G0WBX.
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