[aprssig] APRStt Callsign and Checksum

[Matt Murphy]

I didn't understand what the "units digit" but I did some more research and
I now understand it.
(I didn't remember that from math class) The units being the ones place.
Got it now.

Thanks for the help.

73,
Matt Murphy, kc8bew
http://mcares.kc8bew.net
Muskingum Co. ARES EC


On Tue, May 12, 2009 at 14:00, Robert Bruninga <bruninga at usna.edu> wrote:

> > Thanks for the info.  I wasn't it reading
> > right the first time.  I have a further question though.
> > The total for my callsign is 101 like yours
> > so my checksum is 1.  Where do we get 1 from 101?
>
> >> ... You just add up all the keys in the callsign,
> >> and keep only the units digit of the sum.
>
> We will make it clearer in the docs when we get the chance.
>
> Thanks
> Bob
>
> > On Tue, May 12, 2009 at 10:14, Robert Bruninga
> > <bruninga at usna.edu> wrote:
> >
> >
> >       It would be nice if someone would write an APRStt
> CALLSIGN
> >       GENERATOR routine for everyone to use.  They could just
> type in
> >       their callsign, and out comes the DTMF keys to put into
> memory.
> >       This automatically generates the 2-key conversion and
> checksum.
> >       An ON_LINE generator would even be better!
> >
> >       > I have a question about the APRStt checksum.
> >       > What is it and what is it for?
> >
> >       Since the callsign is only entered once into a DTMF
> memory for
> >       easy transmission, we thought it should have a checksum
> to
> >       greatly minimize the chance for errors.  You just add up
> all the
> >       keys in the callsign, and keep only the units digit of
> the sum.
> >       That then is the checksum digit.  If APRStt reecives a
> DTMF
> >       string and the checksum does not match, then there is an
> error.
> >
> >       The APRStt DTMF string for callsigns is:
> >
> >       AcccccccccccVK#
> >
> >       Where V is a user selected overlay byte (or two byte
> letter)
> >       Where K is the checksum (treat ABCD keys as HEX)
> >       Where each letter of the callsign is encoded using the
> 2-key
> >       text system
> >
> >       See www.aprs.org/aprstt/aprstt-user.txt
> >
> >       Bob, WB4aPR
> >
> >
> >
> >
> >
>
>
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