[aprssig] aprssig Digest, Vol 105, Issue 13

Robert Bruninga bruninga at usna.edu
Mon Mar 18 17:43:20 EDT 2013


You raise a good point. However, the use of a checksum makes the added
digit unnecessary.  If any digit is lost, not just the specific one of
your concern, then the callsign fails.

Bob, WB4aPR

-----Original Message-----
From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf
Of Alex Carver
Sent: Monday, March 18, 2013 4:23 PM
To: aprssig at tapr.org
Subject: Re: [aprssig] aprssig Digest, Vol 105, Issue 13

> Message: 3

> Date: Sun, 17 Mar 2013 14:15:24 -0400
> From: Robert Bruninga <bruninga at usna.edu>
> To: aprssig at tapr.org
> Subject: [aprssig] APRStt works!
> Message-ID: <a4dfdc828440c3c490b13ea5bc2172a1 at mail.gmail.com>
> Content-Type: text/plain; charset="windows-1252"
> We used APRStt successfully yesterday to allow anyone with any HT to
> report their positions along our Marathon by entering only the DTMF code
> followed by their callsign from DTMF memory.  The MM number was
> converted by a lookup table to the exact position of the mile mark.
> Further, anyone could report themselves anywere in the 10 mile grid to
> the nearest 600? or so using the DTMF format ?B2XXYY*?
> We think that has great potential to expand the use of APRS at events,
> since everyone in the club could input data, not just the 10% that had
> APRS capability.
> See the web page:
> http://aprs.org/aprstt.html
> More to come when Byonics eventually decides to make these DTMF
> adapters available.  Right now, only 3 of us have alpha models for
> But be thiking of how you can use EVERYONE in  your club at your next
> event to enter data.  For example, how we report Boy Scout troop
> scores at our
> camporees:  http://aprs.org/aprsevent.html
> Our local Repeater owner also said he would be happy to put an APRStt
> decoder on the repeater input so that non-APRS mobiles in the area
> could easily be seen on APRS too?

Bob, I see a bug in your callsign encoding.  You use a single number key
to encode a number but you use a number and then a letter to encode the
letters.  The problem comes when you perhaps lose one of the letter keys
(interference, bad key, etc.) which is then interpreted as a straight
number.  Perhaps you should amend your format such that numbers are
prefixed with 0.  This keeps the 2-symbol-per-character encoding
consistent and also provides a flag for signalling a numeric.

I know that uses up a little bit of  airtime but it isn't much when
talking about the callsign and adds a bit of error checking.

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