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[aprssig] Symbol Protocol Help

Robert Bruninga bruninga at usna.edu
Fri Apr 25 14:35:45 UTC 2008


Ev you are right.  There are two ways to refer to any APRS
symbol combination.  One, byt their actual two bytes (which
actually contain many non-alphanumeric characters) or by their
XYZ equyivalents which only use alphanumeric...

There are 95 symbol bytes
There are 38 "table" bytes ("/","\", and A-Z and 0-9)
And that can make as many as 3610 different combinations.

That is all there is to it.

We had refered to those two bytes as "/$" usually... Though we
should probably havc called them "TS" for the TABLE and SYMBOL
bytes

Except that you cannot use many of those original bytes in the
GPSxyz syntax, because those go in an AX.25 CALLSIGN field that
are limited to alphanumeric only.  Therefore we developed a 3
byte way using only alphanumeric characters to represent those
"TS" bytes.  Both sets, the "TS" and the "XYZ" definitions are
listed in the symbol table for each symbol.

Bob

> -----Original Message-----
> From: aprssig-bounces at lists.tapr.org 
> [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Ev Tupis
> Sent: Friday, April 25, 2008 6:11 AM
> To: TAPR APRS Mailing List
> Subject: RE: [aprssig] Symbol Protocol Help
> 
> > 12 "series"
> > (Primary/Alternate, Lowercase/Secondary,
> B????/O????,
> > M????/N????, H????/D????, J????/Q????)
> 
> Thoser are arbitrary nomenclature.  APRS symbol field
> consists only of two bytes.  The second byte is one of
> 95 ASCII symbols. The first byte is either "/", "\" or
> the overlay characters 0-9 and A-Z.
> -----------------------------------------------
> 
> What did I miss?  I can't see where either "/" or "\"
> come into play in the GPS/SYM/SPCxyz portion of the
> protocol.  "/$" and "GPSxyz" appear to be two entirely
> different symbol tables that happen to be mapped at
> the series noted above...or did I misunderstand
> something?
> 
> Btw...I couldn't find any statement that restricted
> GPS/SYM/SPCxyz use to raw NMEA posits only (though
> there's a lot of documentation and I may have missed
> it).
> 
> Kind regards,
> Ev, W2EV
> 
> 
> 
> 
>       
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