APRS DTMF-to-APRS PROTOCOL                               10 Oct 2002
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                                                              WB4APR

APRStt is the specification for Touchtone applications of APRS.  It
allows anyone with an HT to use his DTMF pad to enter APRS positions,
messages and other data.  Thus EVERYONE in ham radio can communicate
by APRS, not just those with APRS HT's.

Although the Terrestrial application of APRStt with its well defined 
voice repsonses will revolutionize APRS and allow everyone to parti-
cipate, a shortend modified version is necessary for Satellite 
applications.  This is because a satelllite can hear everyone in the
USA or Europe at once.  Thus the ability to combine multiple transmissions
into a callsign, Position, and message is impossible.  The entire
data from one station must be sent in a single 16 digit DTMF string.
This is the typical size of DTMF memories in most HT's.

Therefore the following SPACE version of APRStt is being developed:

FUNDAMENTALS: 
 1) All protocols must fit into 16 digits
 2) All protocols must end with the "D" key
 3) All SPACE protocols must have a valid CHECKSUM
 4) Calls are HASHED, meaning a 6 digit decimal callsign equivalent. 

The best small satelllite application of SPACE APRStt is to have a simple
DTMF decoder on the satellite uplink and then for the satellite to
convert the DTMF to the SPACE-APRStt equivalent AX.25 packet on the
downlink.  Then all APRS stations in the footprint of the satellite and
the worldwide APRS internet linked system of AX.25 receivers will 
receive the data.  If the satelltie is DTMF only, then all it has to do
is regenerate the DTMF on the downlink and let a SPACE-APRStt ground
station convert the packet for injection to the worldwide APRS internet
system.  FOllowing are the initial definitions of SPACE-APRStt formats:

POSITION FORMAT:  The following is the proposed 
 
16 digit DTMF     Packet
----------------  ---------------------------------------
AccccccBhaaalllD  CCCCCC>APxxxx,WIDE:=AAA0.00N/LLLL0.00W$
 
Callsign begins with DTMF "A" and callsign (cccccc) (924277=WB4APR)
Then DTMF "B" indicates POSITION Follows:
    Where h is hemisphere quadrant N,S,E,W and 100's digit of LONG
    where aaa is 3 digits LAT and ooo is 3 digits Long (nearest 10 mi)
Ends with DTMF "D"
 
MESSAGE EXAMPLE:
 
16 digit DTMF     Packet
----------------  ---------------------------------------
AccccccC1234567D  CCCCCC>APxxxx,WIDE::ALL   :1234567
 
Which is a message to ALL from cccccc containing a 7 digit
message.  I have defined MANY pre-defined messages including
ARRL radio grams etc...  so this is not much of a
limitation...