[aprssig] APRStt live demo at Dayton APRS forum (Fri 11 AM)

Robert Bruninga bruninga at usna.edu
Thu May 14 09:56:15 CDT 2015


If you want to participate in the APRStt demo of our next APRS satellite
during the APRS forum at Dayton, pre-load a DTMF memory with your DTMF Grid
and callsign.  (and learn how to send it!).



Im leaving in an hour and will not be able to answer any further
questions.  This is a last minute idea to do the demo…



The DTMF format is: *GGggCCCCCCxxxx#



Where GGgg is your grid, the CCCCCC's represent your callsign spelled on a
DTMF keypad (QZ on key 1) and the xxxx’s represent a binary value that
encodes the position of these letters on each key of the user’s callsign.



For the USA convert the alpha portion of your grid DN=11, EN=12, FN=13,
DM=16, EM=17 and FM=18.  So my grid “FM19” becomes 1819.



For spelling my callsign WB4APR, the CCCCCC keys are 924277.  Now note the
position on each key of the callsign letter.  For WB4APR this is 120112.
Now multiply each of these 6 digits by these binary weights:
1024,256,64,16,4,1 respectively and add them up.  I get 1558 for the xxxx
code for WB4APR.



So my DTMF memory contains *18199242771558# which I put that into my DTMF
memory and every time the satelilte hears it (sent at the slow-auto-rate),
the satellite will acknowledge it with voice: "Grid FM19 from WB4APR" and
it will convert that also to an APRS grid square packet on 145.825 MHz
downlink



If your callsign is shorter than 6 characters, right-pad with spaces (the 0
key and position of 1).



Now also you can send an ARL message using the same technique using this
format: cTMMCCCCCCxxxx# where the “C” DTMF key signals a message, T is any
number but 9, and MM is the ARL message number.  The callsign is the same
as before. If T is “9”, then it is an EMERGENCY.



If you preload these into your radio and TX the DTMF on 144.34 during the
demo (WHEN ASKED) then it might work!  Use your dual band Kenwood or Yaesu
with the APRS side on 145.825 to capture the packets and the other band on
144.34 to send the DTMF and you are ready to go.



Even if you miss the demo, I will hopefully have it at the Byonics Booth
for more demos.



Sorry no time to answer any more questions,  Im leaving now for Dayton…



Bob, WB4APR
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