APRStt Field Guide

K3KDW-12 (HT Symbol) A5B35B3A9A74

+------------------+
| 1    2    3   A  |
|     ABC  DEF     |
| 4    5    6   B  |
|GHI  JKL  MNO     |
| 7    8    9   C  |
|PQRS TUV WXYZ     |
| *    0    #   D  |
+------------------+

The * key is a delimiter between message types and # ends a string. The order of message types does not matter so long as they are separated by a * and the final character is a #

"A" - CALLSIGN (FCC calls, callsign suffixes, or tactical calls)
"B" - POSITION (Requires special configuration and coordination with users to work properly)
"C" - COMMENT (See below)
“D” – MESSAGE (Not currently implemented)

Partially completed transmissions will time out after 5 seconds of inactivity. If you make a mistake just wait and try again.

CALLSIGNs are encoded using the number key and A,B,C, or D to select the position of the desired character. Numbers with no modifiers represent numbers.

SAMPLE CONVERSION: A5B35B3A9A74#
A-Indicates a Callsign will follow
5b        -K
3         -3
5b        -K
3a        -D
9a        -W
7         -“HT” Symbol overlay
4         -Checksum (FOR CALLSIGNS ONLY. The checksum is the last digit of the sum of each character. 0-9 and face value and A=10, B=11, C=12, and D=13)

COMMENTS are initiated by a “C” and terminated with a * if a callsign is next or # if the callsign has already been entered. 0 is a space.
Cnnnnnn* (6 numbers) is a Frequency
Cnnn* (3 numbers) is a Tone

Comments can include the Flintsaw Carrier-PiGeon messaging scheme in place of maidenhead locators or longer comments. (https://github.com/flintsaw/carrier-pigeon)

SAMPLE CONVERSION: C44A444*
C         -Indicates a Comment will follow
44        -Types “H”
A Buttom  –Separates letters using the same input
444        -Types “I”
*         -Ends ends the comment and indicates a callsign will follow


To backcheck your callsign use (https://www.retroscape.com/aprstt/) but we wary that some translators are specifically for Satellite work and don't apply here.
Credit to WB4APR (APRS) and WB2OSZ (Direwolf) for the excellent work that makes this possible!