In the amateur radio world, there are various forms of packet radio used throughout the bands. When looking at the higher bands such as 2 meter, as far as popularity goes, the Automatic Packet Reporting System (APRS) takes the cake. It is useful for relaying geographic positions, as well as other telemetry and short messages. It was first developed in the 1980s by Bob Bruninga, a US Navy researcher, and was gradually adopted, and embraced by the amateur radio community.
Because of its early adoption by the amateur radio community, APRS has been incorporated in many models of radio which can make its use by amateurs facile. Initially, APRS communication was facilitated using a Terminal Node Controller (TNC), a special modem like piece of equipment. This allows communication through the use of a computer, and radio, with the TNC acting as a type of intermediary. Because of the limitations of APRS implementations in consumer grade radios, or lack of a built in solution; a TNC, or computer sound card based system can be preferable or necessary.
Having become interested in APRS relatively early on in my amateur radio career, and not possessing any APRS capable transceiver, I purchased a cable meant to interface between my inexpensive handheld radio and the sound card of a smart phone. This however did not yield any useful results. I decided that perhaps obtaining a TNC was the logical next course of action. At the time, the TNCs available either looked ancient, or were far too expensive for my hobbyist tastes. It didn’t help that given recent world events, there was a chip shortage. I decided that a possible avenue would be constructing a TNC from available plans.
After a brief search, I located a promising open source project (MicroAPRS) that I could construct on a solderless breadboard, and which used a microcontroller I had a nice stock of. Because I had all of the components necessary, the only thing I had to lose was some time if things didn’t work.
But things did work, so it was time to get everything off the breadboard, and on to a printed circuit board. The nice thing about this project is that the user has the choice of two different versions of firmware. One uses the KISS protocol which is useful when interfacing with existing APRS software, and the other version incorporates a basic toolbox of commands for a terminal interface, opening the door for many different control options. This TNC has served me well for over a year now, but I am interested in its performance relative to other decoding methods, such as the Dire Wolf project. More experimentation to come.
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