Amateur Packet and APRS

I have had this MFJ-1278 data controller (TNC) for a while now but I haven’t hooked it up. Basically, a TNC connects a ham radio to a computer to allow the transmission of data on the air. By today’s internet standards, it is a bit slow, 1200bps, but packet radio is one of the most flexible forms of data communications around. In the old days, there were a lot of packet bulletin board systems around, there are still a few, but nothing I can find with my temporary setup. The new thing with packet radio is Automatic Position Reporting System (APRS). Basically, a connectionless protocol for communicating GPS coordinates and short messages. APRS is great for coordination and emergency communications, as well as good geeky fun.

I had to make my own cable, well, I could have bought one for $20, but the parts to make it only ran me about $3 and some skill with the soldering iron. Its not a simple cable either, it uses a 5 pin DIN connector on the end that connects to the TNC, the radio end is a little more tricky, the transmit signal and push to talk (PTT) is on the RJ45 microphone connector on the front of the radio and the receive signal is connected to the speaker jack on the back of the radio.




I had some trouble getting the transmit working just right. The TNC would key to transmit, send the packet, but the transmitter would stick on. Not a good situation. It turned out to be poor grounding. The fix was to tape the exposed metal portion of the antenna connector to the chassis of the radio.



It’s been a lot of fun. I tracked a several commuters on their way home from work. I’ve been working on various settings on the APRS software, trying to figure out what is right, I had a lot of trouble to start because I was using some older commands that don’t really work anymore. I’m such a geek, I basically jumped up and down the first time I got a message acknowledged, probably even more so when I saw my station positioned and messages on findu.com