Packet Radio

Having been curious for a while, I’ve decided it’s time to start properly playing in the world of packet radio. Not just APRS, though - that’s a ‘solved problem’, and quite simple to get a quick hang of.

My main station radio that lives in the hackerspace is a Yaesu FT-7900, and it’s a lovely piece of kit. I’ve got a data cable with proper, separate PTT and audio out/in. It’s got a 9600baud mode as well, so hopefully I can get faster data once all of this has been set up.

All the other radios I easily have access to are Baofeng UV5R or UV6B radios, with no proper data interfaces anywhere to be seen! This made experimentation somewhat more difficult than expected.

As I still find Direwolf easier to deal with than Soundmodem, this was my soft-tnc of choice.

According to the Direwolf manual, the set up should have been fairly simple - section 5.4.2 ‘Linux AX25’. This walks you through setting up an axport description, and running kissattach. On one machine, I ran into problems at this stage, and had to resort to using socat as a work around - section 5.4.2.3. Once kissattach was correctly set up, a route for the subnet was added and ping was attempted.

Because I’ve gained an AMPRNET allocation for Aberdeen & North East Scotland (44.131.6.0/24), I’m using IPs on that range. Specifically, I’m using a pair that’s been allocated to University of Aberdeen for experimentation in this particular example (44.131.6.33 & 34) as the owner was sat beside me, participating in the test. I could have used any RFC 1918 private IP space, (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 or 44.128.0.0/16), but these were the ones that came to mind first.

After a few failed attempts, it became apparent that both radios could hear each other, but because the Baofeng was using vox to transmit, it was transmitting over any response the FT-7900 was giving.

The experiment was semi successful, in that things shouted at each other and heard each other, but there remains work do be done - specifically building a proper soundcard interface for baofengs with GPIO or serial controlled PTT.


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