Turning a Raspberry Pi 2 into a packet station

March 31, 2016

I keep thinking it’s a good idea for emergency communications to have a packet station. Since I’m cheap, I didn’t want to get extra hardware – instead I wanted to use what I had. Luckily, Dire Wolf is better than any hardware packet decoder out there. Here’s how I got a working packet station on a Pi 2 running Raspbian Jessie Lite.

  1. Connect the radio to the Pi. In my case, I had a spare Signalink SL1+ hanging around which made things easier. I  bought a Syba CMedia USB sound card to talk from the Pi to the Signalink, and a Kenwood speaker mic cable to talk from the Signalink to the radio. Here’s a useful hint: the diameter of the wires in the speaker mic cable are roughly the same as the diameter of the wires in regular Ethernet cable – meaning that you can (if you’re careful) strip the outer jacket, put the inner wires in the right places of an RJ-45 connector and crimp direct to them with no soldering at all.
  2. Download and build Dire Wolf. Instructions for doing so on a Pi are here. I mounted my home directory on a networked drive to make life easier.
  3. Configure Dire Wolf with your callsign (I used the SSID -15 after my call) and sound card. Be sure to avoid the “# ADEVICE – plughw:1,0” line – it looks a lot like the correct “ADEVICE  plughw:1,0” line, but takes input from stdin instead of the sound card.
  4. Run “direwolf” and tune the radio to 144.390 (APRS). Make sure you’re decoding packets. You might have to go to alsamixer and adjust input/output. Mine ended up being 51 for speaker, 29 and 12 for mic. Also adjust the radio volume so it’s not too high or too low. (Hit F6 to get your sound card, then F5 to see all devices. I’m not sure which mic I was using; I had two – a stereo and a mono one. The mono one was 29, the stereo one was 12.) It’s probably a good idea to turn off the squelch on the radio as well.
  5. sudo apt-get install ax25-tools ax25-apps
  6. Edit /etc/ax25/axports and set one line to:
    vhf   mycall-15 1200 255 2 VHF link (1200 bps)
  7. Make sure all the other lines in axports have # in front of them (it doesn’t like blank lines).
  8. Run “direwolf -p” to get the KISS port. It will show up as something like /dev/pts/2. Once it’s running, move to another terminal window.
  9. Change frequency to the freq that you’re going to use.
  10. sudo /usr/sbin/kissattach /dev/pts/2 vhf (your IP address in AMPR
  11. sudo /usr/sbin/kissparms -p vhf -t 200 -s 20 -r 64 -l 50 -f n
    These parameters took a little tweaking. If the transmit delay (-t) was too big, things timed out. If it was too small, things stepped on each other. I had to adjust transmit tail delay as well (-l). I found this page useful for some values.
  12. sudo route del -net netmask
    (because I’d set up a route beforehand and needed to nuke it)
  13. sudo /sbin/route add -net netmask dev ax0
  14. ping -i 10 (someone else’s IP who also has a machine on the AMPR net)
  15. Assuming that works, you might want to apt-get install telnet telnetd talk talkd and try to log into your friend’s machine or have your friend log into yours.
  16. Last but not least: I ran into problems with arp. I increased the arp timeout in /etc/sysctl.d/local.conf:net.ipv4.neigh.default.base_reachable_time_ms=1200000