Configuring Soundmodem TNC in Ubuntu 14.04

Ubuntu 14.04 (and to some extent previous releases) makes the configuration of the soundmodem driver a little more troublesome as the /dev/dsp device is now obsolete.

Below are the steps I’ve just taken to install & run TCP/IP over ax.25 using the Soundmodem driver. Don’t worry, it looks quite complex but 90% is performed in a GUI; the instructions below are the verbose version 🙂

sudo aptitude install osspd (possibly not required)
sudo aptitude install soundmodem
sudo apt-get install ax25-apps ax25-utils ax25mail-utils ax25-tools ax25-xtools
sudo soundmodemconfig
Choose a name (eg. 1200 baud)
Click on chosen config name
Mode: alsa
Audio Driver: Select soundcard channel (in my case plughw:0,0)
– Note: ‘aplay -l’ and ‘cat /proc/asound/device’ can help here
Half Duplex: Yes
Capture Channel: Mono
PTT Driver: None
Click Modulator tab
Mode: afsk
Bits/s: 1200
Frequency 0: 1200
Frequency 1: 2200img_0001
Click Demodulator tab
Mode: afsk
Bits/s: 1200
Frequency 0: 1200
Frequency 1: 2200
Click Packet IO tab
Interface Name: ax0
Callsign: any
IP Address: choose IP
Diagnostics menu can then help with levels
sudo vi /etc/ax25/axports
insert line:
1 YOURCALL 19200 236 2 432.800 MHz (1200 bps)
Save and exit vi
Kill any services which broadcast unnecessarily (samba etc)
Kill auto-discovery daemon (sudo service avahi-daemon stop)
sudo soundmodem &
Check ax0 device, confirm IP config (ifconfig ax0)
Try sending an ICMP packet (ping an address on the ax0 network)

I’ve since discovered most of these steps are covered (with screenshots) at M1GEO’s wiki:-

Useful commands:-

axlisten (dump all incoming packets to console)
axcall (connect to remote station using ax.25)


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2 Responses to Configuring Soundmodem TNC in Ubuntu 14.04

  1. Josh Kearney says:

    What hardware did you use to interface the radio with the soundcard/microphone?

  2. m0spn says:

    Hi Josh – thanks for the comment. At the time of this post I used a cheap ebay USB soundcard, modified with some 1:1 audio transformers for isolation. The Baofeng handie was put into VOX mode which worked *some* of the time. I later discovered issues with this (the Baofeng’s hold the VOX open for too long) but by this point had moved on to other machines/interfaces.

    Circuits can be found online to key the PTT using a serial port. Also, depending on your radio and/or PC you can possibly skip the audio isolating transformers.

    A simple (non isolated but including PTT) interface I made for a different project can be found here:-

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