APRS iGate setup with minimum hardware – part 4

It’s been a while since the last update. Let’s wrap this topic up by going through the final set-up for the minimum hardware (= soundmodem based) iGate.

Part 1 lists all the needed building blocks for the iGate. PC, linux/ubuntu operating system, soundmodem software, xastir software (aprs client), internet connection, 2m FM radio (only RX is needed for iGate) and an audio (stereo) cable with 3,5 stereo plugs are needed.

Part 2 shows how to configure the xastir for the connection to APRS-IS server. In this case there is no GPS, but your station location is entered as part of the station configuration. This makes sense for a fixed station, especially for an iGate.

Part 3 shows how to configure the soundmodem. When this is done it might be a good idea to test that the soundmodem works properly. This can be done with the soundmodemconfig’s Diagnostics functionality.

Connect the 2m FM radio audio to PC mic input with the audio cable. Turn on the radio on the aprs frequency (in Europe 144.800 MHz). Click Channel 0 and choose Diagnostics-Modem. You will get the following screen:


Every aprs packet received will produce two rows of information. If you see this, then you are half way there. Your soundmodem setup is capable of acting as TNC and able to decode aprs packets.

Close the soundmodemconfig by File-Quit to save the configuration.

Now comes the tricky part. Because of the way soundmodem and xastir handle the ports the easiest way to countinue would be to start also xastir as root, but due to security issues it would be not a good idea. It’s better to change the user rights of xastir. This is done by typing

sudo chmod 4755 /usr/bin/xastir

in the terminal window. Now you can start xastir as a normal user. Note: the path (/usr/bin/xastir) is valid for Ubuntu 12.04. Please check where xastir is installed in your distribution.

Next step is to add soundcard modem as a new interface to xastir. So start xastir and choose Interface-Interface Control. Click Add and choose Serial KISS TNC. You will see the following window:


 TNC Port is /dev/soundmodem0 and Port Settings 1200 bps. In iGate Options enable the option Allow RF to Inet traffic ONLY (other options are disabled). In KISS Parameters enable the option Init KISS-mode on startup. Click OK. Now the Interface Control window should look like this:


 You are almost there! Now start soundmodem by typing in terminal window

sudo soundmodem

If you don’t get any error messages, go back to xastir Interface Control window and click Start All. DOWN text should change to UP on both devices. If that’s the case, then your iGate is up and running. Congrats!

Next part will describe how to monitor the iGate traffic to make sure everything works.



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