Unfinished How To: Setup the Cross Country Wireless APRS TNC Digi Tracker on Linux

I’ve had my HAM license (SA0BWI) for about 2 years now, and still haven’t really been able to dig in.  Part of it is lack of time, and part of it lack of simple, comprehensive How-To tutorials.

This changes now.

Today (EDIT: this took far longer than a day!) I’ve got the time, tools, and tenacity to figure it out.  In this post, I’ll record the best, quickest, and simplest way to do it, cutting out all the unnecessary detours that lack of experience, knowledge, or guide necessitate for me.


Computer, TNC, and Radio
Computer, TNC, and Radio
  1. Cross Country Wireless APRS TNC Digi Tracker (There are lots of tutorials for the TinyTrack, which is cheaper, but doesn’t, to my knowledge, include a built-in GPS chip.  The Cross Country Wireless device which I have has a GPS chip, a higher price tag, more options, and fewer tutorials for Linux.)
  2. Radio (I use a Baofeng UV-5R).  Having two radios will help – one for working with, and one for monitoring.
  3. Computer (in my case, a Lenovo S10-3s for now, but I plan to switch to a Raspberry Pi sometime in the future – anything remotely modern with a USB port will do.)
  4. Linux (I use Linux Mint XFCE edition.  The commands in this post should work on any Debian-derived distro.)
  5. Cabling to connect your radio to the TNC (custom wiring, you can order it at the same time as the TNC or make it yourself – according to Chris Moulding over at Cross Country Wireless, it needs a 4.7nf capacitor in series with the audio input to the TNC), and the TNC to the computer (USB B to A connector – the same as used by most printers)

Configure the Radio

  1. Set Squelch (SQL in the radio’s menu) to 0 – fully open
  2. Set Transmission Power (TX POWER) to LOW (when you’re done setting everything up, you can change it to high to cover a larger area)
  3. Set Voice Detection (VOX in the menu) to OFF
  4. Set Bandwidth (WN in the menu) to NARROW (May not be necessary, but narrow is the path to the future!)
  5. Set Dual Watch (TDR in the menu) to OFF
  6. Set BEEP to ON (Doesn’t seem right?  May have to do with this bug.)
  7. Set R-DCS to OFF (To be honest, I don’t know if this matters.)
  8. Set R-CTCS to OFF (To be honest, I don’t know if this matters.)
  9. Set T-DCS to OFF (To be honest, I don’t know if this matters.)
  10. Set T-CTCS to OFF (To be honest, I don’t know if this matters.)
  11. Set the radio’s human impersonator (VOICE in the menu) to OFF
  12. Set PTT-ID to OFF
  13. Set BCL to OFF
  14. Set SFT-D to OFF
  15. Set OFFSET to ZERO
  16. Set Squelch Tail Elimination (STE in the menu) to OFF
  17. Set Repearter STE (RP-STE in the menu) to OFF
  18. Set Repeater Squelch Delay (RPT-RL in the menu) to OFF
  19. Set ROGER to OFF
  20. Finally, set the frequency to 144.800 MHz (European APRS frequency)

Configure the TNC

Calibrate the Radio Volume

With the radio connected to the TNC and the TNC ON, increase the volume until the Rx LED glows steady, or almost steady.  You might have to set it at full blast.

Note that I had two different behaviors with my two TNCs: one would glow bright at extremely low volume, and a tad dimmer at moderate to loud volumes; I set this one to a moderate volume.  The other wuold flicker constantly, increasing in brightness with the volume; I set this one to a high volume.

DIL Switches

The first thing to do is set the switches to the right settings.  Here’s what I used during setup:

  1. ON: Radio Port Power
  2. OFF: Selects Terminal Operation
  3. ON: PTT Output
  4. ON: PTT Output on audio (HT-specific)
  5. ON: GPS Receiver (NOTE: You will want to turn this off once we’ve established communication with the device.)
  6. OFF: Not used anyway
  7. OFF: Sets Transmit Audio Level Low
  8. OFF: Digipeater Off

Software Configuration – Minicom

Cross Country Wireless has done a great job with their TNCs, and bundles software for using and configuring them, called APRS Messenger.  There’s only one problem: it’s for Windows.  Yes, there are solutions like Wine, which may or may not work, but I prefer to avoid that.  Therefore, I use Minicom.

Next step is to program the TNC with your callsign and set up other parameters.  To do this, we need to download a serial communication program and connect to the TNC through it.

Plug the TNC into the computer via USB.  I found the instructions over at CyberCiti.biz very helpful to establish the serial connection.  Find out what the COM port device is:

$ dmesg | grep tty

Mine ended up being ttyUSB0

The next thing to do is install minicom:

$ sudo apt-get install minicom

For some reason, the version of mincom that my package lists had was not available on the server, so I had to download the .deb package manually from this URL: http://archive.ubuntu.com/ubuntu/pool/universe/m/minicom/

I followed CyberCiti’s guide to using minicomNOTE: I used sudo because minicom needs write permission to /etc/ to save the configurations we make below.

$ sudo minicom -s -c on NOTE: the -c on is just to make it display with pretty colors, and can be omitted safely.


I went to Serial Port Setup and made the following changes:


  • A: Serial Device to /dev/ttyUSB0
  • E: COM port settings: I changed to 4800 8N1, as recommended by the APRS TNC Digi Tracker Manual, by pressing C B L V W.  Depending on your firmware, you may need 9600 baud.
  • F: Hardware Flow Control: No

On advice of someone over at Texas Instuments, I cleared all the modem and dialing settings.


All that done, I chose “Save Setup As…” and gave the name TNC1.


Then I chose to “Exit from Minicom” as I wanted to run it in a non-SUDO environment.

Re-start minicom with our saved configuration file by running:

$ minicom TNC1 -c on

Note: you may be given an error something like “cannot connect to ttyUSB0″.  If this happens, it’s because your user doesn’t have access to /dev/ttyUSB0, so you need to change the file ownership to give your user access by:

$ sudo chown username /dev/ttyUSB0 (of course, change “username” to your username).

If you are lucky enough, you will be treated to a scrolling list of GPS chip output:


If you’re not so lucky, you might see gibberish instead of the GPS chip outputs.  If this happens, re-edit minicom’s configuration files and change the baud rate.

Now, unplug the APRS TNC Digi Tracker, and change the DIL Switch 5 to OFF.  This will get the GPS chip to quiet down so we can talk to the device.  Plug it back in, and you’ll see something like:


Software Configuration – the TNC

Time to explore the device!  For a quick configuration of all necessary points, run the following commans.  NOTE: you should change some of these when you have figured out that all is working, particularly the beacon timing and beacon text!

You’ll save time by referring to Appendix 2 in the manual, which lists all the commands in their proper syntax.

cmd: mycall SA0BWI-9  (of course, change to your call sign and SSID)
cmd: unproto aprs-0,wide2-2  NOTE:  If you haven’t fully understood APRS Paths, take a look at this video.
cmd: btext >Testing 123...
cmd: beacon every 1
cmd: mon all
cmd: digi on
cmd: myalias wide1-1
cmd: echo on
cmd: txdelay 64
cmd: gps gprmc

Calibrate the TNC Transmit Volume

You should probably do this on an unused frequency, not on the normal APRS frequency.

With everything plugged in, minicom open, and access to the TNC, turn on another radio to monitor.

Put the TNC in calibration mode by using the CAL command in minicom.  You should hear a continuous tone on the monitor radio.

Using a flat head screw driver, play with the potentiometer on the TNC circuit board (almost underneath the GPS) until you find the sweet spot: loud enough to be audible, quite enough to not trigger any peak reduction.

Use the space bar to toggle the tone and find the sweet spot again.  Basically, find a sweet spot that works for both tones, and keep that.

Testing 123…

At this point I wanted to do some testing, just to be sure that I could send and receive packets.  I duplicated the setup with another computer, TNC, and radio, and tried to send messages back and forth using the Converse mode (see the manual).  No luck: sending seemed to work fine, but receiving wasn’t working at all.

I had a call with Chris Moulding, and had feedback from the Yahoo Group https://uk.groups.yahoo.com/neo/groups/cross_country_wireless/conversations/messages/4164

 I’m posting this so that I can share with the group and get their feedback.