APRS Digipeater With Raspberry Pi, TNC-PI and APRX Software

If you’ve been keeping an eye on my blog you’ve seen I’ve been gearing up to add an APRS digipeater to my local area.

Here you’ll find a quick test and below that a basic how-to on what I did to get it up and running.

Using a raspberry pi, a TNC-PI kit and the free APRX software I was able to get one up and running pretty easily, I wanted to lay out the basics of what I’m using and hopefully help someone out in the process. In my case I just need basic RF digipeating as my tower site does not currently have internet access, although as long as your digipeater is in range of an iGate that is bi-directional it shouldn’t really matter if you have a local internet connection or not. If you do this can be easily added in the aprx configuration.

Below is the assembled TNC-PI kit, you can put it together yourself or simply buy it ready to go. I’d personally recommend the kit, it was a fun build and easy enough for a beginner to assemble with a decent soldering iron.

You can pick one up from Coastal Chipworks here https://tnc-x.com/TNCPi.htm
The kit shipped quickly, although I did have to toss them an email to get my tracking details.

I am using a basic raspberry pi image, the only change was going into the ‘raspi-config’ application and enabling the serial port onboard the pi and selecting the option to disable the serial console login. It’s pretty straight forward and the instructions for doing this are included with the tnc-pi. Those instructions can be found here: https://tnc-x.com/TNCPi.pdf

Once the kit was assembled I needed to build a cable and program my radio, in this case it’s a Motorola CDM configured for external PTT on pin 3. I’m using flat audio with the pin out documentation from the tnc-pi and CDM manuals.

 

All that is left from here is to configure your software with your callsign and get it to boot with your pi.
My config has a basic beacon and the interfaces for the serial port (tnc-pi) as I’m only RF-RF digipeating. However if you want to configure yours to use aprs-is etc the manual can be found here: http://ham.zmailer.org/oh2mqk/aprx/aprx-manual.pdf

First install the needed packages

sudo apt-get isntall aprx ax25-apps ax25-tools -y

Here is my /etc/aprx.conf config file

mycall WB5OD-3

<interface>
serial-device /dev/serial0 19200 8n1 KISS
tx-ok true
</interface>
<digipeater>
transmitter $mycall
<source>
source $mycall
</source>
</digipeater>
<beacon>
beaconmode radio

cycle-size 30m

beacon object “WB5OD-3” symbol “/#” lat “4144.35N” lon “08046.23W” comment “Ashtabula County WideN APRS Digipeater”
</beacon>

It’s pretty simple, just my call for the digipeater followed by an interface block for the TNC-PI, a digipeater block and a beacon block with a basic comment.

Last thing you’ll need is a way to auto-start the application on boot and tune up the rx/tx audio the former is below.

This is assuming you are using a raspberry pi

sudo nano /home/pi/.config/lxsession/LXDE-pi/autostart

at the end of this fill at the following and reboot

@sudo /usr/sbin/aprx

 

To confirm that has worked simply listen to 144.39 or whatever frequency your radio is on, if it worked you’ll hear a beacon with in 30 seconds of application start up, so about one minute after boot.

You could also grep out the active processes and look for aprx running after the pi reboots with the following

ps -A |grep aprx

If you see a process listed then aprx is running.
Hope this was somewhat helpful.

73s

 

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About the Author: KR0SIV

Avid Amateur Radio Operator and Experimenter.