28 Jul 2014, 17:36

Simple APRS KK6NXK

Share

APRS is a tactical digital communications system used between amateurs radio, to exchange positions & messages, here I blog my experience decoding/encoding APRS with a small Arduino as it may help some of you too.

Some transceivers are incorporating this functionalities but most of them don’t, a lot of new technicians start with cheap Baofeng radios (30$) which don’t provide advanced functionnalities but here is a way to solve that.

I’ve first looked at Bertos project, a realtime os for micro controllers as Atmel 328p (Arduinos), you can see my 1st attempt there:

This was the receiver only, a simple divider, the “hard” part was to understand the Baofeng/Kenwood mic jacks.

It takes me a long time to figure out that the Baofeng was too slow to trigger the squelch, so the Arduino missed the beginning of the message, hopefully I have a Kenwood too …

So for a Baofeng using this kind of APRS decoder, you have to disable the squelsh completly, and set the volume very high it has to reach a proper signal on the arduino around -3v/+3v.

For the AFSK modulation, the Bertos project use a DAC made with 4 resistors.

Later, I’ve discovered the wonderful work of Mark Qvist MicroAPRS, mostly the same circuit as the Bertos project but with an awesome documentation of the code, it’s a pleasure to read & learn.

So I’ve started to work on a circuit using a Bluno Nano an Arduino Nano with Bluetooth Low Energy, as an iPhone developer, this piece of electronics is just incredible and gives me the capabilites to connect my circuits to iphone Apps.

It’s working but hardly a mobile solution :)

Later I’ve designed a PCB for it you can find the full Gerber files in my Github.

I’m using Frizting to design and then export to OSHPark for the PCB manufacturing, it’s far from perfect but I will improve the circuit and publish it soon !

This plus an iPhone app and you’ll rock APRS !

73 de KK6NXK