Making an AX.25 Modem

During my last quarter at UCR, I took a project-based embedded systems class. The majority of our time outside of class had to be spent working on some project of our own design that incorporated embedded systems. I decided to use that opportunity to incorporate my amateur radio hobby in some way.

I have pretty terrible mic fright, so I typically use my ham license to work digital modes. The mode that caught my interest for this project was APRS.

For the first project deliverable, I worked on a transmitter that would upload GPS position fixes to the APRS network. For the second half, I implemented demodulation on the modem and used it to make a simple AX.25 bulletin board server. This was my first serious attempt at digital signal processing, and I learned a lot having to work within the limitations of the MSP430.

As part of the class, I had to make videos explaining my work for each component, so I’ll let myself do the talking: