Author Archive

Radio Direction Finding using KerberosSDR

Traditionally we’ve seen radio direction finding (RDF) in the form of Doppler kits and tone meters, however with the proliferation Software Defined Radio (SDR) we’re seeing a new form of direction finding.

Essentially if you take four software defined radios and coherently link them together, you can then compare the signals from four separate antennas to get a bearing of your target signal’s location.

I recently came across a project on Indigogo which offered this in a complete package called the KerberosSDR. Here is a video of my setup and a demonstration of this radio.

The KerberosSDR is still under development, but from my tests it works fairly well. Unfortunately, I don’t have any traditional RDF gear to compare it to but from what I’ve seen it’s certainly a potential way to go if you’re looking to have some fun with RDF and want some more modern gear.

If you’re interested in the KerberosSDR, you can find more information about it here:

Sending APRS messages to Twitter via the International Space Station

HamRadioTweets is a service that was originally developed and operated by Bruce Sutherland KO4IN. The idea behind his work was inspired by conflicts overseas, it was meant to be a proof of concept on how to get your message out if your government restricts your internet access.

Mr. Sutherland originally created the software as a means to send messages over satellite such as the International Space Station and others that have on-board APRS Digipeaters. I am however getting ahead of myself.

Sometime in late 2014 I had begun learning to write software in ruby, an interpreted programming language, I had quickly found how easy it was to work with sockets allowing me to interact with servers on the internet. I wanted to merge my programming with my love for ham radio. This is when the APRS-IS network came to mind.

I wrote a small ruby gem allowing me to interact with the APRS-IS network, I could see all traffic on the network and filter it in any way I saw fit. Naturally I thought I could add some type of service to the APRS network. There was already a ruby gem that simplified posting to twitter so I figured an APRS to twitter gateway would be a good way for me to hone my new found skills.

After a little research I found that Mr. Sutherland had already developed an APRS to Twitter gateway and even presented it at a computer security conference known as Defcon, However to my dismay I found that it had been offline for some time with what seemed to be no sign of a return. I wasn’t able to find any source code for the software, all I knew was that it had been written in Python.

I thought to myself, if he can write it in Python then I can write it in Ruby. After just two short hours of work I found myself with a simple test server that did exactly what I wanted it to. It would register itself to the APRS-IS network with the callsign designator ‘TWITR’ this would allow anyone from any APRS gateway send a message to twitter by sending it to that callsign.

Later I had contacted Mr. Sutherland and asked him for permission to take over the website and development, which he greatly obliged to and gave me full access to the domain. I began running the server 24/7 on November 23rd of 2014 using the code that I published as an open source project.

The service is back online and available for Amateur use, I plan to continue development in my free time while working on additional services that we could add to the APRS network.

Software Source Code:
Github Repository:

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  • Matt W1MST, Managing Editor