Random Serendipity

Foundations of Amateur Radio

The other day I was discussing with a fellow amateur the increased frustration my mobile phone provider was inflicting. We hit on the idea of figuring out if other providers would fit the bill and how we could determine if their coverage would suit our needs. Aside from using an old mobile phone, I suggested that using a $25 RTL-SDR dongle would provide a way to record mobile phone cell site beacons from the various mobile networks to map what signal levels we might find.

To that end, I discovered a tool called LTE-Cell-Scanner by Xianjun BH1RXH. Forked from the original project by James Peroulas, it allows you to use simple hardware to scan for LTE Cells used by mobile phone networks. James points out on his site that this tool can also be used to calibrate an RTL-SDR receiver's oscillator, since an LTE downlink centre frequency is stable to within 50 Parts Per Billion, that's 10 times more stable than my Yaesu FT-857d using a TCXO.

If this doesn't mean much, think of it as a local frequency reference standard that you can use in your shack with minimal effort and cost.

The story gets better.

I started building LTE-Cell-Scanner from source and in doing so discovered a directory on my computer named "uhrr". I didn't remember what it was for, so I looked online. The first search result, when I looked for "uhrr radio" was a repository by Oliver F4HTB, more on that in a bit.

The second search result was something called "Universal Radio Hacker". I clicked on the link and discovered a mind boggling tool. There are times in your life when something flips, this was one of those times. It happened when I discovered "csdr" by Andras HA7ILM and again when I discovered "GNU Radio".

Diving into "Universal Radio Hacker", by Dr. Johannes Pohl and Dr. Andreas Noack I was introduced to the art of decoding and generating digital radio signals. In 2018 it was presented for the first time during the USENIX Workshop on Offensive Technologies, or WOOT, as a tool to discover, decode and identify exploits of proprietary IoT devices scattered all over the planet. As an aside, USENIX, Users Of Unix, since 1975.

Back to radio. Universal Radio Hacker allows you to dissect recorded radio signals using all manner of interactive processes. When you go looking for it, and you should, I recommend that you start by watching some videos. You'll find an introductory play list on my YouTube channel. By the time you've seen those, you'll likely share my excitement.

To encourage you further, the Universal Radio Hacker is open source, written in Python, and runs on Linux, MacOS and Windows. So far there have been 94 releases of the software, so it's seen significant development in the years since it was released into the wild.

When installing it I was surprised to discover that its acronym was "uhr", not "uhrr". This was a relief since I still didn't remember what "uhrr" was all about and I couldn't imagine having forgotten Universal Radio Hacker. It turns out that the last time I looked at "uhrr" was apparently in 2021 when I shared my experience in an article titled "The remote edge..."; "uhrr" or "Universal Ham Radio Remote" is a tool that allows you to use a web browser to access a radio remotely.

My little journey into unexpected diversions, distractions and discovery has led me into a path where several puzzle pieces have come together. For example, Universal Radio Hacker and GNU Radio can talk to each other, they're both written in Python, they're both open source, have a history of development and have a community of users. The LTE-Cell-Scanner, also open source, will allow me to calibrate most if not all of my radio gear and I'm once again inspired to keep digging into yet another aspect of this wonderful hobby. I'm sure that there are more than a thousand different hobbies under this roof.

Go forth, explore, discover, be amazed, and stay curious!

I'm Onno VK6FLAB