Intro
Introduction
The first time I touched a radio was thanks to a friend of my Dad, who after talking over lunch sent me two SDR dongles to play around with. This was the beginning of a fun and educational engineering side gig, it was a way for me to put up small engineering projects with very easily obtainable results, this grew from building a simple ADSB antenna out of copper wire to the more recent works on satellite tracking and ecartometer antenna assembly I have been putting together.
Chapter 01
NOAA QFH
Right from the start I was intrigued by satellites, I wanted to understand better how they worked and what we used them for but more particularly how we could communicate with them. At the time I found out that some NOAA satellites were still emitting APT weather images on VHF bands, which simply put are easier to intercept than regular high frequency transmissions. So I found a paper online on how to build a QFH antenna, it is a pretty artistic design (see the picture) and the idea behind it is that since the satellite is constantly moving, there is always one arm of the antenna that is positioned correctly to get a good read on the signal.
I was able to get some very nice images after a couple of tries and was happy with the results so I moved on to new projects. After some years when I started the electronics program in Bordeaux I was invited to present a project at the Symposium universitaire Radio amateur. This turned out to be the perfect project to showcase and it was an opportunity for me to go back on what I did and dive a little deeper in the theory and see how the whole data chain actually worked.
Download SlideshowChapter 02
Mission Sophie
One gloomy October Thursday night, not long after my arrival at the IUT de Bordeaux I was lucky enough to cross paths with the folks of the F5KBW radio-club, and I unknowingly embarked with my soon to be crewmates on a pretty crazy project, the Mission Sophie.
The picture was simple, they were tasked with setting up the communication infrastructure to guarantee a radio contact with the ISS in the hope of exchanging with Sophie Adenot. They told me they wouldn’t mind a pair of extra hands so I decided to chip in!
For the next seven months the team worked tirelessly on setting up, testing, validating and upgrading the various systems. We had to set up three ground stations, with their own communication channels, antennas and control software.
I was in charge of the software development because we needed a reliable, operator friendly platform. I decided to use Gpredict, an open source satellite tracking software, as a baseline. I laced it with some custom made trajectory optimization logic, automatic rotor and radio linking capability and tested everything to guarantee Windows and MacOS support.
For this I was appointed contact director, my job was to guarantee optimal contact conditions and to coordinate the different stations in case of issues.
We managed to hold the contact for about 11 minutes and asked 18 questions to our favorite astronaut, no technical fault whatsoever, a flawless execution.
At the end of the communication we decided to transmit a big thank you message from the team and the kids and everybody in the room, when I saw the emotion on Ms. Adenot’s face, I started tearing up a bit, at that moment I knew we had done it and it is a memory I’ll keep in a corner of my mind forever.
Chapter 03
F4NAU at F5KBW
After the Mission Sophie, I needed a new project so I thought it would be a great idea to develop my own satellite tracking app with my algorithms so other radio-amateurs can benefit from it too! This is how Skynet was born, I have put to profit the design, engineering and UI/UX optimization I learned at Avini to create a nice looking, handy and intuitive (or at least I hope so :) ) satellite tracking app.
But I wanted to go farther than just building another satellite tracking app because that’s been done before. Right now all the available apps use TLEs (Two Line Element sets). They are text files, kindly provided by NORAD, which contain the computations of the position of satellites at any given time and we can run some simple math to extract the Azimuth and Elevation bearings to point the object while it flies over.
The problem is that TLEs only work for predictable satellite trajectories; you can’t create a TLE for a SpaceX rocket or lunar mission module but you can find a signal coming from the craft and lock yourself onto it. The idea is that thanks to Skynet I have a software platform that I can run some cool experiments on, especially integrating custom hardware like an ecartometer assembly.
The idea is simple, I use a center data antenna to get the signal and around it I include four S-band patches that should allow me to compute the difference in signal strength and tell which direction the signal is coming from relative to my antenna. This way I can create a closed loop system that locks itself on whatever signal it finds. This is in progress but you can find below the design report of the antenna.
Download Ecartometer Report