Open Source Satellite Trackers: Why Tinkerers Are Obsessed

I still remember the first time I received a signal from space with my own home-built setup. As a lifelong space enthusiast, the idea that I could track satellites and download their data using open-source tools was fascinating and a little unbelievable. Yet here I was, watching data stream in from a weather satellite orbiting hundreds of kilometers above. That moment hooked me. In this post, I’ll share how open-source satellite tracking works, how I got into this hobby, and why so many tinkerers (myself included) are obsessed with chasing signals from the sky.

Liftoff: My First Contact with a Satellite

My journey into DIY satellite tracking began with a mix of curiosity and serendipity. One evening, I stumbled upon an online forum where hobbyists were sharing images they’d captured directly from NOAA weather satellites. These weren’t NASA scientists. They were just regular folks with inexpensive gear. Seeing those grainy but beautiful Earth images pulled straight from space lit a fire in me. I thought to myself, if they can do it, maybe I can too.

I dove in headfirst. I ordered a cheap USB software-defined radio (SDR) dongle (around $20) and cobbled together a simple VHF antenna from spare parts in my garage. With some free software, I aimed to catch a passing weather satellite. My first attempts were glitchy, I got static and garbled lines, but after a few tweaks and waiting for the right satellite pass, I struck gold. An outline of coastlines and cloud swirls slowly materialized on my laptop screen. I had pulled an image straight from a NOAA satellite, and I was ecstatic. It felt like magic that a satellite hurtling through orbit could beam data to my makeshift station. That triumph – hearing the faint signal, seeing the image download line by line got me utterly hooked. I wasn’t just consuming space content; I was participating in it from my backyard.

From there, a hobby turned into a mild obsession. I started tracking the International Space Station (ISS) passes to listen for astronaut communications and slow-scan TV images. I tried decoding telemetry beacons from tiny CubeSats launched by universities. Each new signal was a thrill. Before I knew it, I had a schedule of satellite passes I wanted to catch each day, and I had joined several online communities to swap tips. In the sections below, I’ll explain the technical basics of how this all works and introduce the open-source tools and communities that make it possible for ordinary tinkerers to communicate with space.

How Open-Source Satellite Tracking Works

Satellite tracking at home is possible thanks to open data and open-source software that predict where satellites will be in the sky. It all starts with orbital predictions. Satellites orbit Earth in known paths, which can be described by data parameters such as Two-Line Element sets (TLEs) published by organizations like NORAD. These TLE files are essentially a snapshot of a satellite’s orbit at a given time. Software can take a TLE and propagate the orbit forward to figure out where the satellite will be later on. Modern tracking programs use standard algorithms (like the SGP4 model) to do this math. In plain language: if you know a satellite’s orbit, you can calculate when it will pass over your location, what direction to point your antenna, and even how high in the sky it will appear.

When I started, I had no idea how to do those calculations myself. Thankfully, open-source software handles it. One of the most popular tools is Gpredict, a free cross-platform satellite tracking application. With Gpredict I can load up the TLE data for dozens of satellites and see, in real time, their positions relative to Earth. The software shows a world map with orbital paths and can list upcoming pass times (when a satellite will rise above my horizon). Gpredict leverages the same algorithms used by NASA to predict orbits (SGP4/SDP4) and the publicly available NORAD TLE data to achieve accurate tracking. Essentially, each satellite’s trajectory is computed on my PC so I know exactly when to listen and where to point my antenna.

Open-source trackers like this owe a lot to the pioneers before them. In fact, the hobbyist community has been writing satellite tracking code for decades. (Fun fact: a program called PREDICT, first released in the 1990s, was one of the first open-source satellite tracking engines, and it became the core for many later tools. Even today, PREDICT’s code underpins modern apps like Gpredict!) The spirit of openness means each generation of tinkerers builds upon the last. What used to require juggling printed orbital bulletins and doing math by hand is now handled by free programs with slick interfaces. I simply tell Gpredict my location and load the satellites I’m interested in; it handles the orbital mechanics and tells me “Sat A will be above your horizon at 7:15 PM, coming from the northwest, reaching 45° elevation.” It’s like having a personal NORAD console at home, but open to everyone.

Tools of the Trade: Software, SDRs, and Antennas

So, how does an amateur actually track and receive a satellite? The basic ingredients are: tracking software, a receiver (radio hardware), and an antenna. The good news is there are open-source options for almost every part of this stack.

On the software side, I’ve mentioned Gpredict, which has become my mission control. It not only predicts passes; it can even interface with hardware to automate the process. For example, Gpredict can control radio tuners and antenna rotators through another open-source project called Hamlib. When I got more advanced, I set up Gpredict to automatically adjust my radio’s frequency during a satellite pass to compensate for the Doppler shift (the same effect that makes a train whistle change pitch as it moves – satellites do this to radio frequencies as they zoom by). This blew my mind: the software would tune my SDR in real-time as the satellite flew overhead, keeping the signal centered. I even learned that Gpredict can trigger recordings and track multiple satellites in sequence, so you can queue up observations hands-free. Essentially, these tools let your PC babysit the pass while you listen or watch.

Of course, software alone isn’t enough. You need the ears to hear the satellite. That’s where the hardware comes in, and one of the heroes of the DIY radio world is the RTL-SDR. This is a tiny USB dongle originally made for TV signals, but hackable to receive a wide range of radio frequencies. It’s ridiculously cheap (often under $30) and has become the gateway for many radio hobbies, including satellite tracking. The frequencies many interesting satellites use (for example, 137 MHz for NOAA weather satellites) are well within the range of these cheap SDR dongles. In my case, I started with an RTL-SDR V3, which, paired with free software, became my “space radio.” It still amazes me that a pocket-sized device costing less than a video game can pick up transmissions from orbiting spacecraft.

Then there’s the antenna; the often-overlooked but critical part. You don’t need a giant dish in your backyard; many satellite enthusiasts use homebrew or low-cost antennas. I began with a simple V-dipole antenna tuned for 137 MHz to catch weather satellites. Later I built a directional antenna (a hand-held Yagi made of PVC pipes and metal rods) to better receive weaker ham satellites. Antenna building is a sub-hobby of its own; I’ve seen people create antennas out of tape measures, coat hangers, and even 3D-printed parts. The key is to have something that can receive the VHF/UHF signals most satellites transmit on. Some satellites transmit on higher frequencies (like L-band or S-band), which might require more specialized antennas or low-noise amplifiers, but many popular targets are in VHF/UHF where a simple rig works. The fact that I could build an antenna in an afternoon and immediately start picking up satellite signals was a huge confidence booster – it’s DIY at its finest.

To illustrate how accessible this is, consider the NOAA satellites I mentioned. They continuously broadcast analog weather imagery as they pass overhead. With nothing more than my RTL-SDR and a suitable antenna, I can receive those signals and decode them into actual pictures of Earth. The image above is one of my decoded NOAA images, showing weather patterns over the west coast. The entire setup was controlled by open software: one program tracked the satellite’s position and adjusted for Doppler, while another (a community-maintained decoder) converted the radio signal into an image. This kind of end-to-end chain open-source tracker + SDR + open-source decoder is what makes the hobby so powerful. Everything is in the tinkerer’s hands, and every piece is tweakable.

Tuning In: Receiving Data from Orbit

Tracking satellites is one half of the fun; receiving and decoding their signals is the other. Each satellite is like a little transmitter in space, often sending down data for anyone to hear (sometimes intentionally for ham radio operators, other times just broadcasting to whatever ground station is listening). As a hobbyist, I’m mostly receiving (listening) rather than transmitting – which is good, because listening doesn’t require any license. Once my software tells me a satellite is above the horizon and I point my antenna, I get to tune in and see what’s coming down.

What kind of signals are we talking about? There is a whole smörgåsbord of satellite transmissions out there for the eager listener:

• Weather satellite images: As described, NOAA’s polar-orbiting satellites send analog image signals. When decoded, these show up as grayscale images of Earth with cloud cover – surprisingly high quality for analog. Other weather satellites (like the Meteor-M series) send digital images, which many advanced hobbyists also decode to get color pictures of Earth.
• Telemetry and beacons: Most amateur satellites (including CubeSats built by universities and hobby groups) periodically broadcast telemetry. This might be simple data like battery voltage and temperature, or experiment data from a science payload. For example, I’ve received morse code beeps from a tiny CubeSat that, once translated, contained sensor readings and a call sign. With the right tools, those beeps turn into meaningful data. SatNOGS (the open network I’ll talk more about soon) is especially focused on collecting this kind of telemetry from many satellites – everything from health status to scientific experiment data.
• Voice and repeater satellites: There are amateur radio satellites functioning as FM repeaters in space. If you tune in when they pass, you might hear brief voice QSOs (conversations) between ham operators bouncing their signals off the satellite. It’s a wild experience to hear two people talking via a device whizzing overhead. Sometimes the ISS itself hosts amateur radio events – I’ve listened to astronauts sending Slow-Scan TV images down to us during special events, and even that crackly audio signal gives me goosebumps knowing it’s coming from a spacecraft.
• Experimental signals: Some satellites use innovative communication methods like LoRa or other digital modes to downlink data. For instance, a project called TinyGS has sprung up to allow hobbyists to receive LoRa telemetry from small satellites using very low-cost gear. The variety of modulation and encoding schemes means there’s always something new to try decoding. And because much of this is open, enthusiasts often write and share decoder software for new satellites shortly after they launch.

When I plan to receive a satellite, I use my tracking software to know where and when to listen, then an SDR program (or sometimes a specialized decoder) to actually get the information. It might involve a virtual audio cable piping the sound of the signal into a decoder app. Other times, I watch a live “waterfall” display – a graphical representation of radio frequencies over time – and manually click to tune the signal. There’s something mesmerizing about watching a satellite signal appear on the waterfall exactly when and where you predicted. It starts as a faint line or curve, and if I did everything right, it strengthens to an audible tone or data stream. That’s when the decoder kicks in. For NOAA images I use software (like the open-source WXtoImg program or its modern equivalents) to convert the signal into a picture. For ham satellites, I might use a tool like GNU Radio or dedicated decoders that volunteers in the community have written for that satellite’s protocol.

The payoff from all this tinkering is real, tangible data or images from space in my hands. I’ve built up a little collection: weather images showing tropical storms, text telemetry files from student-built satellites, even a few SSTV images from the ISS. Each one feels like a postcard from orbit, and I got to be the postman. It’s an addicting feeling – which brings me to the community and why many of us just can’t get enough of this hobby.

A Community of Space Enthusiasts

One thing I learned early: no satellite tracker is an island. This hobby thrives on community and collaboration. From online forums and chat groups to global networks of connected ground stations, the open-source satellite tracking scene is a vibrant community of makers, ham radio operators, software developers, and space geeks of all stripes.

A shining example is the SatNOGS project – essentially a community-run mission control center spread across the world. SatNOGS (short for Satellite Networked Open Ground Station) is a global network of satellite ground stations, all built and operated by volunteers. The idea is simple and powerful: anyone can build a ground station (using open hardware designs and software from the SatNOGS community) and connect it to the network. Each station might be a modest setup – a Raspberry Pi, an SDR dongle, and an antenna on a rotator – but when you link hundreds of them, you get near-continuous coverage of satellites around the globe. As a user, I can schedule an observation for a satellite on the SatNOGS network, and some station (maybe on the other side of the world) will automatically record the pass and upload the data to a central database. It’s like crowdsourced satellite operations.

I remember when I first heard about SatNOGS, it sounded almost too good to be true. Here was an open source project that made it easy for people to set up a station and join a global network. They provide detailed guides, 3D-printable designs for antenna rotators, and fully open software to run the station. It started as a Hackaday Prize-winning idea and has grown into a huge community under the Libre Space Foundation. Once I joined, I found myself not only consuming data (accessing the trove of observations in their database) but also itching to contribute. I’ve since set up my own SatNOGS station at home, so when I’m not actively using my gear, it can automatically record satellite passes for the network. It’s rewarding to know that my modest rig is helping, say, a university CubeSat team get their telemetry or a weather researcher collect readings – all without any formal “mission control,” just a bunch of enthusiasts interconnected.

The open-source ethos is strong in these communities. Everything from the circuit board designs for low-noise amplifiers to the code for decoding obscure signal formats is shared openly. If I decode a new satellite, I’ll post about it with instructions so others can do the same. Likewise, I benefit from others publishing their how-to guides and software on GitHub. The attitude is let’s figure this out together. It’s not limited to SatNOGS either; there are smaller communities like TinyGS (focused on low-cost LoRa ground stations) and of course the broader ham radio satellite community (AMSAT), all overlapping. What’s remarkable is that you don’t have to be a licensed radio operator to partake in many of these groups – plenty of members are just tech enthusiasts. In fact, projects like SatNOGS and TinyGS have proven that any techie can build a receive-only space communications station, even if they’re not an official ham operator. That inclusivity has brought a lot of fresh blood into the hobby.

Online platforms play a big role too. I frequented the /r/RTLSDR and /r/AmateurRadio subreddits, where people excitedly share their latest signal catch (“I decoded my first NOAA image!”) or ask for help (“Why can’t I hear this satellite?”). Hackaday’s blog often features cool builds – like an automated rotor made from Arduino or a student who built a ground station in their dorm. These stories inspire others to try, and they definitely inspired me. It’s a positive feedback loop: one person’s success fires up ten more people to attempt it. The community also collectively tracks new satellite launches. Whenever a batch of new CubeSats is deployed (say from the ISS or a rocket launch), hobbyists will be scrambling to identify their signals and update tracking data – it’s like a global scavenger hunt where everyone wins once the satellites are ID’d and added to the network.

Why Tinkerers Are Obsessed

So, why are tinkerers so obsessed with open-source satellite tracking? Speaking for myself, it’s the perfect convergence of challenge, discovery, and community. It scratches so many itches at once:

• Hands-on exploration: This hobby brings space within reach of our own hands. You don’t have to just watch NASA on TV; you can actively receive signals from space in real time. There’s an explorer’s thrill each time you catch a new satellite. For a tinkerer, that direct interaction with orbiting technology is irresistible.
• Endless learning: There’s always something new; a new satellite with a new signal to decode, a new antenna design to try, a new software tool or update to experiment with. The field combines electronics, programming, radio theory, and astronomy. It’s practically a playground for the curious. I’ve learned more about orbital mechanics and RF engineering from this hobby than I ever did in school, because I was motivated by the next “a-ha!” moment.
• Accessibility and openness: The fact that this is all open-source and relatively low-cost means anyone can join. Tinkerers love to modify and improve things, and open-source projects invite that. If I don’t like how a piece of software works, I can tweak it. If I have an idea for better reception, I can build it. There’s no proprietary barrier. This openness extends to data: many of us share our received data freely, contributing to citizen science efforts. That sense of an open frontier keeps the obsessiveness healthy and collaborative.
• Community and impact: As described, being part of a community amplifies the enjoyment. You’re not just tinkering in a vacuum; you’re part of a distributed space program of sorts. And it has real-world impact – students get their satellite data, researchers access more ground stations, emergency communications can be relayed in creative ways, etc. It’s a hobby, but one that occasionally borders on citizen science and public service. Knowing that adds purpose to the obsession.
• The wow factor: Let’s face it, there’s a bit of magic in saying “I built a device that talks to space.” It never gets old hearing the beep of a satellite that I located and tracked, or seeing an image that was in orbit just minutes before. Tinkerers are often chasing that wow factor, the mind-blowing demo or the project that makes the neighbors raise an eyebrow. Satellite tracking delivers that in spades. (Yes, my neighbors have seen me in the yard waving a weird antenna at the sky – they were very confused until I showed them the image I downloaded from space!)

In the end, open-source satellite tracking is more than a sum of its parts. It’s not just the code or the hardware or the data; it’s the experience of bringing all those together to do something that once was considered rocket science (literally!). I often find myself staying up late, waiting for a particular pass of the ISS or a favorite satellite, because I know I’ll get a tiny rush hearing that signal appear. And I know I’m not alone; at that very moment, dozens of fellow hobbyists are out there, laptops and antennas at the ready, sharing the same obsession under the night sky.

If you’ve ever gazed at a passing satellite or the stars and wished you could be a part of that world, I highly recommend giving this hobby a try. With open-source tools, a bit of DIY spirit, and a community to help you along, tinkering with satellites is a thrill that’s surprisingly within reach. Who knows? You might soon find yourself just as obsessed as the rest of us, eagerly counting down to the next pass of something overhead.