A cheap and (relatively) easy microwave imager / radiotelescope

I’ve dabbled in radiotelescopes before, mostly as a way to use old TV satellite dishes. However, this time I took a satellite dish and turned it into a microwave “camera”, able to create images in the Ku band!

(Source code for this project is available here)

The dish I’m using is a “Tailgater” model, which is another gadget I’ve experimented with before. The particular model I’m using has a USB console port, allowing serial commands to be sent from a Linux or Windows PC. I was able to automate the motor and receiver commands, driving the dish through a set of azimuth and elevation positions while recording the signal strength.

If you’re planning to do this yourself, these dishes can often be found on Craigslist / Facebook for $0-$50. I think I’ve paid an average of $20 each for four of the things so far. The hard part is finding exactly the right one, as there are various models, revisions, and brand names (VuQube, King, and Winegard are some). Some only have RJ11 control ports, which I haven’t experimented with. The one I’m currently using is from 2014 ,has a square-ish case, and you’ll have to unscrew the top and see if it has a USB “A” port. I’ve also encountered one with a Mini USB port, but couldn’t get that one to work. Update: I dried out the damp Mini-USB version and got a serial console with USB cable. The motors are still seized up, but it seems to be much the same as the USB “A” version. The firmware is from 2011 and doesn’t have an “elangle” command, but changing that to “elev” and changing the numbering range in the python code should theoretically work.

This method is great for imaging a room or building, but where it really shines is for detecting and mapping satellites in geosynchronous orbit. These are, after all, the transmitters this dish is designed for. By panning the dish across the Clarke Belt, I can generate a Ku band image of the radio beacons on these satellites.

These images can be overlaid on panoramic photos to show relative satellite locations. This is a great way to troubleshoot a dish installation (for TV, hobbyist, or other use). You can instantly see which satellites are blocked by trees, or which are drowned out by their outer space neighbors. For example, poor little Galaxy 13 in the 127W orbital slot is barely visible as a dim smudge between the high-power beacons of Galaxy 12 and DirecTV 8. No wonder I had so much trouble picking up PBS on my other dish!

I’m not the first to image satellites like this. Professor James Aguirre of the University of Pennsylvania has a Mini Radio Telescope project on Github. The Thought Emporium on Youtube has a similar project. However, both these approaches require more custom hardware and software for antenna aiming. My method just needs an old $20 Tailgater antenna from Craigslist!

This system can also be used to track down RF leaks. Here’s an indoor scan of my office, overlaid on a panoramic photo of the room. A microwave leak can immediately be seen coming from my poorly-shielded computer tower in the lower right.

If you happen to have one of these Tailgater dishes and want to play around with microwave imaging, check out my Python code at Github. If you’re better at Python that I am, you can probably improve things a bit for your own use 🙂

I’ve also made a video about the project:

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