Radio Telescopes Horn In With GNU Radio

Who doesn’t like to look up at the night sky? But if you are into radio, there’s a whole different way to look using radio telescopes. [John Makous] spoke at the GNU Radio Conference about how he’s worked to make a radio telescope (PDF) that is practical for even younger students to build and operate.

The only real high tech part of this build is the low noise amplifier (LNA) and the project is in reach of a typical teacher who might not be an expert on electronics. It uses things like paint thinner cans and lumber. [John] also built some blocks in GNU Radio that made it easy for other teachers to process the data from a telescope. As he put it, “This is the kind of nerdy stuff I like to do.” We can relate.

The telescope is made to pick up the 21 cm band to detect neutral hydrogen from the Milky Way. It can map the hydrogen in the galaxy and also measure the rotational speed of the galaxy using Doppler shift. Not bad for an upcycled paint thinner can. These are cheap enough, you can even build a fleet of them.

This would be a great project for anyone interested in radio telescopes or space. However, it is particularly set up for classroom use. Students can flex their skills in math, engineering, programming, and — of course — astronomy and physics.

We’ve seen old satellite LNAs repurposed to radio telescopes. If you think you don’t have room for a radio telescope, think again.

25 thoughts on “Radio Telescopes Horn In With GNU Radio

    1. A typical 60-70cm ku band satellite dish for television actually has a horn for the feed antenna. Together their primary beam is about a degree wide at 11 GHz.

      A typical SETI horn of plenty at 1420 MHz has primary beam of at least 60 degrees.

      They are not very similar.

  1. It may well be worth having a bit of fun with this especially as herein the UK it’s cloudy most of the time any good stuff is going on ..Take the Lunar eclipse for example….Grr just so very muggy!!!

    1. That’s what I thought when I started too. It turns out radio interference *never* goes away, unlike clouds. Sure, there’s some day/night variation but if you’re in a town it’s usually going to annoy you just as much or more than clouds in terms of ability to observe.

  2. They are using an Airspy R2. Under windows SDRsharp ships with an application called AstroSpy.exe (which I think only works with the Airspy R2, but might also work with the mini as well, not sure). The application collects data over a specified integration time centred around 1420000000 Hz, and can export the collected data to a csv file for further analysis.

        1. One reason that’s possible is because there are enough stations with big power and big antennas to provide contacts with stations of more limited means.

          About 1964, someone organized some time at Arecibo, either before it got completely booked, or maybe under the guise of “testing”. The gain of the dish meant a lot of stations got through, the article I read described it as “like a pileup on 20 metres”.

          But these days there are stations with more than enough gain, so they can work stations with limited antennas, and maybe power.

          It also helps that equipment has improved. 60 years ago, even the best tubes had fairly noisy noise figure, and parametric amplifiers, complicated, finicky and bulky, were the best. You generally needed full power, you had to scrounge and build. There’s a lot more VHF through microwave now, more devices and commercial equipment to make it easier.

          You have to pay, but you can get off the shelf equipment that will only need a power amplifier and maybe a preamp. Sixty years ago, it really meant building a lot of tube equipment, taking up a lot of space.


      1. We (AFRL) did it for fun with a couple hundred watts at 3.5 GHz, but cheated and used a 28 dB antenna (25 foot reflector). We integrated a bunch of 2 second pulses, I forget how long. BTW the moon wobbles a bit, who knew?

    1. Let’s ask the presenter of this video if anyone knows as well as the Australian who works on this system:

      I contacted another person involved and she hasn’t gotten back with me since her reply, Justine Haupt of BNL. I’ll try to contact here again. I’m still waiting on an order for the components for my what I termed Passive Synthetic Aperture Radar… though I might be a little off technically… I have to read into more… however, the systems capabilities will not be limited in regards to capabilities in receiving alone. However, I only intend to receive with the dishes I have for now… though can make a Passive Synthetic Aperture Phased Array Radar also I think with all the dishes systems signals combined and processed that way. Fun with signals processing and imaging algorithms eventually!

    2. Here is a little information… however, the imaging applications aren’t so appearant off the shelf yet. I’ll have to see if I even have any of my old MATLAB data as I think I still have a MATLAB license… though didn’t have the image toolbox though could do some work without if I recall correctly. Maybe R has some open source imaging and I’m sure there are others that I should know about that aren’t coming to mind like Octave. (I don’t see the imaging algorithms however) (I assume the intensity is mapped to create an image based on field of view and positions intensities or something like that)

      Some related resources:

    3. I didn’t read into these in detail yet and will have to read into Hyperspectral Imaging since the data will be available from the system even if using only a specific frequency to map out an image unless time to process doesn’t afford the bandwidth or something I’m not visualizing at the moment:

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.