Your Own 11.2 GHz Radio Telescope

Modern life has its conveniences. Often, those conveniences lead to easier hacks. A great example of that is the rise of satellite television and the impact it has had on amateur radio telescopes. There was a time when building a dish and a suitable low noise amplifier was a big deal. Now they are commodity parts you can get anywhere.

The antenna in use is a 1.2-meter prime focus dish. Some TV dishes use an offset feed, but that makes it harder to aim for use in a radio telescope. In addition to off-the-shelf antenna and RF components, an AirSpy software-defined radio picks up the frequency-shifted output from the antenna. There is more about the software side of the build in a follow-up post. We liked that this was a pretty meaty example of using GNU Radio.

A little math predicts that the telescope will see about 1.45 degrees of sky in the half-power bandwidth. Since coax is very lossy at 11.2 GHz, a converter sits right at the feed point and shifts the incoming signal down to about 1.4 GHz. The signal then goes through a bandpass filter, an amplifier, and on to the AirSpy.

As radio telescopes go, 1.2 meters isn’t huge, though you can easily see the sun and the moon transit. The post says you should be able to hear the Milky Way, but that other stellar radio sources may be too faint for the modest equipment.

We see a lot more radio telescope projects these days. Even a relatively small set up can do some things.

24 thoughts on “Your Own 11.2 GHz Radio Telescope

  1. I know that this is probably too small for most stellar objects, but…. If you sweapt it across the sky in a raster pattern could you build up an image that might show those weaker spots as subtle variations between pixels? The noise floor would probably still be too high but it would be cool to try it anyway.

    On that note, anybody know of a good relatively cheap star tracker (that maybe also does satellites for NOAA stuff) that it would be relatively easy to ,punt a directional antenna too? I could build it sure but I’m looking for a bit more reliability then I think I can achieve on my own.

      1. Unfortunately a standard LNB has its own local oscillator, and using a few of them in tandem destroys the phase information in the original signal.

        But if you can find an LNB that takes a reference oscillator to run its PLL, or alternatively if you keep the downlink unmolested (e.g. direct convert to fibre optic as in your first link) then yes, interferometry is possible.

      2. You can also scan very slowly and integrate to get very weak signals, much like photons collected by a CCD. With the processing power of today’s PC’s a bunch of these in proper array of various spacings shold be able to produce spectacular results.

    1. Interferometry ! https://www.eso.org/public/teles-instr/technology/interferometry/
      Get 5000 amateur radio telescopes arround the globe teamed up together in an array managed by interferometry and you could potentially get from that a giant radio-telescope very useful for astronomy scientists.
      Interferometry is a complex science… I’d like to see one day a project led by international astronomy scientists that call for radio amateur people to join-up in building the biggest array of telescopes ever build…

    1. If you want one for “off label” use, best to find a metal one, there’s some plastic ones around that seem to have coating optimised just for broadcast satellite frequencies and they don’t work very well for anything else. Unless you wanna spend an evening gluing tinfoil to it (If you made a mistake, got it free, or just happened to have one)

    2. “I’d love to do Radio Astronomy with one, but I also know I probably never finish the build…”

      I know the feeling. I have four small trough ones and a 10ft’er I need to get commissioned maybe next session. The powers at be don’t like me focusing in on em much.

      I last left off here with some advances slowly like GT2 pulleys and belts for the smaller dishes ( https://www.facebook.com/james.analytic/posts/2815372381857879 ) and more recently for the 10ft dish down here roller casters and PVC pipe cement filled with rebar track for the azimuth assembly… though steel pipe would probably be best since stiffer and not as brittle. Was thinking also just pouring a footing in a base frame on a trailer so would be just a center pivot point and form process to make the track as reinforced concrete entirely. Then using jacks to level and pin footings that can be removed to stabilize.

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