Designing a Home Radio Telescope for 21 Cm Emission
(arxiv.org)111 points by antognini 8 days ago
111 points by antognini 8 days ago
It's about 14' across. It is in fact a ku-band satellite dish, but these were nowhere near as popular in the UK as they were in the US. I was searching for about 6 months before I found one up for sale.
Page three of the paper shows an enviable rooftop antenna farm. Drool.
I have an ignorant question ... can home/amateur radio astronomy ever produce layperson-appreciated "imagery"? Something easily understood like optical astronomy can produce? e.g. stitching together a sky scan for a particular emission or something?
Yes. But nowing a bit of signal theory, hf electronics and embedded is super helpful.
With 2 antennas you can start playing around with beam forming. This will enable you to scan the sky from one position without moving the antenna. Then you can map the signal strength to a sky projection.
Have a look at the low-frequency antennas from LOFAR. They look like tents for chickens. A lot of them.
It sounds complex and yes.. it's also a bit complex. But still in the range of a project for the home lab.
Yes, in a way.
Think of a single dish radio telescope as a one-pixel camera, where measuring the emission intensity at each point in the sky lets you build up a map. Typically, this is done with high resolution on the frequency axis, which is used to map Doppler shifts for spectral lines of Hydrogen, for example [1].
With a rooftop antenna, it's not likely to be a very sensitive map, though. You'll see the Sun, and its easy to see the Milky Way transit overhead, but other than that ...
The CHIME telescope[1][2] is an example of that.
It's a bit more advanced though, the multiple antennas allows them to "steer" the antenna after the fact through signal processing.
[1]: https://chime-experiment.ca/en
[2]: https://en.wikipedia.org/wiki/Canadian_Hydrogen_Intensity_Ma...
Yep "drift scanning" :)
A single dish/node can't really produce photograph-like imagery akin to an optical telescope, more often[1] you get something like in the setileague website hits [2].
[1] Where by "more often" I mean "once in a blue moon".
I've just started learning about radio comms. I'm using the ARRL Handbook for Radio Communications 101, which is great so far.
My main goal is to detect the hydrogen line, or maybe some distant/noisy object (can amateurs pick up pulsars?). I also want to understand antennae much better, and maybe make a wire fractal antenna. I have a crazy idea about making a 3D fractal antenna-making bot from Lego or something! :D
(I'm not under any illusions about whether a fractal antenna is "better" but I just like the idea of them)
> (can amateurs pick up pulsars?)
In theory, yes but it's supposed to be pretty tricky. Since it looks like you're up for making antennas, maybe this is for you:
https://britastro.org/wp-content/uploads/2021/03/SmallApertu...
Vela is the "brightest" pulsar but is only visible in the southern hemisphere. B0329+54 is the "brightest" in the northern hemisphere.
Optical astrophotography has stacking software. Radio astronomy has a counterpart in folding software.
Thank you for the link! A pulsar or something "noisy but distant" in space is my goal, I think. The idea of being able to listen to distant stars is mind blowing to me, just amazing stuff.
Start detecting signal reflections from airplanes.
With multiple synchronized receivers you can build a passive radar.
Single reflections can easily be spotted by just staring at the spectrum (Doppler).
I'm super into this idea as a project, can you point me to any design or signal processing info?
For room-scale passive radar, search HN for IEEE 802.11bf and WiFi 7 Sensing.
Have a look at this (and other repos/website) https://github.com/30hours/blah2
There are a lot of open source projects. And technology (algorithms and receivers) wise it isn't too complicated nor a secret. That stuff is almost 100 years old.
An easy start is always looking at VHF reflection of strong transmitters that are not creating a lot of noise (like FM stations). ILS or VORs stations are classics.
There are also a lot of meteor and space radars ( https://en.wikipedia.org/wiki/GRAVES_(system) ). Universities are super happy in publishing very very detailed (https://www.iap-kborn.de/en/research/department-radar-remote...) specs of their sky radars. And frequencies are well known for ages.
The german Wurzberg radar system (https://en.wikipedia.org/wiki/W%C3%BCrzburg_radar) was used after the war to help discover the hydrogen line.
The RTLSDR is a great tool. But signals really be bandpassed (what the guy in the paper did) because its dynamic range is limit to only 8 Bit.
Some pics of the OG detector from the 50s https://www.radio-astronomy.org/node/368
The Purcell mentioned is the same one of NMR Nobel and E&M textbook fame.
Amateur radio astronomy has a storied history.
I had a dish set up in London, 20 years ago (before I came out to the USA). Looked like #1. The dish splits into segments, and I recall driving down the M1 from Birmingham in my battered old Ford Escort, with the (razor-sharp) mesh segments squeezed in and wobbling right next to my jugular... Those dishes were getting vanishingly hard to find in the UK, so it was worth the trip, and I kept my neck intact with only minimal damage...
I had it all packed up when moving out to the US (because my imagination told me that houses in the US were far larger than in the UK). The house I ended up buying (despite having a much larger back garden) didn't have the space to set it up again and remain married, so two decades later, it's still in that wooden case... I do, however, have an optical telescope set up (#2)
Back then, we didn't have easy access to SDR's, so there's a feed horn, a down-converter, and I had an external (standalone) WinRadio receiver to actually listen to the feed. That went into an audio card on a linux box, and the waterfall display was beautiful :)
#1: https://imgur.com/a/CDrEeII
#2: https://imgur.com/a/askar-130phq-scope-sb-myt-mount-26mp-cam...