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Comment by bloopernova | Hacker News Reader

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)

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> (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?

A lot of passive radar stuff is ends up export controlled so open source is sparse here

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.

Have a look at this (and other repos/website) https://github.com/30hours/blah2

For room-scale passive radar, search HN for IEEE 802.11bf and WiFi 7 Sensing.

https://github.com/Marsrocky/Awesome-WiFi-CSI-Sensing

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