Comment by radioguy22 9 days ago
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).
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.
I'm super into this idea as a project, can you point me to any design or signal processing info?