Czech technical university - 2018 - https://www.radioeng.cz/fulltexts/2018/18_04_1155_1165.pdf https://www.radioeng.cz/fulltexts/2018/18_04_1155_1165.pdf But c

Czech technical university - 2018 - https://www.radioeng.cz/fulltexts/2018/18_04_1155_1165.pdf https://www.radioeng.cz/fulltexts/2018/18_04_1155_1165.pdf But concepts are translatable to other technologies, for example mobile phone network signals (even without decrypting it) which in most populated areas can have hundreds frequencies by itself. there are literally literally thousands of radio signals around us which can be used for various unintended / non-cooperative purposes. also not only ground based signals, satellites are transmitting all kinds of signals towards earth, some for communication, some for remote sensing / earth observation. Or not only is it possible to use non-cooperative signals for timing, but also for passive radar. For example DVB-T - you receive bounces/echoes of signal from airplanes, drones and measure its characteristics. NATO public document - UAV Detection and Localization Using Passive DVB-T Radar MFN and SFN - https://www.sto.nato.int/publications/STO%20Meeting%20Proceedings/STO-MP-SET-231/MP-SET-231-18.pdf https://www.sto.nato.int/publications/STO%20Meeting%20Procee... Good community is around GNURadio, they have all kinds of enthusiast and profesional usecases, explorations, videos, ... Or just simple 30$ RTL-SDR + laptop, you can sit next to road and listen for tire pressure monitoring sensors data, they contain unique ids, so you can know when postman enters your street...