Comment by tonyarkles

https://scdn.rohde-schwarz.com/ur/pws/dl_downloads/premiumdo...

Passive RADAR is an incredibly cool technology. Instead of the RADAR station transmitting its own signals, it relies on nearby high-power cultural transmissions (FM radio, broadcast TV, etc) as the signal source and measures the reflections of those signals off of aircraft. Since the majority of traffic in the region would be broadcasting ADSB, you'd be able to figure out which tracks from your Passive RADAR system correspond to aircraft without ADSB.