Role of Passive Radar Sensors for Air Traffic Control" at an IEE seminar from June 2006 can be seen here . A recording of a briefing on "PCL Radar Tracking" at an IEE seminar from June 2006 can be seen here . Researchers at Embry-Riddle claiming the use of XM-Radio to detect aircraft can be found here FM radio passive radar using two ultra-low-cost RTLSDR dongles Passive radars Radar Aerial warfare tactics fi:Tutka#Passiivinen tutka