Thanks to Drinas for the link!
An even simpler system that is even harder to counter than a long wavelength search radar is a passive detection system (PDS) that detects and tracks the radio frequency (RF) signals emitted by an aircraft—radar signals, UHF and VHF radio signals, identification-friend-or-foe (IFF) signals, data link signals like Link-16, and navigation transponder signals like TACAN.Info on the Vera-NG here.
A good example of a modern PDS is the VERA-NG, a Czech system being sold internationally that uses three or more receiving antennas spaced well apart to detect and track and identify the RF signals emitted by fighters and bombers. The system’s central analysis module calculates the time difference of the signals reaching the receivers to identify, locate, and track up to 200 aircraft transmitting radar signals. The VERA-NG is only one of many types of PDS used throughout the world: the Russians, Chinese, and others produce PDSs, as well, and these have been widely fielded for several years.
Forgetting the troubled and horribly broken F-35 for a minute. Is this system and others like it "stealth killers"?