Which of the following methods is used to locate sources of noise interference or jamming?

Radio Direction Finding (RDF) is the technique used to determine the directional source of a transmitted radio signal. By using directional antennas and taking bearings from multiple locations, operators can triangulate the exact physical location of a signal source. This method is highly effective for tracking down continuous interference, malicious jamming, stuck transmitters, or even hidden transmitters during recreational 'fox hunts.' The other choices are unrelated technologies: Echolocation is used by bats or sonar, Doppler radar is for weather and speed tracking, and phase locking is a circuit technique for stabilizing frequencies. None of these are used to hunt down a jammer.