Full Title

Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic or electromagnetic waves, or particle emission, not having a directional significance, are being received (position-fixing by co-ordinating a plurality of determinations of direction or position lines G01S5/00) > using ultrasonic, sonic or infrasonic waves > Systems for determining direction or deviation from predetermined direction > using transducers spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems