a magnetic encoder is disclosed that provides a uniform magnetic field which is time modulated at a carrier frequency and space modulated by a repetitive pattern of eddy - current conducting lands that move with variable motion . the time modulation is provided by driving an electrical coil in a resonant tank circuit . the space modulation provides areas of higher and lower magnetic field intensity which change in correspondence with the motion of the conducting lands . the intensity of the varying magnetic field is detected by a series connected pair of stationary coils that are positioned orthogonal to both the direction of the changing magnetic field and the direction of the motion of the conducting lands . the pair of stationary coils yield a differential electrical signal that is representative of the motion of the conducting lands .