Abstract: A flux gate magnetometer system utilizes three independent flux gates for measuring the three mutually orthogonal components of the earth's magnetic field. A sensor for each flux gate includes a ring core with a toroidal winding as the drive winding and a differential winding for sensing the difference in saturation due to the earth's flux linkages in the core. The operation of the flux gate magnetometer system is stabilized by a second harmonic servo type null circuit. The output of the differential sense winding is beat with a signal twice the frequency of the drive signal and in phase with the sensor output. This demodulated signal is the error signal for an integration stage. The integration stage drives a high impedance current source which sums into the flux gate sense winding and eliminates the effect of the earth's field in the sensor. An error signal is generated only when the high impedance current source does not null the earth's flux linkages in the core.