A magnetic field sensor with omni-directional sensitivity

An active magnetic field probe with omni-directional sensitivity has been realized by means of two small active loop antennas and a `90°-hybrid´. The response is flat within 3 dB in the frequency-range from 100 kHz to 8 MHz. The noise floor of the instrument (expressed in an equivalent H-field) is -10 (μA/m) at 1 MHz and 5 dB(μA/m) at the 3 dB cut-off frequencies 100 kHz and 8 MHz. This is sufficient to measure the H-fields at short distance from telecommunication-wiring as the limits for CM-currents are set by CISPR G at 20 dB(μA)