Abstract: Apparatus for generating magnetic fields, including a plurality of radiator coils (22, 24, 26) and driver circuitry (30, 32, 33) coupled thereto, which drives the coils so as to generate magnetic fields at a plurality of driving frequencies, wherein each of the plurality of radiator coils (22, 24, 26) generates a field substantially only at a single, respective driving frequency. Preferably circuitry is associated with at least one of the plurality of radiator coils (22, 24, 26) for substantially eliminating magnetic fields generated by the other coils.