A magnetic field excitation and detection coil arrangement is configured to produce an electrical output signal representative of a differential combination of responses from a plurality of magnetic fields, including the field emitted from the excitation coil, a response magnetic field emitted from an object-tagged transponder interrogated by the excitation coil, and other magnetic fields from extraneous sources, such as industrial machinery. This differential combination of the responses from the detection coils will contain only the desired signal (e.g., response from an object-tagged transponder), as the other far away fields cancel, and therefore produces a net output signal level for a downstream signal (transponder output) processor.