Ultra-sensitive magnetic field receiver capable of operating in high noise environments

The present invention relates in general to object geolocating and tracking systems of the type described in U.S. patent to Belcher et al, U.S. Pat. Nos. 5,920,287, and 5,995,046 (hereinafter referred to as the '287 and '046 patents, respectively), assigned to the assignee of the present application and the disclosures of which are incorporated herein, and is particularly directed to a reduced complexity, non-modulated AC magnetic field communication scheme. This non-modulated AC magnetic field communication scheme includes a ('demodulatorless') magnetic field detector, which is readily coupled with a tag transceiver unit, and responds to a narrow-band, non-modulated AC magnetic field used to communicate with the tag when the tag comes within a prescribed proximity of a tag-programming magnetic field generator. The unwanted influence a noise-source environment upon a modulated (e.g., FSK-encoded) magnetic field-based communication system is diminished by a non-modulated AC magnetic field communication scheme that uses a demodulatorless magnetic field detector. When installed in a tag to be tracked by a geolocation system, the demodulatorless detector responds when the tag comes within a prescribed proximity of the field generator producing the non-modulated AC magnetic field. The received signal is downconverted to baseband and processed to detect a valid AC magnetic field tone and indicate whether the tag is within a prescribed proximity of the AC magnetic field source.