Abstract: A proximity detection system includes a magnetic field generator for generating a rotating magnetic field having a decreasing intensity over an increasing separation distance, and a magnetic field detector being relatively movable and generating a crossing indication based upon an intensity threshold in the rotating magnetic field being crossed as a threshold separation distance from the magnetic field generator is crossed. The system may also include a transmitter for transmitting a signal relating to the crossing indication from the magnetic field detector. The magnetic field generator may generate a substantially constant amplitude rotating magnetic field vector, and the magnetic field detector may comprise a plurality of orthogonal detection coils. The rotating magnetic field provides a relatively sharp cut-off threshold separation distance defining a perimeter for proximity detection.

Abstract: A receiver for a spread spectrum burst signal having a predetermined period includes a time invariant matched filter for comparing an input signal to at least one reference signal based upon a pseudo-noise (PN) code and providing a stream of data values and a threshold comparator for comparing each of the stream of data values to a threshold to determine an acquisition time for the spread spectrum burst signal. The receiver may further include a contrast filter connected between the time invariant matched filter and the threshold comparator for varying the threshold based upon an interference level to reduce instances of false acquisition detections. Additionally, the receiver may include a window sampler for selectively sampling the data values based upon the acquisition time and the predetermined period.