Digital signal processor for electronic article gates

摘要

A frequency-swept electromagnetic field is generated in an interrogation zone and signals received from the interrogation zone are processed to detect the presence of a marker with a resonant tank circuit in the zone. Detection is achieved by the use of averaging techniques of a plurality of sweeps wherein peaks above a defined level are stored in a persistence table. A symmetry test is made on the peaks and if the peaks are persistence and symmetrical the presence of a marker is indicated since background noise will not exhibit persistence and symmetry.