System zum Sichern einer bidirektionellen Datenübertragung für den Zugang zu einem abgeschlossenen Raum, insbesondere für den Zugang zu einem Fahrzeug

摘要

System comprises an identifying device (C1) with emitting (E1) and receiving (R1) circuits and an identifier (B1). The system includes switches (12,25) allowing a temporary blocking of the emitting circuit connection to the identifier if the distance between identifying device and identifier is less than a pre-set distance. Additionally means for measurement of the resonance frequency generated by the temporary blocking and command means (20) for determining the difference between the measured frequency and a reference frequency are used to maintain the blocking if the difference exceeds a threshold value.