Transponder key reader for use with key reader head, has mixer circuit that transmits modulated carrier and supply current simultaneously on conductors, where carrier is emitted by modem and current is generated by generator

摘要

The reader has a controllable current generator (74) that generates a positive direct current. The generator and a modem (70) are connected to a same pair of conductors (42, 44) by utilizing a mixer circuit (76). The circuit transmits a modulated carrier and a supply current simultaneously on the conductors, where the carrier is emitted by the modem and the supply current is generated by the generator. An independent claim is also included for a system for controlling access to a geographical space protected by a barrier or a door and comprising a transponder key reader and a transponder key reader head.