Device for recording and reading out transponders which move in relation to this device

摘要

A device for recording and reading out information-carrying transponders (T) which move in relation to this device, which device selects transponders which are to be read out according to their distance and is thus unaffected by reflections or unwanted transponder responses from distance zones which are located at a shorter or longer distance. Two phase modulators (PM1, PM2), one of which is disposed in the transmit arm and the other in the receive arm of the read device, are controlled with the same pseudo-random code, although the second phase modulator is time-delayed. Receive signals reflected from a transponder or from other objects are evaluated only if the sum of the transit times of the transmitted RF signal and the signal reflected back to the read device is equal to the delay of the modulation signal fed to the second phase modulator. The device can be used in a stationary manner to read out transponders connected to mobile objects or in a mobile manner, e.g. on trains to read out fixed route markers. <IMAGE>