Abstract: An attack is activated in a receiver amplifier of an interrogator whenever an amplified input signal exceeds an attack threshold voltage value Vatt, and the receiver amplifier at least during a waiting period, the length of which preferrably equals the double length of the longest time interval between adjacent pulses in a transponder data wave packet, after the end of the attack does not respond in the sense of setting the gain. However, the amplifier responds with a decay activated after the lapse of the waiting period, which started when the instantaneous amplified signal value for the last time after the end of the attack exceeded a waiting threshold voltage level Vw. The decay rate is of the same order of magnitude as the attack rate. The improved method for automatically setting the gain renders it possible that the interrogator receiver within the non-contacting identification system practically does not change the essential characteristics of the input signal.

Abstract: In a non-contacting smart card interrogator (1) a first end (A) of an eighth-wave transmission line (13) is connected to a terminal connecting a first receiver (16) to a transmission line (14), and to a second end (B) of the transmission line (14) the carrier wave generator (11) is connected. To the first end (A) of the eighth-wave transmission line (13) the first amplitude demodulation receiver (16) and to the second end (B) thereof a second amplitude demodulation receiver (16′) are connected. In the non-contacting smart card interrogator of the invention an effective use of amplitude demodulation is made possible by changing the phase modulation into an amplitude one by means of a passive element, whereby, however, no noise source has been introduced into the system.