Radio transponder

摘要

A transponder adapted to be used in a checkout or inventory control system is arranged to transmit by modulating and re-radiating a transponder signal frequency derived from a carrier frequency received on a transmitting antenna. The transponder includes a dual mode antenna (L4) and circuitry (18) which selectively operates the antenna (L4) to suppress undesired emission of the transponder signal frequency when the transponder is not transmitting. A terminating circuit (22) is provided which suppresses undesired emission of the transponder signal frequency by a demodulator portion of the transponder. <IMAGE>