PURPOSE: To make a transponder recognize a starting signal from an interrogator without any mistake and return a starting response signal only on the basis of the starting signal from the interrogator.
CONSTITUTION: A signal inputted to a starting response signal receiving circuit 38 is inputted to a filter means 36A for passing a signal of a prescribed band containing the frequency of a starting signal and a timer means 36B is operated by the signal passed through the filter means 36A, while the number of pulses of the signal passed through the filter means 36A is counted by a counter means 36C. When a transponder invades into a communication area of an interrogator when a CW wave or a data signal wave is transmitted, a stepped signal is inputted to the transponder and this stepped signal is passed through the filter means 36A and counted by the counter means 36C. Since this signal has a stepped form, however, the number of pulses counted by the counter means 36C is only one and consequently no starting response signal is returned from a transmission means. In the case when the starting signal is inputted, on the other hand, the number of pulses counted by the counter means 36C is in a plurality, and therefore the starting response signal is returned from the transmission means.
TANAHASHI IWAO
ENDO CHISATO
ISHIKAWA SOICHI
OKUDA TAKEHIKO
TOYOTA MOTOR CORP
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