PURPOSE: To achieve a shorter measuring time and a better S/N ratio, by displaying a reflection signal returning to an optical fiber input end through an averaging circuit and a signal processing circuit.
CONSTITUTION: A word generator 71 sends a complementary test code to a pulse driver 22 according to an output signal of a timing control circuit 21 of a time area reflectometer. With the driver 22, the test code is converted into an electrical signal and sent to a laser 23 to be injected into an input terminal 25 of an optical fiber 26 through a 3dB coupler 24. A shot allowed for waste time unavoidable following the preciding sequence generates a reflection signal in the optical fiber 26 to be sent to a detector 27 through the 3dB coupler 24. A reseiver 28 amplifies and sends an output of the detector 27 to an averaging circuit 210 through an A/D converter 29, which 210 averages continuous repetition of reflection signal to reduces the S/N ratio. Then, the results of the averaging is sent to a signal processing circuit 72 and a reflection signal generated as one-shot pulse is extracted to be displayed with an output display circuit 211.
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