This paper proposes an advanced detection technique for cable fault by eliminating the sign of reference signal in STDR(sequence time-domain reflectometry) and SSTDR(spread-spectrum time-domain reflectometry). The proposed fault-detection technique can eliminate the reference signal more effectively than the conventional one since the sign detector can approximately recover the distorted reference signal by cable and connector, and consequently, can detect the reflected signal by fault more effectively than the conventional one. Especially, it is shown that the error rate of proposed technique can be significantly lower than the conventional one in the case of far fault simulation.