| 摘要 |
<p>PURPOSE: To locate the defective block of a transmission line by providing a filter blocking a prescribed measured frequency to each repeater and inserting the filter to the circuit at a designated repeater. CONSTITUTION: A signal from a transmitter is fed to down-stream repeater and receiver from a terminal 18 via an HPF20 and an amplifier 22 from a terminal 16. The signal from the receiver is fed to upper-stream repeater and transmitter from the terminal 16 via an LPF24 and an amplifier 26 from the terminal 18. A cut-off frequency lower than that of the HPF20 is set to an HPF28 to block an external signal intruded from a defective point of a transmission line. A lead relay 30 used as a sequence switch is closed usually and open upon the receipt of a control signal via a decoder 32 to insert the HPF28 to the circuit. The transmitter is provided with a spectrum analyzer or the like to monitor the frequency of the transmission line. When other frequencies than the regular transmission frequency are in existence, the control signal including a code to designate a desired repeater is sent and the sequence switch 30 is open from a repeater remote from the transmitter.</p> |
