| 摘要 |
<p>PURPOSE:To adopt a small-sized filter with high reliability by making a frequency applying density modulation to a transmission line signal 1/n (where; n is an integral number >=2) of an assigned monitor frequency to increase the monitor frequency to >=5MHz. CONSTITUTION:The transmission section of a terminal station 1 is provided with a pulse generator 11 generating a pulse train of a pseudo random pattern, a modulator 12 applying a pulse density modulation to its output by a frequency being 1/n of the monitor frequency assigned to each repeater, and a pre-code section 14 pre-coding its output and transmitting the result to a transmission line. Each repeater 3 is provided with BPF28, 28' inputted an output signal of a circuit decoding the pre-code and taking the monitor frequency as the pass band, and a transmission circuit transmitting the decoded pulse train of the pre-code to an opposite transmission line when an output being a prescribed level or over appears at the BPF28. The receiving section of the terminal station 1 is provided with a circuit detecting a discontinuous point in phase as to the frequency component being 1/n of the monitor signal of the received signal.</p> |
