| 摘要 |
<p>PURPOSE:To improve an S/N by using the alternating code for which the polarity inversion is executed by a certain frequency as the supervisory and controlling signal. CONSTITUTION:A light relay T2 is controlled from a terminal station T1 through a down optical fiber cable 31. The control signal inverts and modulates an alternating code S11 generated by an alternating code generating device 32 with a polarity inverting circuit 34 at a frequency fc designated by a coder 33. An inverting modulation signal S12 is applied to a laser diode 35, comes to an optical signal L3 and arrives at the T2. At the relay T2, a light receiving element 36 receives and converts the signal to an electrical signal S13, the signal S13 is reproduced by a reproducing relay circuit 37 and a data signal S16 and a cock signal S14 are obtained. The signal S14 is frequency-divided by FF38, an alternating code S15, the signal S16 and the code S15 are inputted to an 'or else' circuit 39, thereby obtaining the square-wave output of the frequency fc. By passing this through a BPF 40, the frequency (fc) is extracted, and by a detecting device 41 and a decoder 42, a control circuit 43 is driven. The system can be applied to the supervisory system of the digital transmission line.</p> |
