| 摘要 |
PURPOSE:To eliminate the need for an independent oscillating circuit and to simplify the circuit by extracting a required carrier wave current from a line supervising current transmitted from a high-order station so as to constitute a redundancy circuit and switching the active/spare devices uninterruptibly. CONSTITUTION:A line supervising current 60kHz transmitted from the high-order station is subject to band extraction 24, only a sinusoidal wave of 60kHz is extracted and subject to A/D conversion at the active and the spare modulating circuits 25, 25' so as to compress level fluctuation. The digital signal is frequency-divided or multiplied at an active or a spare frequency division circuit 26, 26' or synthesized so as to allow a digital signal having a carrier wave supply current component to be produced for a super-group converting section 1, a group converting section 2 and a channel converting section 3 required thereof. A phase comparator circuit 27 detects the phase difference of the digital signal in 60kHz and feeds back it to the frequency division circuits 26, 26'. A switching circuit 28 synthesizes the outputs of the active and the spare devices, a converting circuit 29 applies D/A conversion to the signal and the result is fed to the converting sections 1-3. Thus, no independent oscillator is required, the active device is disconnected without hit if the active device is faulty and the circuit is simplified. |
