| 摘要 |
PURPOSE: A device for duplicating a transmission line between an exchange and a base station in a digital frequency shared communication system, is provided to duplicate the transmission line(dedicated line), and to switch a main dedicated line into a spare dedicated line remotely or in a manual operation when the main dedicated line has a fault, so as to minimize service suspension. CONSTITUTION: A spare transmission line is added between an exchange and a base station. An exchange dedicated line switching circuit and a base station dedicated line switching circuit are respectively installed in both ends of a main transmission line and the spare transmission line. In a rectifying circuit(50), a transformer(51) induces a utility AC power, inputted to a first side, to a second side. A bridge diode(52) wave-rectifies the AC power. A smooth condenser(C1) smooths a voltage outputted from the bridge diode(52). A constant voltage(53) makes the current voltage smoothed in the smooth condenser(C1) be a constant voltage(DC12V) and supplies the constant voltage to a next circuit. In a relay driving circuit, an alarm card supplies input power to a next circuit according to a dedicated line switching control signal supplied from a dial modem. A manual switch supplies the input power to a next circuit according to a user's manual operation. A zener diode(ZD) prevents a voltage passing the alarm card or the manual switch from being reversely flown. A light emitting diode virtually displays the state that a dedicated line is switched. A relay circuit is driven with the supplied voltage to switch the main transmission line to the spare transmission line. In the spare transmission line, a wireless interface circuit wirelessly interfaces signals between the exchange and the base station when the dedicated line is switched.
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