| 摘要 |
PURPOSE: The indoor unit of a communication system having a bypass function is provided to prevent a signal interruption state and to improve the reliability of a system by adding a switching circuit at both ends of a low noise amplifier in an indoor unit to embody an automatic bypass mode in the case of the failure or power supply fault of the low noise amplifier, in a communication system using the indoor unit and a tower-top type antenna unit. CONSTITUTION: A spare amplifier amplifies a signal up-converted at a frequency converter in a base station. A bias-T supplies DC power to each of the blocks of a transmitting unit, including the spare amplifier. A low noise amplifier(23) in an indoor unit compensates line loss by amplifying a signal amplified at a low noise amplifier in a tower-top antenna unit. Another bias-T(24) supplies DC power to each of the blocks of a receiving unit, including the low noise amplifier(23). Switches(25,26) installed both ends of the low noise amplifier(23) executes a switching operation for a transfer to a bypass mode in the case of the failure of the low noise amplifier(23) or a power supply fault from the bias-T(24). A monitoring and control unit(27) detects the status of the low noise amplifier(23) and the bias-T(24) and controls the operations of the switches(25,26).
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