| 摘要 |
PURPOSE:To realize a satisfactory hand-free call in calls from both extension and line wire by selecting the balanced network of a hybrid circuit used for the hand-free call in a key telephone system device in accordance with a call distance. CONSTITUTION:The balanced circuit BAC 49 of the hybrid circuit 44 in a hand- free call part is provided with the balanced network (BN) 61 consisting of a resistance R11 for the extension call and a capacitor C11, and the balanced network (BN) 62 consisting of a resistance R12 for the line wire and a capacitor C12 in accordance with the call distance. A selecting circuit SEL 63 which responds to the control of a control circuit CNT 34 operates to select the BN corresponding to the call distance, connects it to the hybrid circuit 44, and attains the stable hand-free call by means of a sufficient sound volume without developing a howling.
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