| 摘要 |
PURPOSE:To assure sufficient transmission level and to simplify the circuit constitution, by realizing the function for loudspeaker reception of main trunk and extension hand free response, and assuring suitable reception sound volume to the functions. CONSTITUTION:A plurality of button telephone sets KT are connected to a main device ME with a pair of channels SL and a pair of control lines DL, a hand-set HD is connected to a channel SC of the main device ME, and a changeover relay SR changes over the channel SL to the circuit SC and a coupling transformer T. The output of the transformer T is separated at a hybrid circuit HYB, one is given to a speaker circuit S with an attenuator ATT and another is given to a microphone circuit M. A control circuit KC of the telephone set KT is connected to the control line DL to control the relay SR, the attenuator ATT and the circuit M with a signal from the telephone set KT and a speaker button SK. The functions of the loudspeaker reception of the main trunk and the extension hand free response are realized, allowing to ensure suitable reception sound volume for the both. |
