| 摘要 |
PURPOSE:To get rid of a fact that the other calling party becomes entirely silent, and to prevent anxiety for setting a channel, by setting a loss value inserted into a transmitting line, in case when a calling party of a loudspeaker- telephone set is executing a call, to the extent that a room noise, etc. can be transferred to the other calling party. CONSTITUTION:On each of a transmitting line by a microphone 1 and an amplifier 2, and a receiving line by a loudspeaker 12 and an amplifier 13, variable losing circuits 5, 15, and auxiliary variable losing circuits 21, 25 are provided. A difference of the respective output levels of these circuits 5, 15 is derived by a differential amplifier 23, is compared with a reference value by the respective comparators 22, 24, in accordance with which is larger, the transmitting signal level or the receiving signal level, and in accordance with a result of its comparison, the auxiliary variable losing circuits 21, 25, etc. are controlled. In this state, in accordance with an output of the amplifier 23, a level of a high gain amplifier 8' is set, and when a calling party is not calling, a loss value inserted into the transmitting line is set to the extent that a room noise, etc. can be transferred to the other calling party, and anxiety for setting a channel is prevented. |
