| 摘要 |
PURPOSE:To prevent howling and to amplify the quantity of received sounds by turning on an electronic switch when the transmission sound quantity is smaller than a reference value to eliminate a variable attenuation circuit from the reception circuit and turning off the electronic switchn when larger than the reference value to insert the variable attenuation circuit into the reception circuit. CONSTITUTION:When a comparator 18 decides it as during talking, an electronic switch control circuit 15 outputs a L signal and in other cases, a H signal is outputted. When the electronic switch control circuit 15 outputs the L signal, the electronic switch 13 is turned off and when the circuit 15 outputs the H signal, the electronic switch 13 is turned on. When the electronic switch 13 is turned off during talking, a reception sound volume variable resistor 12 is provided to the reception circuit and the reception sound volume is provided to a receiver 4 after being subjected to losses comprising a resistor of the variable resistor 12 and a variable attenuation circuit comprising a resistor 14. When the electronic switch 13 is turned on during not talking, the variable resistor 12 is eliminated from the reception circuit and the signal enters the receiver 4 without any loss.
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