| 摘要 |
PURPOSE:To ensure talking equality and a proper volume of dial confirming tone by changing over the side tone volume from the transmission system to the reception system so as to be different depending on the talking and dialing. CONSTITUTION:When a talking signal is generated at an output of a transmission amplifier 4, a processor 14 reads the talking signal via an AD converter 13 and also a side tone signal leaked from a converting circuit 5. The levels of the read talking signal and side tone signal are compared and a constant of a variable balanced circuit network 12 is set variably by the result of comparison so as to minimize the side tone volume. Thus, a prescribed talking quality is ensured and howling is prevented. On the other hand, in detecting that a dial switch 9 is operated, the processor 14 sets variably the constant of the variable balanced circuit network 12 so as to increase the side tone volume. Thus, the dial confirming tone with a proper level is sounded from a speaker.
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