| 摘要 |
PURPOSE:To completely prevent malfunction of switching for transmission and reception which is caused in amplifying the received audio signal for ease of listening, by switching the transmission and reception depending on the transmitting level. CONSTITUTION:If a received signal is smaller in comparison with a transnmission audio level, when a sound volume adjusting device of an amplifier 6 is adjusted to a level position larger than a specific level position, an ''H'' level is given to a control terminal 21. Thus, a switch 17 is forcedly turned off, a switching transistor 18 is turned on and a constant bias is given to a reception signal input circuit 11. Thus, since a constant bias is given to the circuit 11 even with the absence of the output of the amplifier 6, if the transmission voice is small, the output of a comparator 13 goes to ''H'' level to switch the mode to the reception. In this case, the transmission switching signal can be kept for a time set at a timer 19. |
