| 摘要 |
PURPOSE:To improve the hawling of communication equipment, by comparing transmitting signals produced from a transmission microphone with a reference voltage and, when the signals rise to a reference value or above, leaking the transmitting signals and decreasing the gain of the receiving signal transmitting route which drives a loudspeaker for reception. CONSTITUTION:A detecting circuit 16 is provided on the transmission route of transmission signal V1. The detecting circuit 16 detects the level of the transmission signals V1 by means of a comparator 17 by using a reference voltage Vref as a reference. When V1>Vref, the circuit 16 produces a detecting signal Vd and sharply decreases the gain Gv of a 1st amplifier for reception 13. As a result, the level of the voices produced from a loudspeaker 15 is reduced and the infiltration to a microphone 11 becomes small, therefore, no hawling takes place.
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