| 摘要 |
PURPOSE:To attain the reduction of sound volume even if noise or the like are received, by controlling a voice output level by outputs from a circuit detecting synchronization or asynchronization of a received and reproduced clock, and a circuit detecting received electric field strength. CONSTITUTION:A receiver inputs a receiving wave and a demodulating circuit 1 reproduces a clock from the received signal. The reproduced clock is inputted to a phase locking circuit 2 and asynchronization detecting circuit 3 detects the synchronization or asynchronization between the input and output clocks. The circuit 2 is synchronized with only input clocks in a specific frequency range. On the other hand, input electric field to the receiver is detected by an electric field strength detecting circuit 4. Outputs from these two detecting circuits are inputted to an AND circuit 5 and the output level of a voice amplifier circuit 6 is controlled by the output of the circuit 5. Consequently, voice can be reduced even if an unnecessary waves such as noise is received in addition to the absence of a received input, so that highly reliable sound volume control can be attained. |
