| 摘要 |
PURPOSE:To always cope with change in environmental conditions, by changing the gain of a noise amplifier based on the count value of a counter and setting the squelch level automatically. CONSTITUTION:When a power supply is applied, a power supply reset circuit 17 is operated to reset an up-counter 10 and a down-counter 15. In this case, an output voltage of a D/A converter to which the count value of a counter is inputted is also zero, the gain of a noise amplifier 3 is zero and no squelch output is obtained. After the application of power supply, an oscillation circuit 8 starts oscillation and the up-counter 10 starts counting. Then, the gain of the noise amplifier 3 is also increased and the squelch operation is done. When the squelch operation is started, the down-counter 15 is operated for a prescribed time to fix the gain of the noise amplifier 3 when the count is zero. When the squelch is released, the counter is automatically operated again. |
