| 摘要 |
PURPOSE:To decode accurately a complicated code sent at a small pulse interval by controlling automatically the remaining time of a reflected wave at the side of a receiver in orde to set the remaining time of the reflected wave within a prescribed period of time. CONSTITUTION:The arrived ultrasonic wave signal is converted into an electric signal by a transducer 11 and amplified by an amplifying circuit 12. Then a tuning circuit 13 selects only a desired frequency component of said electric signal, and only the signal component is extracted out of the frequency component through a wave detecting circuit 14. This extracted signal component is sent to a code decoding circuit 16 via a waveform shaping circuit 15. Thus the code meaning is decoded. In addition, the circuit 16 measures the remaining reflected waves of the ultrasonic reference signal wave. Then the gain control component of the circuit 12 is decided responding to a correspondence table which is previously set. Thus the gain of the circuit 12 is controlled. The reflected wave is erased when a code signal is received. |
