| 摘要 |
PURPOSE:To detect surely a signal interruption even with a high noise level by e measuring the frequency of a reception signal so as to deciding the interruption based on the continuity of the frequency. CONSTITUTION:A reception signal is fed to a tonal counter circuit 10 via an amplifier circuit 6 and a binary-coding circuit 8. The tonal counter 10 measures the time of one period of the input signal. The frequency of the reception signal is recognized by the time of one period. Then a control circuit 22 to which the measured frequency is supplied compares it with the preceding frequency stored in a tonal data storage area 16. The continuity of the frequency is decided through the result of comparison. When the number of times decided as the presence of continuity is below a prescribed number of times, it is decided as the signal interruption. Thus, the signal interruption is detected surely even if the noise level is high. |
