| 摘要 |
PURPOSE:To prevent noise at switching from being caused by applying automatic changeover from a narrow band filter circuit to a broad band filter circuit when a reception signal has a large frequency deviation and evading the circuit from being changed over at each occasion when the broad band filter circuit is once selected. CONSTITUTION:When the frequency deviation of the input signal is large, since the level exceeds a setting value of a mean level detection circuit 36, a switching element 44 is turned on, then a signal of other input of the 2nd NOR gate 53 of a hold circuit 51 is lost and an output appears at the 2nd NOR gate 53. When an output appears once at the 2nd NOR gate 53 of the hold circuit 51 by the 1st switching signal of the switching element 44, since no signal is supplied to one input of the 2nd NOR gate 53, even when the 2nd and succeeding switching signals are sent repetitively, the switching element 44 is not changed over and the hold circuit 51 continues to turn on switching diodes 30, 30 of the broad band filter circuit 23.
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