| 摘要 |
PURPOSE:To attenuate the signals supplied to the speaker from the mike and thus to prevent the howling by detecting the inductive magnetic flux sent from the transmitter provided near the mike through the tuning circuit and then turning on FET. CONSTITUTION:Inductive transmitter 62 is provided near mike 61 connected to external mike jack 11, and the inductive magnetic flux of the frequency slightly out of the broadcast band of the AM radio is emitted from transmitter 62. In case change-over switches 81...85 are switched to the side of contact A, the inductive magnetic flux is detected through the tuning circuit consisting of bar antenna 32 and capacitor 73 from transmitter 62 when mike 61 gets close to speaker 19. And the signal is detected 37 to turn on FET24 via smoothing circuit 91. Thus the signals supplied to speaker 19 from mike 61 are attenuated to prevent the howling. |
