| 摘要 |
PURPOSE:To detect accurately the start of broadcasting even under an evil effect of fading, etc., by accelerating the time constant of an AGC in a queuing mode and then decelerating the time constant after it is once received. CONSTITUTION:The power supply voltage is always supplied to a high frequency amplifier 2, an IF amplifier 4 and a wave detecting circuit 5 respectively even in a queuing mode. However a relay 15 is turned off, and no power supply voltage is fed to a low frequency amplifier 6. When an emergent broadcast is given for the information of a disaster, etc., an antenna 1 receives it. The received signal is fed to a detecting circuit 12 via the working amplifier 2, the amplifier 4 and the circuit 5. The output of the circuit 12 changes to an H level, and the relay 15 is turned on to actuate the amplifier 6. A high-speed time constant of an AGC circuit is decelerated in a queuing mode. The resistance is increased to a change of modulating degree as well as the fading as the time constant is accelerated. As a result, the broadcast can be detected assuredly. |
