| 摘要 |
PURPOSE:To keep the AGC operation with the same degree as the preceding operation, even when one frequency is interrupted, by transmitting a plurality of pilot frequencies at all times. CONSTITUTION:When one of pilot frequency sources PF1, PF2 is interrupted, an output level of band pass filter BPF is rapidly lowered by 3dB, because the power is halved. This state is detected at a level detector DET and the gain of a DC amplifier AMP2 is controlled to restore it to the orginal state and the level is restored to the preceding value. The entire time constant of the AGC circuit is set longer so that the main signal level of the transmission line is not fluctuated. When a failure of a pilot frequency source is restored, the output of the amplifier AMP1 is increased for a short time. The gain of the amplifier AMP2 is lowered after the detection with a level detector DEC. |
