| 摘要 |
PURPOSE:To automatically maintain a signal level so as to be a constant level even when the signal level can not be maintained so as to be constant by a normal automatic gain controller. CONSTITUTION:A first automatic gain control loop constituted of a gain adjusting circuit 56, band pass filter 66, and level detecting part 74 or the like is formed at an amplifier provided in the transmission line of the television broadcasting signal and pilot signal of a shared audio-visual facility. The level detection signal of the pilot signal is supplied through the band pass filter 66 and a level detecting part 88 to a status monitor device 92. The status monitor 92 transmits the level detecting signal through a MODEM 98 to a head end side, and a switch 78 in the first automatic gain control loop is switched according to an instruction from the head end side. Then, whether or not the level detecting signal is within a permitted range is judged by a CPU 96, and when it is beyond the permitted range, a control signal is supplied from a D/A converter 100 to the gain adjusting circuit 56 so that the level detecting signal can be within the permitted range. |
