| 摘要 |
PURPOSE:To simplify the titled receiver by detecting the output level of plural receiving frequency convertes to switch surely a low noise amplifier in failure. CONSTITUTION:A circuit supervising a converted output level is provided to receiving frequency converters 27-28 applying automatic gain control respectively to a signal wave branched from a branching device 6 and converting its frequency into a prescribed frequency so as to output an output level alarm signal when the level is decreased less than a prescribed level. A changeover driving circuit 30 is connected to all the circuit output to be supervised and changes over switching devices 2, 5 when the output level alarm signal is received. Thus, even if one set of the converters 27-29 raises the output level alarm signal, the circuit 30 is not activated, and in this case, a converter transmitting the alarm signal is failed and a common use low noise amplifier is normal. On the other hand, if the operation of the amplifier is failed, since input noise is reduced for the amplifier gain's share, all the supervising circuits output an alarm signal to operate the circuit 30. |
