| 摘要 |
PURPOSE:To eliminate the periodic maintenance of a relay broadcasting device by utilizing a high stable frequency signal, such as a chrominance subcarrier, contained in a TV signal, and thus calibrating a local oscillating device. CONSTITUTION:A received TV signal 1 is converted into an intermediate frequency signal through circuit blocks 2-5 shown in figure and the signal is applied to a branching circuit 15. A signal processing part 18 applies a regenerated highly stable signal based upon the chrominance subcarrier, a horizontal synchronizing signal, etc., in the TV signal to a highly stable oscillating device 17 through a gate storage circuit 19 to control the oscillation frequency of the oscillating circuit 17. The output of the oscillating device 17 is applied to the circuit which includes a local oscillation part 7 for controlling a frequency conversion part 6 which converts an intermediate frequency signal into a frequency signal for relay broadcasting, frequency conversion part 11, and phase detector 11, thereby controlling an output broadcasting frequency signal 10. A data processing circuit 20, gate circuit 21, and timing pulse generating circuit 22 detect a period wherein the highly stable signal in the TV signal gets unstable to stop the control over the oscillating device 17 during the period. |
