| 摘要 |
PURPOSE:To obtain the detected output of a stable SECAM system color discriminating signal even at the reception in a weak electric field by applying limiter and FM detection after inserting a prescribed frequency signal close to a chrominance subcarrier before and after a color discriminating signal. CONSTITUTION:A switch circuit 13 is inserted between an input terminal 1 and a limiter 2, and a signal having a prescribed frequency (4.43MHz) close to the chrominance subcarrier of the SECAM system is inputted to another input terminal 12 of said switch circuit 13. Said switch circuit receives a synchronizing signal from a synchronizing signal input terminal 10, transmits a reception signal from the input signal terminal 1 during the period of the color discriminating signal (c) in a horizontal blanking period, gives a signal H from the input terminal 12 to the limiter 2 during other periods T1, T3 other than the horizontal blanking period, and after the amplitude is limited, the result is detected by an FM detector 3. Since the noise before and after the color discrimination signal is replaced to a prescribed frequency signal and the amplitude is limited, a stable detected output is obtained. |
