| 摘要 |
System for locking the quiescent frequency of colour television sub-carriers, under the SECAM standard. The invention relates to the creation and use of a so-called measurement line in order to employ devices which lock the frequency of sub-carrier oscillators. The arrangement consists of two input routers 4 and 20 to which are applied the modulating signals D'R and D'B at 1 and 18, the other two inputs 2 and 19 are connected to earth or to a predetermined potential. These routers are controlled at 3 and 21 by a signal FL/2. These signals are applied to the sub-carrier oscillators 6 and 23. These oscillators can be rephased by a pip 10 and 27. The sub-carrier leaving these oscillators at 11 and 28 is applied to a new router 12 and 19. This router, controlled by the same FL/2 at 13 and 30, makes it possible to deliver to the outputs 14 and 31 alternately unmodulated lines (measurement lines) and to the outputs 15 and 32 the lines modulated sequentially according to the SECAM standard. The outputs 15 and 32 will be applied to a coupling system 16. The sub-carrier will be available on the output 17 of the coupler. The outputs 14 and 31 of the router (measurement lines) will be used by the locking devices 8 and 25 which are enabled by a signal FL/2 inverted at 8 and 26. The correction voltages leaving the locking devices 8 and 25 will be applied to the inputs 7 and 24 of the oscillators 6 and 23. The present invention makes it possible considerably to reduce the complexity of SECAM locking devices while using complete reference frequency lines. <IMAGE>
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