| 摘要 |
1471145 Programme distribution systems COMMUNICATIONS PATENTS Ltd 1 July 1974 [5 July 1973] 32047/73 Heading H4R A subscriber is connected to a desired programme source 1-9 by electromagnetic switches 11-19 each having a plurality of coils 20-37 arranged in different groups requiring coded energization to operate particular switch contacts. As shown the lower coils are seriesconnected into three groups associated with respective thyristors Q1-Q3 and the upper coils form three further groups 21, 27, 33 &c. associated with thyristors Q4-Q6. The TV subscriber presses a reset button (48, Fig. 2, not shown) in his equipment to temporarily remove supply potential to all thyristors Q1-Q6 by breaking a phantom return circuit formed by the programme conductors 40, 41 in his distribution cable 10. He dials a first digit over control line 38, the corresponding charge being transferred from C2 through CY1 and CY2 depending on magnitude and thereby fires a corresponding thyristor Q1-Q3 to enable a corresponding coil group. A second dialled digit is received over line 39 to fire a second thyristor Q4-Q3 and energize a second coil group. The electromagnet whose coils are thus energized connects the selected programme over conductors 40, 41. The programme is HF video and AF and/or HF modulated sound. |
