| 摘要 |
1306366 Wired broadcasting COMMUNICATIONS PATENTS Ltd 21 May 1970 [22 May 1969] 26200/69 Heading H4R In a wired broadcasting system a subscriber is connected to a central programme source by two pairs of lines. One pair is used for the transmission of programmes from the source to the subscriber and for the transmission of power to a programme selector control at the subscriber station while the other pair is used for the transmission of signal from the programme selector control at the subscribers station to a programme selection apparatus at the central programme source. As shown the central station apparatus includes a number of highways 7 over which respective television programmes are available. A selector mechanism is provided for each subscriber controlled, e.g. by a dial mechanism, to connect a desired programme to each subscriber. The unbalanced programme sources on highways 7 are converted to feed balanced lines 5 leading to the subscribers by transformers 20, 25 with the power to operate the programme selector supplied from battery 27 in a phantom circuit arrangement using both conductors 5. At the subscribers station a dial mechanism 45 to 49 is arranged to supply pulses of current from the phantom circuit on lines 5 to one of lines 6 to cause stepping of the programme selector switch 16, 17 from a datum position to a position where it selects a desired programme, while a switch 51 is provided to supply current to the other line 6 to energize a pulse generator 30 at the central station which returns the stepping switch to the datum position. The sound signals are applied at audio frequencies from terminals 9 and the video modulated on a carrier from terminals 11. The sound signal may also be included modulated on a carrier with the video at such frequency spacing as to allow the use of conventional receivers with a simple adapter at the subscribers station. |
