| 摘要 |
1475363 Wired broadcasting systems COMMUNICATIONS PATENTS Ltd 2 Sept 1975 [21 Sept 1974 30 Oct 1974] 41195/74 and 47066/74 Heading H4R A selector, for use in a programme exchange of a wired broadcasting system comprises a plurality of semi-conductor switches 15-18 each of which operates a respective electromagnetic switch 11-14 to couple a subscribers line 5 to one of four programme sources 1-4 via switches 7-10, the programme source providing a holding current for the respective transistor via the respective operated switch. Depression of a reset button 23 at the subscriber station turns off transistors 22 and 15- 18. At the end of the reset pulse charged capacitor 25 switches on transistor 15 to couple the subscriber's line to programme wire 1, which may transmit a picture signal giving information as to the programmes of the other sources. The subscriber dials the number of the programme required, the programme number being equal to the designation of the programme source minus 1, and the transistor chain steps to leave only the corresponding transistor conducting. |
