| 摘要 |
<p>1306367 Wired television systems COMMUNICATIONS PATENTS Ltd 1 June 1970 [6 June 1969] 28870/69 Heading H4R In a wired broadcasting system, at least one subscriber is provided with means for originating programmes which are transmitted back to the central station over the lines on which the subscriber normally receives programmes, and the central station has means to make the subscriber originated programmes available to other subscribers of the system. As described the system is of the type of Specification 1,306,366 where programmes are distributed to the subscriber over lines 12 the programmes being selected in accordance with signals from the subscriber to the central station over a second pair of lines 12. The subscriber has a programme source, e.g. a TV camera 32 connected, via modulator 34 and filter 38, to a hybrid 25, which connects the receiver 30 and programme source to the lines 12. Programme transmission from the central station to the subscriber normally occupies the band 4-11 MHz while subscriber originated programmes are modulated to a band above 11 MHz and at the central station are fed, via a hybrid 16, to a modulator system which changes the signals to the 4-11 MHz band before applying them to a spare highway where . they can be selected, in the normal way by any of the subscribers. The programme originating subscriber receives his own signals via the central exchange to provide overall monitoring of the system. It is suggested that subscriber originated programmes may include data transmission or property surveillance which can take place on frequencies below 4 MHz and may go to a common monitoring station supervizing a number of subscribers and causing an alarm when the signal changes, e.g. on detection of an intruder or fire.</p> |
