Patent GB-1506924-A (GB)
Title: Cable television system
IPC: H04N7/173
Filed: 1975-04-18
Abstract: 1506924 Wired television PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 18 April 1975 [22 April 1974] 16078/75 Heading H4R In a cable television system, Fig. 1, a local programme centre 1 is connected via a multiple coaxial cable trunk 2 to a number of distribution stations 3 which receive VHF television signals which are divided between the cables of the trunk, each cable carrying a plurality of signals of different frequencies. A number of subscribers 4 are connected to each distribution station in star configuration by respective coaxial cables 5. At the distribution station, Fig. 2. a selecting apparatus, under the control of the subscriber, selects a desired programme for application to the subscribers cable, the selection being effected by changing the VHF signals from a plurality of the incoming coaxial cables to be frequency multiplexed in the UHF band, connecting the UHF band to a respective point for each subscriber by a signal splitter, and providing a UHF tuner T which, under the control of the subscriber, changes a selected one of the UHF television channels to a selected channel in the VHF band for application to the subscribers cable 5. As described the tuners T in the distribution station are controlled by the subscriber via a central control unit 10 (Fig. 1) in the local programme centre 1, and the subscriber is also provided with VHF radio and other television channels which are not selected by the tuner T. As shown the distribution station, Fig. 2, receives VHF signals on four cables P 1  to P 4 . The signals on cables P 1  and P 2  are amplified and fed to frequency changers C 1 , C 1 <SP>1</SP> to change the various programmes on the two cables from frequencies in the VHF band to different frequencies in the UHF band. The resulting signals are amplified, combined, and the combined UHF band applied via signal splitters S 1  S 2 , and amplifiers U 2  to tuners T, one for each subscriber, which are controlled by the control unit CU to translate a particular programme selected by the respective subscriber to a particular channel, e.g. channel 2, in the VHF band for application via low pass filters LP 1  and LP 2  to the subscribers cable 5. Other television signals and VHF radio signals are fed with their frequencies unchanged from the trunk cable P 3 , via amplifier V 5  and splitter S 3 , and mixed with the VHF channel 2 from the tuner for application to the subscribers lines. Further signals from trunk cable P 4  are changed via converters C 2  to positions in the UHF band and also applied to the subscribers cable. Using a conventional VHF/UHF receiver 6 the subscriber can then tune to the programme he has had selected for him on VHF channel 2 or any of the permanently available other VHF or UHF channels. A conventional FM receiver 7 can be used to receive the VHF radio transmission received from the subscribers cable. Selection of the programme that the subscriber wishes to have transmitted to him is effected in response to a coded interrogation signal transmitted to the subscriber at 114 MHz with the VHF signals on trunk cable P 3  which are transmitted unchanged via amplifier V 5 , splitter S 3  &c. The subscriber, in response to his specific interrogation code, transmits an answering signal at 30 MHz. Along with the subscribers programme selection the answering signal may also contain other information such as poll replies, intruder or fire alarms &c. The answer signal is returned through the distribution station via filter BP 5 , combiner 12 and return amplifier V 3 <SP>1</SP>, trunk cable P 3 , filter BP 3  in the local programme centre, and modulator/demodulator 11 to the control centre 10. Selection information is then routed from the control centre 10 through modulator demodulator 13, band pass filter BP 6 <SP>1</SP>, trunk cable P 1 , filter BP 7 <SP>1</SP>, and modem 14 to the control unit CU to effect appropriate control of the respective tuner T. Operation of the control unit CU is monitored over a return path via modem 14, BP 7 , amplifier V,', filter BP 6 , and modem 13. The control unit may store information for fee registration. Frequency band below 17 MHz which is free in the trunk and subscriber cable can be used for videophone connections, and the band from 17 to 22 MHz for the transmission of a video signal from the subscriber to the local programme centre. Facilities can be extended by provision of additional tuners at the distribution centre to provide selection programmes on two VHF channels, or by switching the HT between the tuners under control of the central station.