IL46827A - Wired broadcasting systems - Google Patents

Abstract

1480749 Wired broadcasting systems COMMUNICATIONS PATENTS Ltd 7 March 1975 [16 March 1974] 11791/74 Heading H4R In a wired broadcasting system a wide band coaxial cable 3 carries multichannel programme signals from a programme source 1 to a number of programme exchanges 4 to each of which a number of subscriber units 7 are connected. The channels in the wide band cable 3 are stacked one upon another in frequency, and each exchange has, for each subscriber a respective frequency translator 10 which is controlled from the respective subscriber unit 7 to convert a selected one of the stacked frequency signals to a predetermined other frequency which the subscriber is able to receive. As described the central station 1 transmits the programme signals on low deviation fm carriers, although standard UHF or VHF modulation can be used, and the cable 3 has a bandwidth of 600 MHz. Also applied to the cable are one or more pilot tones from generator 5. Each exchange can be connected to its subscribers by respective "Qwist" cables 8 of the type described in Specification 1,272,594 fed from the frequency translators 10 with a unit 11 to bypass the pilot signal around the translators 10 and apply it direct to the line. At the subscribers unit the pilot signal is utilized via frequency dividers or multipliers to generate selectively control signals which, fed back to the exchange, determine the parameters of the frequency translation so that the selected programme is returned to the subscriber over the respective one of lines 8 at the frequency which the subscriber can receive. In order to restrict reception of particular programmes the control unit 11 at the exchange may restrict the pilot tones applied to the subscribers line so that not all the programmes available can be selected by the subscriber to prevent subscribers receiving pay programmes &c. If desired the control unit 11 may be under the control of a central pay tv computer. In an alternative embodiment, Fig. 2 (not shown) the exchange 4 is linked to the subscribers units 7 via a single wide band cable (15) and individual subsidiary cables (16) and the various subscribers are allotted respective transmission frequencies, those near the exchange having frequencies higher than those more distant to increase the service area of the exchange. The subscriber will be provided with a frequency translator to change the frequency of the programme received from his line to that appropriate his receiver, the frequency translator utilizing the pilot tones received from the exchange and being located on or outside the subscribers premises. [GB1480749A]

Description

IMPROVEMENTS IN OR RELATING TO WIRED BROADCASTING SYSTEMS systems.

According to the present invention, there is provided a wired broadcasting system comprising a wideband coaxial cable for carrying multi-channel programme signals from a programme source or programme sources to a plurality of exchanges to each of which a plurality of subscriber units are connected, the programme source or sources being arranged to apply the signals to the cable stacked one upon the other in frequency, and each exchange comprising in respect of each subscriber a switchable frequency translator for selectively translating any one of the said stacked frequency signals to a predetermined other frequency which the subscriber unit is adapted to receive, switching means controllable from the respective subscriber unit to selectively switch the frequency translator, and an output circuit arranged to apply the said predetermined other frequency signal to a feeder cable to which the subscriber is connected.

Each of the subscribers may be connected to the respective exchange by a separate cable in which case the said other frequency may be exactly the same for each subscriber, or may be held in some other precise relationship to obtain optimum crossview protection on multi-pair twisted cables. This is a particularly advantageous arrangement for a system where HF amplitude modulated . , the subscribers may be connected to their respective exchange by a common cable , in which case the said other frequency is different for each subscriber.

The switching means located at the exchange may be controlled by tones from a selector unit at the subscriber unit. The selector unit may comprise harmonic and divider generators locked to a, master pilot tone or tones provided to the subscriber from the exchange.

If it is desired to prevent a subscriber from selecting a particular programme or programmes, means may be provided to prevent the or one or more of the master pilot tones reaching the subscriber, thereby disabling one or more of the harmonic and divider generators and making it impossible for the subscriber to provide the necessary selection tone or tones to select the programme or programmes.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings; in which: Fig.l schematically illustrates an embodiment of the invention in which a plurality of subscribers are linked to an exchange by separate respective cables and Fig. 2 schematically illustrates a further embodiment of the invention in which a plurality of subscribers are linked to an exchange by a common cable.

Referring to Fig. 1, a programme carrier signal generator 1 which comprises master frequency generators and F.M. modulators is provided with sound and vision programme signals on inputs 2. The signal generator 1 transmits programme signals on low deviation frequency modulated carriers stacked one upon the other in frequency to .a wide band coaxial cable 3. which is in turn connected, to a plurality of exchanges 4· only one of which is shown. Low deviation F.M. carriers are used as this reduced the problem of intermodulation distortion in frequency translators and permits adjacent channel selection after translation to a lower frequency band. Alternatively where the problem of intermodulation distortion may be reduced by controlled frequency band filtering the programme carrier signal generator may include standard VHF and UHF modulators. The cable may have a bandwidth of for example 600 MHz. A tone generator unit 5 controlled by an input 6 is located between the signal generator 1 and the cable 3 and arranged to provide to the cable 3 one or more master pilot tones.

Each exchange 4- is connected to a plurality of subscriber units 7 (only one of which is shown) by respective ones of a plurality of two or four wire "Qwist" cables;8 such as are described in our Patent Specification No. 1, 72,594- Each subscribers cable 8 is connected to a respective one of a series of baluns linked to a respective one of a series of frequency translators 10 arranged to translate the carrier frequencies to a frequency acceptable to the subscribers unit. A tone extractor and control unit 11 is arranged to extract the- master pilot tone or tones provided by the unit 5 and aply them to the baluns 9· Each subscriber unit comprises a receiver 12 adapted to receive the HP or M signals and a programme selector 13 which may comprise a bank of push buttons 1 , actuation of which provides one or more selection tones to the exchange along the respective cable 8. The selection tones or frequencies are generated by harmonic and divider generators locked to the master pilot tone or tones sent from the baluns 9 n the exchange along either of the pairs of wires in the cable 8.

When a subscriber wishes to receive a particular programme, he presses an appropriate push-button generating the required tone which identifies the frequency channel in the cable 3 on which, that programme is provided. The frequency translator and balun system of the subscriber is arranged so that, on receipt of any one tone or combination of tones, the frequency of the signal associated with that tone or tones is translated from the band occupied on the coaxial cable J to the low frequency band required by the subscribers unit 7· Where only one master tone is provided on the link 5 by the unit 5> the subscriber can be denied all"' the programmes on the line by preventing the master tone being transmitted to him from the exchange via tone extractor and control unit 11, the absence of the master tone disabling the selector 13» Where more than one master tone is provided, particular programmes or groups of programmes can be denied to a subscriber whilst other programmes or groups of programmes are supplied, by preventing the transmission of selected ones of the master tones from the exchange to..the subscriber., This selective denial facility may be useful in systems where for example payment for some but not all of the programmes is required, or where access to particular programmes has to be limited for security reasons.

Where the tones are associated with programmes for which additional payment is required the corresponding tone generator may be inhibited until the subscriber takes some action to indicate that he has paid or is prepared to accept payment for receiving the programme.' Alternatively selection of a pay programme may automatically indicate that payment is accepted. In one application all tone extractor and control units 11 may be under the control of a central pay TV computer and the computer may generate signals such as digital information over the link 5 or a secondary connection.

Referrin now to Pig. 2, an alternative arrangement is shown in which the individual cables 8 of Fig. 1 are replaced by a wide band coaxial cable 15 common to all of the subscribers connected to a particular exchange . Corresponding components of the Fig. 1 and Fig. 2 embodiments are given corresponding reference numerals.

Each subscriber is linked by a subsidiary coaxial cable 16 to the main cable 15} and is allocated a particular frequency band in the cables 15 and 16» Subscribers near to the exchange are allocated high frequency bands and subscribers remote from the exchange are allocated low frequency bands to obtain a maximum reach for exchanges at a given sending level.

The exchange is similar to that described with reference to Fig. 1 but includes in respect of each subscriber a characteristic frequency generator to provide selected programme signals on an F.M. carrier. VHF or UHF standard waveforms could alternatively be provided.

The subscriber unit is also similar to that described with reference to Fig. 1, but additionally includes a frequency translator for translating the characteristic^" carrier to a frequency acceptable to the subscribers receiver 12, and a characteristic selection tone generator 14, the exchange being arranged on receipt of the characteristic selection tone to allocate the frequency of a selected programme signal to a band dedicated to the particular subscriber. The local oscillators of the subscribers frequency translator may be controlled by pilot signals sent from the exchange to increase the security of the system. Alternatively or in addition this translator can be located outside the subscribers premises, for example on the pole route outside the premises, or at the end of the road in which the premises are located.

Alternative arrangements to those illustrated may of course be provided. For example, provision may be made for the variable tuning of exchange filters upon receipt of single or combination tone frequencies from the subscriber selector unit.

Claims (2)

1. 46*27- WHAT WE CLAIM IS: ^ 1. A wired broadcasting system comprising a wideband coaxial cable for carrying multi-channel programme signals from a programme source or programme sources to a plurality of exchanges to each of which a plurality of subscriber units are connected, the programme source or sources being arranged to apply the signals to the cable stacked one upon the other in frequency, and each exchange comprising in respect of each subscriber a sxLtchable frequency translator for selectively translating any one of the said stacked frequency signals to a predetermined other frequency which the subscriber unit is adapted to receive, switching means controllable from the respective subscriber unit to selectively switch the frequency translator, and an output circuit arranged to apply the said predetermined other frequency signal to a feeder cable to which the subscriber is connected.

2. A wired broadcasting system according to claim 1, wherein each of the subscribers is connected to the respective exchange by a separate cable. 5. A wired broadcasting system according to claim 2, wherein a single said other frequency is fed to each subscriber or a plurality of different frequencies having a precise relationship to each other are fed to respective ones of the subscribers. c A wired broadcasting system according to claim 1, wherein each of the subscribers is connected to the respective exchange by a common cable, the said other frequency being different for each of the subscribers connected to any one exchange. ~ ¾ " 5. A wired broadcasting system according to any precedi¾ -claim, comprising a selector unit at each subscriber unit for generating control tones to which the switching means located at the exchange is responsive. 6. A wired broadcasting system according to claim 5¾ comprising means for providing a master pilot tone or tones to the subscriber from the exchange, the selector unit comprising harmonic and divider generators locked to the master pilot tone or tones. 7. A wired broadcasting system according to claim 6, comprising means for preventing the or one or more of the master pilot tones from reaching a subscriber, thereby disabling the harmonic and divide generators. 8. A wired broadcasting system according to claim 7» wherein payment is required for receipt of one or more of the programme signals, comprising means for controlling the preventing means in dependence upon the making of a payment or indication of acceptance of a pay programme. 9. A wired broadcasting system according to claim 6, 7 or 8, comprising a tone generator unit arranged to provide one or more master pilot tones to the said wideband coaxial cable, and a tone extractor and control unit at each exchange arranged to extract and control the application of the master pilot tone or tones to each subscriber unit connected to the exchange. 10. A wired broadcasting system according to any preceding claim, comprising a programme carrier signal generator having -A- master frequency generators and "being arranged to receive sound and vision programme signal inputs and to transmit programme signals on the wideband coaxial cable. 11. A wired broadcasting system according to claim 10, wherein the programme carrier signal generator comprises FM modulators. 12. A wired broadcasting system according to claim 10. wherein the programme carrier signal generator comprises UHF or VHF modulators. 13 A wired broadcasting system according to any preceding claim, wherein the wideband coaxial cable has a bandwidth of 600 MHz. 14. A wired broadcasting system according to claim 4-or any claim appendant to claim 4-, wherein the common cable comprises a wideband coaxial cable to which each subscriber unit is connected by a respective subsidiary coaxial cable, subscribers near to the exchange being allocated high frequency bands and subscribers remote from the exchange being allocated low frequency bands. 15» A wired broadcasting system according to claim 4· or 1 , comprising at each exchange and in respect of each subscriber a characteristic frequency generator arranged to provide selected programme signals to the subscriber. 16. A wired broadcasting system according to claim 15, wherein the characteristic frequency generator provides selected programme signals on an FM carrier. 'ϊ 17- A wired broadcasting system according to claim 15 ^ wherein the characteristic frequency generator provides selected programme signals as standard UKF or VHP waveforms. 18. A wired broadcasting system according to claim 16, wherein each subscriber unit is provided with a frequency translator for translating the characteristic carrier to a frequency acceptable to the subscriber's receiver. 19. A wired broadcasting system according to claim 18, wherein the local oscillators of the subscribers frequency translator are controlled by pilot signals from the exchange. 20. A wired broadcasting system according to claim 18 or 19, wherein the subscribers frequency translator is located outside the subscribers premises. 21. A wired broadcasting system according to any one of claims 1 to 20, wherein each subscriber unit is provided with a characteristic selection tone generator, the exchange being arranged on receipt of the characteristic selection tone to allocate the frequency of a selected programme signal to a band dedicated to the particular subscriber. 22. A wired broadcasting system substantially as hereinbefore described with reference to Pig. 1 or Fig. 2 of the accompanying drawings.