GB1598970A

GB1598970A - Wired broadcasting systems

Info

Publication number: GB1598970A
Application number: GB2155278A
Authority: GB
Original assignee: Communications Patents Ltd
Current assignee: Communications Patents Ltd
Priority date: 1978-05-23
Filing date: 1978-05-23
Publication date: 1981-09-30
Also published as: FR2427022A1; JPS5510294A; DE2919223A1; NL7904024A

Description

(54) WIRED BROADCASTING SYSTEMS (71) We, COMMUNICATIONS PATENTS LIMITED, a British Company of Carlton House, Lower Regent Street, London, SW1Y 4 LS, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to wired broadcasting systems in which a number of television and other programmes may be transmitted through a distribution network to a plurality of subscribers, the subscribers being able to select desired programmes by controlling a switch.

Various systems have been proposed to make a number of television transmissions available to subscribers, and a system which offers a number of advantages over alternative systems is described in our British Patent Specification No. 1 272 594. This system is based on the use of programme exchanges each serving a group of subscribers each of whom has his own individual vision circuit to the programme exchange.

The vision circuit is provided by a twisted pair of conductors with intersticial conductors associated with each pair which are suitable for audio frequency circuits and/or for the transmission of signals for controlling switch means at the programme exchange. The switch means enable the selection of any one of a number of programmes by the subscriber for application to the twisted pair vision circuit for transmission to that subscriber. In general a number of such programme exchanges distributed over the network area each receives a number of colour transmissions through a trunk network from a central programme station, commonly referred to as the transmitter.

Such a system is extremely versatile and may be used not only for the transmission of vision signals from the programme exchanges to the individual subscribers, but a wide range of other facilities can be provided.

In many cases the subscriber will also be a telephone subscriber, and our British Patent Specification No. 1 414 127 describes how a telephone service to the subscriber may be provided by utilising the intersticial conductors of the wired broadcasting system. Specifically, Specification No. 1 414 127 describes and claims a wired broadcasting system in which each of a plurality of subscribers is connected to a programme exchange through the intermediary of a twisted pair of high frequency television signal conductors having associated therewith a pair of audio frequency conductors, each of the pair of audio frequency conductors being located in a corresponding one of a pair of interstices formed between the pair of high frequency television signal conductors, and in which means are provided whereby a telephone instrument at a subscribers premises may be connected to a telephone exchange through a signal path including that subscribers audio frequency signal conductors.

Our British Patent Application No.46864/76, Serial No. 1 589 914 which corresponds to German Patent Application No. P 27 48 661.9, describes solid state signalling devices which may be used in selection control switching arrangements in wired broadcasting systems, for example systems such as are described in Specification No. 1 414 127. Our British Patent Application No.46865/76, Serial No. 1 567 455, which corresponds to German Patent Application P 27 48 662.0, described solid state switches for effecting programme selections, which switches enable access to programmes on one or more particular channels of the system to be denied to subscribers under the control of the system operator.

The known programme denial arrangements enable the system operator to deny programmes to a particular subscribers receiver without regard to the identity of the person making the selection at the receiver. It is therefore not possible for a subscriber who should have access to normally denied programmes to override the programme denial arrangements. For example, it may be desired to restrict access to particular programmes to adults only. The only way this can be done with the known arrangements is to have one receiver to which only adults have access and from which all programmes are available, and a second receiver to which children have access and from which some programmes are not available.

It is an object of the present invention to provide a system in which programme denial arrangements can be overridden by selected subscribers to thereby enable better control over programme availability.

According to the present invention there is provided a wired broadcasting system comprising a central exchange at which programmes are made available, a plurality of subscriber units each connected to the exchange by a respective cable, programme selection switches in respect of each subscriber located at the exchange, means at each subscriber unit for applying programme selection control signals to the respective cable control the selection switches, means located at the exchange for selectively denying access by subscribers to programmes made available at the exchange, and means whereby at least one subscriber unit may override the programme denying means, characterised in that said programme denial override means comprises a transistor which when energised feeds a denial override current into the subscriber units respective cable, and means at the exchange for detecting the denial override current and overriding the programme denying means.

Preferably at least one subscriber unit comprises a lock switch which when actuated energises the transistor to feed the denial override current into the subscribers units respective cable.

The programme selection control signals and the denial override current may be applied to a common signal conductor in the cable, means being provided to slow the rise time of the denial override current to distinguish it from the selection control signals. A transistor responsive to the denial override current may be provided at the exchange, a capacitive/resistive circuit being connected to the transistor such that the transistor does not respond to short duration programme selection control signals.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a subscribers circuit for generating D.C. programme selection and reset pulses and denial override signals; Figure 2 shows a circuit for switching a single programme to a single subscriber; and Figure 3 shows circuitry for responding to a denial override signal.

Referring to Figure 1, a DIN plug connector shown schematically by dotted line 1 connects the illustrated circuit to one pair of a two-pair "Quist" cable such as is described in more detail in our British Patent Specification No.

1 272 594. The cable is not illustrated, but comprises one conductor pair of 26 s.w.g.

connected to carry any one selected HF television signal in the band 4 to 10MHz. The other conductor pair of the cable is of 27 s.w.g. and is connected to carry telephone signals and a plurality of F.M. radio signals on frequency dis- tinguished carriers in the band 14 to 22 MHz.

The cable links the subscriber to a central exchange at which programmes are made available. Further details of the general arrangement may be obtained by reference to our British Patent Specification No. 1 414 127.

The two H.F. television carrying conductors of the cable are connected to terminals 2, 3 of the DIN plug. Terminal 3 receives positive dial pulses and denial override signals, and also negative reset pulses.

When it is desired to select a programme, the subscriber presses appropriate ones of the buttons 4 to provide selection inputs to a button dialler integrated circuit chip 5 of the type used in button operated telephone handsets. The chip 5 is clocked by two-phase outputs of a clock generator 6 in known manner and as a result a series of dial pulses appears at the base of transistor 7. Each pulse turns transistor 7 on so that a negative going pulse is applied to the base of transistor 8 via capacitor 9. These negative going pulses turn on transistor 8 which applies positive going pulses to terminal 3 via normally closed switch contacts 10.

When it is desired to cancel a selected programme, a reset switch 11 is closed and transistor 12 turns on to apply a negative going pulse to terminal 3.

The pulses applied to terminal 3 are transmitted to a central exchange and the dial pulses are applied to a shift register which provides selection control signals to a series of switches, one in respect of each programme made available at the exchange. Similarly the reset pulse is applied to a reset control circuit which is adapted to open all the selector switches. The circuitry required is described in detail in our copending application No. 46864/76. Serial No.

1 589 914.

Referring now to Figure 2, a single switch is illustrated for applying a television signal appearing at input 13 to output 14. The output 14 is connected to a single subscribers cable. A switch control input is applied to terminal 15 in response to the selection by the subscriber of the programme appearing at input 13. A positive potential is normally applied to input 16.

The HF television signal applied to input 13 is passed to output 14 via series connected diode 17 and transistor 18 only so long as the potential at point 19 is such as to forward bias diode 17 and turn on transistor 18. The positive potential which is normally applied to input 16 is connected to point 19 by diode 20 and resistor 21.A transistor 22 controlled by input 15 is also connected to point 19.

In the "OFF" condition of the switch, the transistor 22 has a zero or negative potential applied to its base via input 15, thereby rendering it conductive so that the potential at point 19 falls towards ground, turning off transistor 18 and thereby isolating output 14 from input 13. When a positive potential smoothed by capacitor 23 is applied to the base of transistor 22, it is biased "OFF" allowing the potential at point 19 to rise to the positive level on input 16. The diode 17 is then forward biased and transistor 18 conductors. Thus the switch is in the "ON" condition and signals ap-,earinO ct input 13 are passed to output 14.

The output impedance of the transistor 22 is in shunt between the point 19 and ground. This arrangement improves the attenuation when transistor 22 conducts, i.e. when the switch is "OFF".

If it is decided that the subscriber connected to the illustrated switch is to be denied the programme applied to input 13, the positive potential is removed from input 16. Whatever the condition of input 15 thereafter, the diode 17 will not be forward biased, and thus the input 13 will be isolated from the output 14.

If it is desired to control access by the subscriber connected to the illustrated switch to the programme appearing at input 13, the positive potential is again removed from input 16 and in addition a positive potential is applied to input 24. The system operator can then allow access to the programme by closing a switch 25, or deny access to the programme by opening switch 25.

If it is desired to provide controlled access to the programme appearing at input 13, the switch 25 is closed and the input 24 is connected to the circuit of Figure 3.

Referring to Figure 3, a transistor 26 is normally nonconductive and terminal 24 is thus held at a negative potential. An input 27 is however connected to receive positive pulses applied to terminal 3 (Figure 1). Dial pulses thus appear at input 27 but are of insufficient duration to turn on the transistor 26 due to the provision of resistor 28 and capacitor 29.

Referring to Figure 1 ,the subscriber unit is provided with a key < ontrolled switch unit 30 comprising normally closed contacts 10 and normally open contacts 31. When a subscriber selects a programme to which access is controlled but not desired, the programme is initially not received as the input 24 (Figure 2) receives a negative potential. The subscriber who has in his possession a key may however actuate switch unit 30, thereby opening contacts 10 and closing contacts 31. As a result, transistor 32 (Figure 1) turns on releasing a positive DC denial override current into the subscribers cable via terminal 3. The rise time of this current is controlled by resistors 33,34 and capacitor 35 to be slow relative to the rise time of dial pulses so that a differentiating circuit responsive to dial pulses does not misinterpret the denial override current as a dial pulse.

The circuit of Figure 3 accepts the denial override current which appears at input 27 and the transistor 26 turns on. A positive tiozeiltIal applied to cermflinal 24 as a result enables the subscribsrs selection to be effective and the signal cot input 13 is applied to output 14. Thus a facility is provided for denying programmes to an operator of a subscriber unit unless the operator has a "denial override" key.

WHAT WE CLAIM IS: 1. A wired broadcasting system comprising a central exchange at which programmes are made available, a plurality of subscriber units each connected to the exchange by a respective cable, programme selection control signals to the respective cable to control the selection switches, means located at the exchange for selectively denying access by subscribers to programmes made available at the exchange, and means whereby at least one subscriber unit may override the programme denying means, characterised in that said programme denial override means comprises a transistor which when energised feeds a denial override current into the subscriber units respective cable, and means at the exchange for detecting the denial override current and overriding the programme denying means.

2. A wired broadcasting system according to Claim 1, wherein at least one subscriber unit comprises a lock switch which when actuated energises said transistor to feed the denial override current into the subscriber units respective cable.

3. A wired broadcasting system according to Claim 2, wherein said programme selection control signals and said denial override current are applied to a common signal conductor in said cable, means being provided to slow the rise time of said denial override current to distinguish the denial override current from said programme selection control signals.

4. A wired broadcasting system accordiing to Claim 3, comprising a further transistor responsive to said denial override current located at the exchange, and a capacitive and resistive circuit connected to the furthe transistor such that the further transistor does not respond to short duration programme selection control signals.

5. A wired broadcasting system substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the "ON" condition and signals ap-,earinO ct input 13 are passed to output 14. The output impedance of the transistor 22 is in shunt between the point 19 and ground. This arrangement improves the attenuation when transistor 22 conducts, i.e. when the switch is "OFF". If it is decided that the subscriber connected to the illustrated switch is to be denied the programme applied to input 13, the positive potential is removed from input 16. Whatever the condition of input 15 thereafter, the diode 17 will not be forward biased, and thus the input 13 will be isolated from the output 14. If it is desired to control access by the subscriber connected to the illustrated switch to the programme appearing at input 13, the positive potential is again removed from input 16 and in addition a positive potential is applied to input 24. The system operator can then allow access to the programme by closing a switch 25, or deny access to the programme by opening switch 25. If it is desired to provide controlled access to the programme appearing at input 13, the switch 25 is closed and the input 24 is connected to the circuit of Figure 3. Referring to Figure 3, a transistor 26 is normally nonconductive and terminal 24 is thus held at a negative potential. An input 27 is however connected to receive positive pulses applied to terminal 3 (Figure 1). Dial pulses thus appear at input 27 but are of insufficient duration to turn on the transistor 26 due to the provision of resistor 28 and capacitor 29. Referring to Figure 1 ,the subscriber unit is provided with a key < ontrolled switch unit 30 comprising normally closed contacts 10 and normally open contacts 31. When a subscriber selects a programme to which access is controlled but not desired, the programme is initially not received as the input 24 (Figure 2) receives a negative potential. The subscriber who has in his possession a key may however actuate switch unit 30, thereby opening contacts 10 and closing contacts 31. As a result, transistor 32 (Figure 1) turns on releasing a positive DC denial override current into the subscribers cable via terminal 3. The rise time of this current is controlled by resistors 33,34 and capacitor 35 to be slow relative to the rise time of dial pulses so that a differentiating circuit responsive to dial pulses does not misinterpret the denial override current as a dial pulse. The circuit of Figure 3 accepts the denial override current which appears at input 27 and the transistor 26 turns on. A positive tiozeiltIal applied to cermflinal 24 as a result enables the subscribsrs selection to be effective and the signal cot input 13 is applied to output 14. Thus a facility is provided for denying programmes to an operator of a subscriber unit unless the operator has a "denial override" key. WHAT WE CLAIM IS:

1. A wired broadcasting system comprising a central exchange at which programmes are made available, a plurality of subscriber units each connected to the exchange by a respective cable, programme selection control signals to the respective cable to control the selection switches, means located at the exchange for selectively denying access by subscribers to programmes made available at the exchange, and means whereby at least one subscriber unit may override the programme denying means, characterised in that said programme denial override means comprises a transistor which when energised feeds a denial override current into the subscriber units respective cable, and means at the exchange for detecting the denial override current and overriding the programme denying means.