CA1055597A - Cable television system - Google Patents
Cable television systemInfo
- Publication number
- CA1055597A CA1055597A CA224,652A CA224652A CA1055597A CA 1055597 A CA1055597 A CA 1055597A CA 224652 A CA224652 A CA 224652A CA 1055597 A CA1055597 A CA 1055597A
- Authority
- CA
- Canada
- Prior art keywords
- subscriber
- signals
- television
- trunk
- uhf
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
- H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
- H04N7/17345—Control of the passage of the selected programme
- H04N7/17354—Control of the passage of the selected programme in an intermediate station common to a plurality of user terminals
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
- H04N7/173—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal
- H04N2007/17372—Analogue secrecy systems; Analogue subscription systems with two-way working, e.g. subscriber sending a programme selection signal the upstream transmission being initiated or timed by a signal from upstream of the user terminal
Abstract
ABSTRACT:
Cable television systems having a multi-coax-tube VHF tree network between a program centre and a number of cable distribution stations and a star network between each cable distribution stations and the subscribers connected thereto. Signal selection in the cable distribution station is effected by conversion of the VHF signals to UHF signals, division of these signals into a plurality of output signals, and frequency selection and reconversion by means of a UHF
television turner for each subscriber.
Cable television systems having a multi-coax-tube VHF tree network between a program centre and a number of cable distribution stations and a star network between each cable distribution stations and the subscribers connected thereto. Signal selection in the cable distribution station is effected by conversion of the VHF signals to UHF signals, division of these signals into a plurality of output signals, and frequency selection and reconversion by means of a UHF
television turner for each subscriber.
Description
The invention relates to a cable television system in which a local program centre is connected via a multiple coax-tube trunk to a plurality of cable distribution stations which derive VHF television signals by branching from the trunk, which signals are divided between a plurality of coax-tubes of the trunk, each tube carrying a plurality of signals of different frequencies, in which system a plurality of subscribers are connected to each cable distribution station in a star-network configuration, with a coaxial subscriber's connection for each subscriber between the cable distribution station and the subscriber, whilst the cable distribution station contains selection apparatus which can be controlled from the subscribers' stations for selecting any one of the television signals supplied by the trunk and transmitting it to a subscriber's connection.
The conventional cable television systems have a tree structure in which from a main station first via one or more main lines but subsequently via an increasingly ramified branch system the signals are ultimately supplied to the subscribers. In such distribution systems the number of television programs which can be distributed is restricted owing to various circumstances.
When the complete UHF band is used a comparatively large number of signals can be transmitted, however, through very limited distances only, because at the higher UHF
frequencies the attenuation in the cables is very great. If larger distances are to be bridged, many interposed amplifiers
The conventional cable television systems have a tree structure in which from a main station first via one or more main lines but subsequently via an increasingly ramified branch system the signals are ultimately supplied to the subscribers. In such distribution systems the number of television programs which can be distributed is restricted owing to various circumstances.
When the complete UHF band is used a comparatively large number of signals can be transmitted, however, through very limited distances only, because at the higher UHF
frequencies the attenuation in the cables is very great. If larger distances are to be bridged, many interposed amplifiers
- 2 -are required, which renders the entire system expensive.
For this reason large-haul transport always is effected in the VHF band. Owing to the limited selectivity of the receivers a channel is frequently left unoccupied between every two occupied channels, although in the U.S.A. occupation of all channels is permitted to increase the capacity.
Another method of increasing the channel capacity in YHF systems is the use of what are generally referred to as S bands which lie between the standard television bands and are assigned to other services. This has the disadvantage that interference of television reception by these services and conversely occur, unless the entire system is provided with full high-frequency screening. In addition, the use of the S
bands requires the provision of special converters in the subscribers' homes, because conventional television receivers are not designed for reception of these bands.
A selection system as referred to hereinbefore and described~ for example, in the paper: "Two-way applications for cable television systems in the seventies", I.E.E.E.
Spectrum, November 1971, pages 53-54, "Discade system", in principle has an unlimited channel capacity. The star-configuration of the cable network between the cable distribution station and the subscribers moreover brings the use of two-way communication and of communication between any two subscribers within the range of the technically feasible.
In the aforementioned known selection television system the cable distribution station has a selector for each subscriber which connects the subscriber's connection of the relevant subscriber to one of the tubes (coaxial cables) of the multitube trunk. In order to keep the number of tubes in the trunk within reasonable limits, each coax-tube of the trunk carries two VHF television signals which both are transmitted to the subscriber's connection via the selector.
The apparatus provided in the subscriber's home then must have an additional selection facility (converter including an oscillator capable of being changed over) to enable a selection between the two signals.
The technical advantages of the known selection television system involve, however, high expenses attendant on its installation. It is an object of the present invention to provide a system which can be realised at considerably reduced cost, and for this purpose the cable television system according to the invention is characterized in that the selection apparatus is provided with conversion means for converting at least part of the VHF signals, which are divided between a plurality of coax-tubes and situated on a plurality of frequencies within each tube, into converted frequency division multiplex (FDM) UHF signals, with subsequent splitter means having an output for each subscriber connected thereto and with FDM UHF tuners which each are connected to a separate output of the splitter means, and are able by the relevant subscriber and the output signal of which after conversion to a standard television channel (for example VHF channel 2) is applied to the subscriber's connection of the relevant subscriber.
In the system according to the invention the controllable UHF tuner effectively selects both between television signals which are supplied through different coax-tubes of the trunk (space division multiplex) and between television signals which are supplied through one coax-tube of the trunk but at different frequencies (frequency division multiplex). As a result, the equipment in the subscriber's home is simplified and moreover the same number of television programs can be supplied by a trunk comprising a smaller number of coax-tubes. Furthermore the invention provides a substantial saving in that in the cable distribution station channel selectors are used which select a signal from a plurality of signals at adjacent frequencies (frequency division multiplex selectors) instead of the selectors which are used in known selection television systems and which select a connection from a plurality of connections (space division multiplex selectors), for the former type of selectors is cheaply available owing to recent developments in television receiver technology.
Because in a selection television system of the type proposed only a comparatively narrow frequency band of the subscriber's connection is required, the system can simply be extended by a system on the basis of general distribution.
In this case the cable television system according to the invention is characterized in that part of the VHF television signals and/or VHF frequency-modulation radio signals either directly or after conversion, for example to the UHF band, are applied to all the subscribers' connections.
In a selection television system each selector in the cable distribution station must be remotely controlled by the relevant subscriber. According to a further aspect of the invention the UHF tuners in the cable distribution stations are not directly controlled by the subscribers but indirectly by a computer in the local program centre via a first commun-ication channel, using a known interrogating system by means of which the local program centre collects the selection in-formation from the subscribers via a second communication channel. This permits further simplification of the equipment to be installed at the subscribers' ends.
The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which Fig. 1 shows schematically a local program centre and the cabling configuration which may be used in a cable television system according to the invention, Fig. 2 shows schematically a cable distribution station and a subscriber's station which may be used in a television distribution system according to the invention, and Fig. 3 shows the frequency positions of the sig-nals transmitted through the subscriber's connection.
Referring now to Fig. 1, a local program centre 1, which includes at least one program source, for example a first program source 16 for standard television signals, a second program source 17 for local television signals, a third program source 18 for selection television signals and a fourth program source 19 for still videotheque pictures, transmits these television signals via a multiple coax-tube trunk 2 to a plurality of cable distribution stations 3. The trunks in actual fact form a tree network, the same informat-ion being supplied to all the cable distribution stations.
Signal transmission via the trunk is effected in 1.055597 the VHF bands and may, for example, take place at standard frequencies, one channel being left unoccupied between each two occupied channels. In this case, at a maximum 6 television signals can be transmitted in each coax-tube and the overall capacity of a trunk comprising, say, 4 coax-tubes is 24 television signals. If the capacity is to be increased without using more coax-tubes in the trunk, there is no serious ob-jection to the use of non-standard television frequencies ~for example in the S-band of 118 to 174 MHz situated below the band III). Transmission via the trunk is restricted to the VHF frequencies and any further extension of the capacity of the trunk is to be found in the use of more coax-tubes in the trunk in order to maintain attenuation in the trunk at a sufficiently low value so that in general the trunk amplifiers required in the trunk can be incorporated in the cable dis-tribution stations and hence only in exceptional cases where two cable distribution stations are a large distance apart additional amplifiers between these stations are required.
To each cable distribution station a number of (for example about 300) subscribers are connected, each sub-scriber being connected to a cable distribution station via a separate coaxial subscriber's connection 5 (star config-uration).
In the cable distribution station of Fig. 2 each coax-tube Pl, P2, P3, P4 of the incoming trunk 2 is connected to the input of a VHF amplifier Vl, V2, V3, V4 respectively, The outputs of the amplifiers feed coax-tubes Ql, Q2, Q3, Q4, respectively of the outgoing trunk which supplies further cable distribution stations. Consequently the amplifiers Vl to V4 act as trunk amplifiers.
~055597 A small part of the output signal power of the trunk amplifier Vl is supplied to the inputs of VHF/UHF chan-nel converters Cl. Each of these converters converts one of the VHF channels supplied via the coaxial pipe Pl to a given UHF channel in a manner such, however, that the resulting UHF
channels are arranged in regular sequence, every two occupied channels being separated by an unoccupied intermediate chan-nel. Similarly a small part of the output signal power of the trunk amplifier V2 is supplied to the inputs of further VHF/UHV
channel converters Cl' which convert the VHF signals from the coax pipe P2 to the UHF band. The output signals of the con-verters Cl and Cl' are amplified by UHF channel amplifiers Ul and Ul' respectively, brought to substantially equal levels and then combined and applied to the input of a splitter net-work Sl. If, for example, six television signals are supplied in VHF channels 2, 4, 5, 7, 9 and 11 through the coaxial pipe Pl and if another six television signals in the same VHF chan-nels are supplied through the coaxial pipe P2, these 12 tele-vision signals can all appear at the input of the splitter Sl side by side in the UHF band, for example in odd-numbered UHF
channels 21, 23, ..., 43.
The incoming VHF signals which are divided between a plurality of coax-tubes (space division multiplex) and also between a plurality of frequencies (frequency division multi-plex) thus all are converted to frequency division multiplex in the UHF band.
The UHF signal energy is divided by the splitter Sl between a plurality of outputs, amplified in wide-band UHF
amplifiers U2, divided again by splitters S2 and then supplied to UHF television tuners T. As a result, all the UHF signals produced in the converters Cl and Cl' are available at the input of each tuner T. For each subscriber equipped with means for receiving selection television signals at least one tuner T is provided which at the command of the relevant subscriber is tuned by a control unit CU. The tuners T may be conventional UHF tuners which are generally used in television receivers and are inexpensive in manufacture. When using a varactor tuner the control unit CU supplies the desired tuning voltage for the varactors of each tuner. The tuner T selects from all the UHF signals applied via the splitter S2 that UHF signal which is set by the control unit CU and is desired by the relevant subscriber and converts it to a standard television channel, for example the VHF channel 2 (47 to 53 MHz). This signal is applied to the coaxial subscriber's connection of the relevant subscriber via a first low-pass filter LPl and a second low-pass filter LP2. Thus the selection television channel sup-plied via the coaxial pipes Pl and P2 are always converted to the channel 2. This channel is particularly suited for further transport of the selected television signal to the subscriber, because it is substantially not used by broadcast television transmitters. Owing to the imperfections in radiation-tight-ness of the cable 5 and of the apparatus in the subscriber's station, transport through another channel may suffer from in-terference by signals which are on the air in the same channel.
If a subscriber wants to be able to receive two selection television signals simultaneously, for example for two receivers, this wish can simply be fulfilled by assigning two tuners to him, adjusting the output frequency of one tuner to channel 2 and that of the other tuner to, for example, channel 4, and connecting the outputs of both tuners to the same low-pass filter LPl.
In addition to the aforedescribed selection tele-vision system using signals supplied via Pl and P2, the de-vice of Fig. 2 has facilities for supplying television signals to all subscribers in accordance with conventional television distribution systems. For this purpose VHF signals supplied via the coaxial pipe P3 and amplified in the amplifier V3, which signals all lie in band III (174 to 230 MHz), are ap-plied via a further VHF amplifier V5 to a splitter S3 having one output for each subscriber. The output signal of this splitter is also applied via a high-pass filter HPl, which passes the VHF band III, to the input of the low-pass filter LP2 which passes the YHF bands I and III. Thus the television signals from the coaxial pipe P3 are continuously, and without conversion, supplied to all subscribers. Through the pipe P3 the frequency-modulation radio signals of the band II also can be supplied to all subscribers.
The VHF television signals from the coaxial pipe P4 are amplified in the YHF amplifier V4 and then supplied to six VHF-UHF converters C2 by which each of the VHF channels of the pipe P4 is converted to a UHF channel, for example to one of the low UHF channels 21, 23, 25, 27, 29, 31. After amp-lification in UHF channel amplifiers U3 these signals are added together. The resulting UHF television band is divided in a UHF splitter S4, amplified in UHF-band amplifiers U4, divided again in second UHF splitters S5, again amplified in UHF-band amplifiers U5 for part of the subscribers, and then via a high-pass filter HP2 which passes the UHF band supplied to the subscriber's connection 5.
Fig. 3 is an illustrative diagram showing the fre-quency positions of the signals in the subscriber's connection 5. The total frequency band consists of a distribution band above 40 MHz comprising signals transmitted to the subscriber and of a return band comprising signals from the subscriber.
The UHF band IV (channels 21 to 31) accommodates 6 television signals supplied via P4 to all subscribers.
The VHF band III (channels 5 to 11) accommodates 4 television signals which are supplied through P3 and are directly, without conversion, transmitted to all subscribers.
The frequency-modulation radio band II supplied through P3 is also directly transmitted to all subscribers.
The VHF band I (channels 2 and 4) accommodates one or two television signals which a subscriber has selected from the plurality of television signals which are supplied via the coaxial pipes Pl and P2.
It should be mentioned that the cable television system described makes it possible that part of the subscribers can receive only normal television distribution of the sig-nals supplied via P3 and P4 if they do not want the selection television facility with regard to the signals from the coaxial pipes Pl and P2.
In the subscriber's station the subscriber con-nection 5 is connected to a conventional television receiver 6 having VHF/UHF tuning capabilities and, via a band-pass filter BPl for the band II, to a frequency-modulation radio receiver 7. Via band-pass filters BP2 and BP2' and a mod-ulation-demodulation device 8 the subscriber's connection 5 is also connected to a control device 9.
Control of the entire system preferably is ef-fected by means of digital techniques, binary interrogating signals being transmitted from a central control unit 10 (Fig. 1) in the local program centre sequentially for each subscriber via an interrogating communication channel D' (Fig. 3) which may lie in an unused frequency band of the S channels, for example in the band of 112 to 116 MHz. For this purpose interrogating signals from the cont~ol unit 10 modulate a carrier of 114 MHz in a modulation-demodulation device 11 and then are applied via a band-pass filter BP3' to the coax-tube (P3) of the trunk 2 which ensures VHF trans-mission to the subscriber. Thus, in the cable distribution station the interrogating communication channel comprises V3, V5, S3, HPl and LP2. ln the subscriber's station the interrogating signals pass through the band-pass filter BP2, then are demodulated in the device 8 and subsequently reach the control device 9. The interrogating signals from the cen-tral control unit 10 include an address code which is specific for each subscriber. When the control unit 9 receives an in-terrogating signal containing the address code which is specific to this control unit, it returns a reply code which includes in-formation inserted by the subscriber into a store of the control device. This store may be filled with selection television in-formation, but also with other subscriber replies, such as re-plies to polls held via television, intruder or fire alarms, etc.
In the device 8 the reply signal modulates a carrier of 30 MHz.
This signal (D) which lies in the return band returns to the central control unit 10 via BP2', a band-pass filter BP5, a matching network 12, a return band amplifier V3' connected in shunt across V3, BP3 and the device 11. When using a bit frequency of 1 Megabit/s, interrogation of a subscriber and the subsequent reply for the subscriber need take no more than 0.2 ms so that 5,000 subscribers can be interrogated per second.
The information collected by the central control unit 10 in this manner is primarily used to set the control unit CU of the cable distribution station and hence the tun-ing of the tuners T via a control channel in the.unused fre-quency-modulation band of the coax-tube Pl via a 100 Mhz modulator-demodulator 13, a band-pass filter BP6', the coax-tube Pl of the trunk 2, a band-pass filter BP7' and a modu-lator-demodulator 14. By means of a channel reserved for this purpose and situated in the return band (for example at 26 MHz) the resulting setting of the control unit is checked.
The return path then comprises the modulator-demodulator 14, a band-pass filter BP7, a return amplifier Vl' connected in parallel across Vl, the coax-tube Pl, a band-pass filter BP6 and the device 13.
The information in the central control unit 10 is further stored in a central store 15 for fee registration.
Finally the central unit 10 controls one or more of the program sources of the local program centre in order to transmit a given television signal at the demand of a sub-scriber.
It should be mentioned that the capacity of the selection television system shown can be expanded by increas-ing the number of coax-tubes in the trunk. However, the cap-acity of the system is limited by the number of television signals which can be applied to the tuner T. When using UHF
tuners capable of handling adjacent signals without mutual interference the capacity can be expanded to about 48 tele-vision channels. By using a continuous UHF/VHF tuner as the tuner T, i.e. a tuner capable of handling also the VHF bands I and III and the intermediate channels, further capacity increase is possible. In addition, or instead, the incoming signals can be divided into two groups and each subscriber may be provided with two tuners, one for selection from the second group of signals. Selection between the two groups then is effected by switching the tuners from the control unit CU, for example by switching their supply voltages on and off.
The frequency space from 17 to 22 MHz which still is free in the return band both in the trunk and in the sub-scriber's connection can be used in a non-detailed manner to a limited extent for transmitting a television signal gen-erated in the subscriber's station, (for example for ad-vertising purposes) to the cable distribution station and from there via one of the coax-tubes of the trunk to the local program centre, by which it can be distributed to one or more other subscribers.
The frequency space below 17 MHz which still is free may be used for a videophone connection, for example the space from 6 to 8 MHz for transmission to the subscriber and the space from 10 to 12 MHz for transmission from the subscriber.
In general, the telephone network is preferably isolated entirely from the television distribution network.
However, during construction, considerable savings are ob-tainable by localising the cable distribution stations of both networks at the same location and by using the same cable ducts for both networks.
For this reason large-haul transport always is effected in the VHF band. Owing to the limited selectivity of the receivers a channel is frequently left unoccupied between every two occupied channels, although in the U.S.A. occupation of all channels is permitted to increase the capacity.
Another method of increasing the channel capacity in YHF systems is the use of what are generally referred to as S bands which lie between the standard television bands and are assigned to other services. This has the disadvantage that interference of television reception by these services and conversely occur, unless the entire system is provided with full high-frequency screening. In addition, the use of the S
bands requires the provision of special converters in the subscribers' homes, because conventional television receivers are not designed for reception of these bands.
A selection system as referred to hereinbefore and described~ for example, in the paper: "Two-way applications for cable television systems in the seventies", I.E.E.E.
Spectrum, November 1971, pages 53-54, "Discade system", in principle has an unlimited channel capacity. The star-configuration of the cable network between the cable distribution station and the subscribers moreover brings the use of two-way communication and of communication between any two subscribers within the range of the technically feasible.
In the aforementioned known selection television system the cable distribution station has a selector for each subscriber which connects the subscriber's connection of the relevant subscriber to one of the tubes (coaxial cables) of the multitube trunk. In order to keep the number of tubes in the trunk within reasonable limits, each coax-tube of the trunk carries two VHF television signals which both are transmitted to the subscriber's connection via the selector.
The apparatus provided in the subscriber's home then must have an additional selection facility (converter including an oscillator capable of being changed over) to enable a selection between the two signals.
The technical advantages of the known selection television system involve, however, high expenses attendant on its installation. It is an object of the present invention to provide a system which can be realised at considerably reduced cost, and for this purpose the cable television system according to the invention is characterized in that the selection apparatus is provided with conversion means for converting at least part of the VHF signals, which are divided between a plurality of coax-tubes and situated on a plurality of frequencies within each tube, into converted frequency division multiplex (FDM) UHF signals, with subsequent splitter means having an output for each subscriber connected thereto and with FDM UHF tuners which each are connected to a separate output of the splitter means, and are able by the relevant subscriber and the output signal of which after conversion to a standard television channel (for example VHF channel 2) is applied to the subscriber's connection of the relevant subscriber.
In the system according to the invention the controllable UHF tuner effectively selects both between television signals which are supplied through different coax-tubes of the trunk (space division multiplex) and between television signals which are supplied through one coax-tube of the trunk but at different frequencies (frequency division multiplex). As a result, the equipment in the subscriber's home is simplified and moreover the same number of television programs can be supplied by a trunk comprising a smaller number of coax-tubes. Furthermore the invention provides a substantial saving in that in the cable distribution station channel selectors are used which select a signal from a plurality of signals at adjacent frequencies (frequency division multiplex selectors) instead of the selectors which are used in known selection television systems and which select a connection from a plurality of connections (space division multiplex selectors), for the former type of selectors is cheaply available owing to recent developments in television receiver technology.
Because in a selection television system of the type proposed only a comparatively narrow frequency band of the subscriber's connection is required, the system can simply be extended by a system on the basis of general distribution.
In this case the cable television system according to the invention is characterized in that part of the VHF television signals and/or VHF frequency-modulation radio signals either directly or after conversion, for example to the UHF band, are applied to all the subscribers' connections.
In a selection television system each selector in the cable distribution station must be remotely controlled by the relevant subscriber. According to a further aspect of the invention the UHF tuners in the cable distribution stations are not directly controlled by the subscribers but indirectly by a computer in the local program centre via a first commun-ication channel, using a known interrogating system by means of which the local program centre collects the selection in-formation from the subscribers via a second communication channel. This permits further simplification of the equipment to be installed at the subscribers' ends.
The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which Fig. 1 shows schematically a local program centre and the cabling configuration which may be used in a cable television system according to the invention, Fig. 2 shows schematically a cable distribution station and a subscriber's station which may be used in a television distribution system according to the invention, and Fig. 3 shows the frequency positions of the sig-nals transmitted through the subscriber's connection.
Referring now to Fig. 1, a local program centre 1, which includes at least one program source, for example a first program source 16 for standard television signals, a second program source 17 for local television signals, a third program source 18 for selection television signals and a fourth program source 19 for still videotheque pictures, transmits these television signals via a multiple coax-tube trunk 2 to a plurality of cable distribution stations 3. The trunks in actual fact form a tree network, the same informat-ion being supplied to all the cable distribution stations.
Signal transmission via the trunk is effected in 1.055597 the VHF bands and may, for example, take place at standard frequencies, one channel being left unoccupied between each two occupied channels. In this case, at a maximum 6 television signals can be transmitted in each coax-tube and the overall capacity of a trunk comprising, say, 4 coax-tubes is 24 television signals. If the capacity is to be increased without using more coax-tubes in the trunk, there is no serious ob-jection to the use of non-standard television frequencies ~for example in the S-band of 118 to 174 MHz situated below the band III). Transmission via the trunk is restricted to the VHF frequencies and any further extension of the capacity of the trunk is to be found in the use of more coax-tubes in the trunk in order to maintain attenuation in the trunk at a sufficiently low value so that in general the trunk amplifiers required in the trunk can be incorporated in the cable dis-tribution stations and hence only in exceptional cases where two cable distribution stations are a large distance apart additional amplifiers between these stations are required.
To each cable distribution station a number of (for example about 300) subscribers are connected, each sub-scriber being connected to a cable distribution station via a separate coaxial subscriber's connection 5 (star config-uration).
In the cable distribution station of Fig. 2 each coax-tube Pl, P2, P3, P4 of the incoming trunk 2 is connected to the input of a VHF amplifier Vl, V2, V3, V4 respectively, The outputs of the amplifiers feed coax-tubes Ql, Q2, Q3, Q4, respectively of the outgoing trunk which supplies further cable distribution stations. Consequently the amplifiers Vl to V4 act as trunk amplifiers.
~055597 A small part of the output signal power of the trunk amplifier Vl is supplied to the inputs of VHF/UHF chan-nel converters Cl. Each of these converters converts one of the VHF channels supplied via the coaxial pipe Pl to a given UHF channel in a manner such, however, that the resulting UHF
channels are arranged in regular sequence, every two occupied channels being separated by an unoccupied intermediate chan-nel. Similarly a small part of the output signal power of the trunk amplifier V2 is supplied to the inputs of further VHF/UHV
channel converters Cl' which convert the VHF signals from the coax pipe P2 to the UHF band. The output signals of the con-verters Cl and Cl' are amplified by UHF channel amplifiers Ul and Ul' respectively, brought to substantially equal levels and then combined and applied to the input of a splitter net-work Sl. If, for example, six television signals are supplied in VHF channels 2, 4, 5, 7, 9 and 11 through the coaxial pipe Pl and if another six television signals in the same VHF chan-nels are supplied through the coaxial pipe P2, these 12 tele-vision signals can all appear at the input of the splitter Sl side by side in the UHF band, for example in odd-numbered UHF
channels 21, 23, ..., 43.
The incoming VHF signals which are divided between a plurality of coax-tubes (space division multiplex) and also between a plurality of frequencies (frequency division multi-plex) thus all are converted to frequency division multiplex in the UHF band.
The UHF signal energy is divided by the splitter Sl between a plurality of outputs, amplified in wide-band UHF
amplifiers U2, divided again by splitters S2 and then supplied to UHF television tuners T. As a result, all the UHF signals produced in the converters Cl and Cl' are available at the input of each tuner T. For each subscriber equipped with means for receiving selection television signals at least one tuner T is provided which at the command of the relevant subscriber is tuned by a control unit CU. The tuners T may be conventional UHF tuners which are generally used in television receivers and are inexpensive in manufacture. When using a varactor tuner the control unit CU supplies the desired tuning voltage for the varactors of each tuner. The tuner T selects from all the UHF signals applied via the splitter S2 that UHF signal which is set by the control unit CU and is desired by the relevant subscriber and converts it to a standard television channel, for example the VHF channel 2 (47 to 53 MHz). This signal is applied to the coaxial subscriber's connection of the relevant subscriber via a first low-pass filter LPl and a second low-pass filter LP2. Thus the selection television channel sup-plied via the coaxial pipes Pl and P2 are always converted to the channel 2. This channel is particularly suited for further transport of the selected television signal to the subscriber, because it is substantially not used by broadcast television transmitters. Owing to the imperfections in radiation-tight-ness of the cable 5 and of the apparatus in the subscriber's station, transport through another channel may suffer from in-terference by signals which are on the air in the same channel.
If a subscriber wants to be able to receive two selection television signals simultaneously, for example for two receivers, this wish can simply be fulfilled by assigning two tuners to him, adjusting the output frequency of one tuner to channel 2 and that of the other tuner to, for example, channel 4, and connecting the outputs of both tuners to the same low-pass filter LPl.
In addition to the aforedescribed selection tele-vision system using signals supplied via Pl and P2, the de-vice of Fig. 2 has facilities for supplying television signals to all subscribers in accordance with conventional television distribution systems. For this purpose VHF signals supplied via the coaxial pipe P3 and amplified in the amplifier V3, which signals all lie in band III (174 to 230 MHz), are ap-plied via a further VHF amplifier V5 to a splitter S3 having one output for each subscriber. The output signal of this splitter is also applied via a high-pass filter HPl, which passes the VHF band III, to the input of the low-pass filter LP2 which passes the YHF bands I and III. Thus the television signals from the coaxial pipe P3 are continuously, and without conversion, supplied to all subscribers. Through the pipe P3 the frequency-modulation radio signals of the band II also can be supplied to all subscribers.
The VHF television signals from the coaxial pipe P4 are amplified in the YHF amplifier V4 and then supplied to six VHF-UHF converters C2 by which each of the VHF channels of the pipe P4 is converted to a UHF channel, for example to one of the low UHF channels 21, 23, 25, 27, 29, 31. After amp-lification in UHF channel amplifiers U3 these signals are added together. The resulting UHF television band is divided in a UHF splitter S4, amplified in UHF-band amplifiers U4, divided again in second UHF splitters S5, again amplified in UHF-band amplifiers U5 for part of the subscribers, and then via a high-pass filter HP2 which passes the UHF band supplied to the subscriber's connection 5.
Fig. 3 is an illustrative diagram showing the fre-quency positions of the signals in the subscriber's connection 5. The total frequency band consists of a distribution band above 40 MHz comprising signals transmitted to the subscriber and of a return band comprising signals from the subscriber.
The UHF band IV (channels 21 to 31) accommodates 6 television signals supplied via P4 to all subscribers.
The VHF band III (channels 5 to 11) accommodates 4 television signals which are supplied through P3 and are directly, without conversion, transmitted to all subscribers.
The frequency-modulation radio band II supplied through P3 is also directly transmitted to all subscribers.
The VHF band I (channels 2 and 4) accommodates one or two television signals which a subscriber has selected from the plurality of television signals which are supplied via the coaxial pipes Pl and P2.
It should be mentioned that the cable television system described makes it possible that part of the subscribers can receive only normal television distribution of the sig-nals supplied via P3 and P4 if they do not want the selection television facility with regard to the signals from the coaxial pipes Pl and P2.
In the subscriber's station the subscriber con-nection 5 is connected to a conventional television receiver 6 having VHF/UHF tuning capabilities and, via a band-pass filter BPl for the band II, to a frequency-modulation radio receiver 7. Via band-pass filters BP2 and BP2' and a mod-ulation-demodulation device 8 the subscriber's connection 5 is also connected to a control device 9.
Control of the entire system preferably is ef-fected by means of digital techniques, binary interrogating signals being transmitted from a central control unit 10 (Fig. 1) in the local program centre sequentially for each subscriber via an interrogating communication channel D' (Fig. 3) which may lie in an unused frequency band of the S channels, for example in the band of 112 to 116 MHz. For this purpose interrogating signals from the cont~ol unit 10 modulate a carrier of 114 MHz in a modulation-demodulation device 11 and then are applied via a band-pass filter BP3' to the coax-tube (P3) of the trunk 2 which ensures VHF trans-mission to the subscriber. Thus, in the cable distribution station the interrogating communication channel comprises V3, V5, S3, HPl and LP2. ln the subscriber's station the interrogating signals pass through the band-pass filter BP2, then are demodulated in the device 8 and subsequently reach the control device 9. The interrogating signals from the cen-tral control unit 10 include an address code which is specific for each subscriber. When the control unit 9 receives an in-terrogating signal containing the address code which is specific to this control unit, it returns a reply code which includes in-formation inserted by the subscriber into a store of the control device. This store may be filled with selection television in-formation, but also with other subscriber replies, such as re-plies to polls held via television, intruder or fire alarms, etc.
In the device 8 the reply signal modulates a carrier of 30 MHz.
This signal (D) which lies in the return band returns to the central control unit 10 via BP2', a band-pass filter BP5, a matching network 12, a return band amplifier V3' connected in shunt across V3, BP3 and the device 11. When using a bit frequency of 1 Megabit/s, interrogation of a subscriber and the subsequent reply for the subscriber need take no more than 0.2 ms so that 5,000 subscribers can be interrogated per second.
The information collected by the central control unit 10 in this manner is primarily used to set the control unit CU of the cable distribution station and hence the tun-ing of the tuners T via a control channel in the.unused fre-quency-modulation band of the coax-tube Pl via a 100 Mhz modulator-demodulator 13, a band-pass filter BP6', the coax-tube Pl of the trunk 2, a band-pass filter BP7' and a modu-lator-demodulator 14. By means of a channel reserved for this purpose and situated in the return band (for example at 26 MHz) the resulting setting of the control unit is checked.
The return path then comprises the modulator-demodulator 14, a band-pass filter BP7, a return amplifier Vl' connected in parallel across Vl, the coax-tube Pl, a band-pass filter BP6 and the device 13.
The information in the central control unit 10 is further stored in a central store 15 for fee registration.
Finally the central unit 10 controls one or more of the program sources of the local program centre in order to transmit a given television signal at the demand of a sub-scriber.
It should be mentioned that the capacity of the selection television system shown can be expanded by increas-ing the number of coax-tubes in the trunk. However, the cap-acity of the system is limited by the number of television signals which can be applied to the tuner T. When using UHF
tuners capable of handling adjacent signals without mutual interference the capacity can be expanded to about 48 tele-vision channels. By using a continuous UHF/VHF tuner as the tuner T, i.e. a tuner capable of handling also the VHF bands I and III and the intermediate channels, further capacity increase is possible. In addition, or instead, the incoming signals can be divided into two groups and each subscriber may be provided with two tuners, one for selection from the second group of signals. Selection between the two groups then is effected by switching the tuners from the control unit CU, for example by switching their supply voltages on and off.
The frequency space from 17 to 22 MHz which still is free in the return band both in the trunk and in the sub-scriber's connection can be used in a non-detailed manner to a limited extent for transmitting a television signal gen-erated in the subscriber's station, (for example for ad-vertising purposes) to the cable distribution station and from there via one of the coax-tubes of the trunk to the local program centre, by which it can be distributed to one or more other subscribers.
The frequency space below 17 MHz which still is free may be used for a videophone connection, for example the space from 6 to 8 MHz for transmission to the subscriber and the space from 10 to 12 MHz for transmission from the subscriber.
In general, the telephone network is preferably isolated entirely from the television distribution network.
However, during construction, considerable savings are ob-tainable by localising the cable distribution stations of both networks at the same location and by using the same cable ducts for both networks.
Claims (4)
1. Cable television system in which a local program centre is connected via a multiple coax-tube trunk to a plurality of cable distribution stations which, by branching of the trunk receive VHF television signals which are divided between a plurality of coax-tubes of the trunk each tube carrying a plurality of signals of different frequencies, a plurality of subscribers being connected to each cable distribution station in a star-oonfiguration with a coaxial subscriber's connection between the cable distribution station and each subscriber, whilst the cable distribution station contains selection apparatus which can be controlled from the subscriber's stations for selecting any one of the television signals supplied by the trunk and transmitting it to a subscriber's connection, characterized in that the selection apparatus is provided with conversion means for converting at least part of the UHF signals which are divided between a plurality of coax-tubes and situated on a plurality of frequencies within each tube into converted (frequency division multiplex FDM)-UHF signals, with subsequent splitter means having an output for each subscriber connected thereto and with FDM-UHF tuners which each are connected to a separate output of the splitter means and are controllable by the relevant subscriber and the output signal of which after conversion to a standard television channel (for example the VHF channel 2) is applied to the subscriber's connection of the relevant subscriber.
2. Cable television system as claimed in Claim 1, characterized in that part of the VHF television signals and/or VHF frequency-modulation radio signals supplied via the trunk are applied to all the subscribers' connections without conversion.
3. Cable television system as claimed in Claim 1, characterized in that part of the VHF television signals supplied via the trunk are applied, after conversion, for example in the UHF band, to all the subscribers' connections.
4. Cable television system as claimed in Claim 1, characterized in that the control of the FDM-UHF tuners in the cable distribution stations is effected from the local program centre via a first communication channel, using a known interrogating system by means of which the local program centre collects the selection information from the subscribers via a second communication channel.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7405405A NL7405405A (en) | 1974-04-22 | 1974-04-22 | TELEVISION DISTRIBUTION SYSTEM. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1055597A true CA1055597A (en) | 1979-05-29 |
Family
ID=19821200
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA224,652A Expired CA1055597A (en) | 1974-04-22 | 1975-04-15 | Cable television system |
Country Status (13)
| Country | Link |
|---|---|
| JP (1) | JPS604633B2 (en) |
| AT (1) | AT337277B (en) |
| AU (1) | AU500019B2 (en) |
| BE (1) | BE828232A (en) |
| CA (1) | CA1055597A (en) |
| CH (1) | CH585994A5 (en) |
| DE (1) | DE2457492C2 (en) |
| DK (1) | DK168775A (en) |
| FR (1) | FR2268418B1 (en) |
| GB (1) | GB1506924A (en) |
| IT (1) | IT1032713B (en) |
| NL (1) | NL7405405A (en) |
| SE (1) | SE404121B (en) |
Families Citing this family (19)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2807986A1 (en) * | 1978-02-22 | 1979-08-30 | Hertz Inst Heinrich | SYSTEM FOR INTERACTIVE CABLE TV |
| CA1142244A (en) * | 1979-08-22 | 1983-03-01 | Eric J. Gargini | Wired broadcasting system with subscriber controlled switched programme selection |
| NL8006976A (en) * | 1980-12-22 | 1982-07-16 | Delta Kabel Bv | SWITCHING SYSTEM. |
| US4491983A (en) * | 1981-05-14 | 1985-01-01 | Times Fiber Communications, Inc. | Information distribution system |
| AT382276B (en) * | 1981-08-03 | 1987-02-10 | Elektromos Hiradastechnikai Ki | WITH AN ANTENNA SYSTEM FOR A DISTRICT ASSEMBLED TWO-WAY MESSAGE SYSTEM BETWEEN TWO OR MORE ANY PARTICIPANTS |
| GB2117210A (en) * | 1982-01-26 | 1983-10-05 | Kenneth James Fenning | Video transmission system |
| CA1177558A (en) * | 1982-04-15 | 1984-11-06 | Groupe Videotron Ltee. (Le) | Cable network data transmission system |
| GB2164229B (en) * | 1982-05-14 | 1986-08-20 | Communications Patents Ltd | Communications system |
| DE3382546D1 (en) * | 1982-05-14 | 1992-05-27 | Communications Patents Ltd | COMMUNICATION SYSTEM. |
| GB2127257A (en) * | 1982-08-17 | 1984-04-04 | Visionhire Cable Limited | Distribution apparatus |
| DE3246225C2 (en) * | 1982-12-14 | 1985-07-18 | ANT Nachrichtentechnik GmbH, 7150 Backnang | Broadband distribution system with a large number of channels |
| DE3339636A1 (en) * | 1983-11-02 | 1985-05-15 | Blaupunkt-Werke Gmbh, 3200 Hildesheim | Cable television system |
| FR2558674B1 (en) * | 1984-01-19 | 1988-05-06 | Telecommunications Sa | VIDEOCOMMUNICATION DISTRIBUTION NETWORK |
| NL8400860A (en) * | 1984-03-16 | 1985-10-16 | Nl Standard Electric Mij B V | CABLE TELEVISION NETWORK. |
| EP0167237A3 (en) * | 1984-05-31 | 1988-08-03 | AMERICAN TELEVISION & COMMUNICATIONS CORPORATION | Cable television system |
| GB8428647D0 (en) * | 1984-11-13 | 1984-12-19 | Communications Patents Ltd | Communication system |
| JP2658030B2 (en) * | 1987-01-30 | 1997-09-30 | ソニー株式会社 | Information transmission equipment |
| US4887152A (en) * | 1987-01-30 | 1989-12-12 | Sony Corporation | Message delivery system operable in an override mode upon reception of a command signal |
| DE3840254C1 (en) * | 1988-11-29 | 1990-06-07 | Neuberger Nachrichten- Und Antennentechnik Gmbh, 8000 Muenchen, De |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3639840A (en) * | 1969-11-28 | 1972-02-01 | Spencer Kennedy Lab Inc | Multicarrier transmission system |
-
1974
- 1974-04-22 NL NL7405405A patent/NL7405405A/en not_active Application Discontinuation
- 1974-12-05 DE DE19742457492 patent/DE2457492C2/en not_active Expired
-
1975
- 1975-04-15 CA CA224,652A patent/CA1055597A/en not_active Expired
- 1975-04-18 GB GB1607875A patent/GB1506924A/en not_active Expired
- 1975-04-18 CH CH500375A patent/CH585994A5/xx not_active IP Right Cessation
- 1975-04-18 DK DK168775A patent/DK168775A/en active IP Right Grant
- 1975-04-18 SE SE7504478A patent/SE404121B/en not_active IP Right Cessation
- 1975-04-18 IT IT6799675A patent/IT1032713B/en active
- 1975-04-21 AU AU80334/75A patent/AU500019B2/en not_active Expired
- 1975-04-22 BE BE155646A patent/BE828232A/en not_active IP Right Cessation
- 1975-04-22 JP JP4904175A patent/JPS604633B2/en not_active Expired
- 1975-04-22 FR FR7512482A patent/FR2268418B1/fr not_active Expired
- 1975-04-22 AT AT307775A patent/AT337277B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| JPS604633B2 (en) | 1985-02-05 |
| DE2457492C2 (en) | 1983-06-01 |
| SE404121B (en) | 1978-09-18 |
| FR2268418A1 (en) | 1975-11-14 |
| IT1032713B (en) | 1979-06-20 |
| FR2268418B1 (en) | 1982-05-28 |
| JPS512354A (en) | 1976-01-09 |
| SE7504478L (en) | 1975-10-23 |
| DE2457492A1 (en) | 1975-10-30 |
| NL7405405A (en) | 1975-10-24 |
| AT337277B (en) | 1977-06-27 |
| ATA307775A (en) | 1976-10-15 |
| AU500019B2 (en) | 1979-05-10 |
| BE828232A (en) | 1975-10-22 |
| GB1506924A (en) | 1978-04-12 |
| AU8033475A (en) | 1976-10-28 |
| DK168775A (en) | 1975-10-23 |
| CH585994A5 (en) | 1977-03-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |
Effective date: 19960529 |