CA1052446A - Wired broadcasting system with a wideband coaxial cable for multi-channel signals - Google Patents

Abstract

BE IT KNOWN THAT I ERIC JOHN GARGINI a British Subject of 72 Fairway Avenue, West Drayton, Middlesex, England having made an invention entitled:-IMPROVEMENTS IN OR RELATING TO WIRED BROADCASTING SYSTEMS
the following disclosure contains a correct and full description of the invention and of the best mode known to the Inventor of taking advantage of the same.

ABSTRACT
A wired broadcasting system is provided which comprises a wideband coaxial cable for carrying multi-channel programme signals from at least one programme source to a plurality of exchanges to each of which a plurality of subscriber units are connected. The programme source provides signals on the cable stacked one upon the other in frequency. Each exchange comprises in respect of each subscriber a switchable frequency translator for selectively trans-lating 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.

Description

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The present invention relates to wired broadcasting systems.

I According to the present invention, there is provided a wired broadcasting system comprising a wideband coaxial cable for carrying multi-channel programme signals from at least one programme source to a plurality of exchang,ers to each of which plurality of subscriber units for receiving a particular fre-quency band are connected, the said at least one programme source being constructed to supply the signals to the cable in different frequency channels, and each exchange comprising for each subscriber a switchable frequency translator for selectively translating any one of the said frequency bands to a predeter-mined other frequency band receivable by the subscriber unit, switching means controllable from the respective subscriber unit `~
to selectively switch the frequency translator, and an output circuit constructed to supply the said predetermined other frequency signal to a feeder cable to which the subscriber is connected, a selector unit at each subscriber unit for generating control tones, wherein said switching means located at the ..... ..
exchange is responsive to said tones, a tone generator unit `
constructed to provide at least one master pilot tone to the said wide band coaxial cable, and a tone extractor unit at each exchange constructed to extract the said at least one master -pilot tone from the said wideband coaxial cable for application to each subscriber unit connected to the exchange, the selector unit comprising tone generators responsive to the said at least master pilot tone.
Each of the subscribers may be connected to -the res-pective 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 ,:

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particularly advantageous arrangement for a system where HF :~
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. signals are sent .~rom exchange.s~ Alternclti.vely, tlle su~)scribers may be corulected to their respec-tive exchaage by a coml~on cable~ in tlhich case -the said other :t`requency is diffe.rent .~or each subscr.ibera '.

q`he switching means located at the exchange rna~
be controlled by tones from a selector unit at the sub-scriber unit. rr`he selector unit ma~ comprise harmon.ic a~d divider generators locl~ed to a.master pilot tone or tones provided to the subscriber from the excha~geO

If it is desired to prevent a subscriber from selecting a particular programme or programmes9 means may be provided to prevent the.or one or more o~ the maæter pilot tones reaching the su.bsc.riber, thereby disabling one or more oX -the harmonic and divi.dex generators and mal~ing it impossible for the svbscriber to provide the necessary selection tone or tones to seleot the programme or programmes.

Embodiments of the present in~ention will now be described~ by way of example, with reference to ~he accompanying drawings; in wllich:

~ ig~l schematically illustrates an embodiment of the invention in which a plurali.ty of subscribers are li~ed to an exchange by separate respective cables;
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2 schematically illustxates a further embodiment of the inY~ntion ~~ ich a plurality of ~u.~sc.ribers are l mked to an exch~e by a common cable O . '~

Re~'erring to ~ig. 1, a programme car.rier signal generator 1 which comi)rises master fxequency gene.rators and ~0~O modulators is provlded with sound and vision pro~ramme sig~als on inputs 2, ~'he signal generator 1 transmits programme sig~als on low deviat-ion frecluenc~
modulatecL carriers stacked one upon the other in l.crequency to a wide band coaxial cable 3 which is in t~rn connected, to a plurality of exchanges 4 only one of which is shown~
~ow deviation F~Mo carriers are used as this reduced the 'problem of intermodulation distor-tion in frequency -trans-lators and permits adjacent chan~el selection after -t.rans--lation to a lower frequency band. ~lternatively l~.ere the problem of intermocluJ.ation distortion may be reduced by controlled frecluerLcy banc~ fi].terin.g the programme carrier signal generator may include stal~dard V~ and ~HF modulators. ~he cable ~ may have a bandwidth of for example 600 MEz. A tone generator unit 5 controlled b~ a~ i~put 6 is located between the signal generator 1 and the cable 3 and arranged to provide to the cab].e 3 one or more mast;er pilot tones., Each exchan~e 4 is co~nected to a plurali-t~ of ~ubscriber units 7 (only one of which is shown) b~

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respective ones o.~` a plllrality o~ two or four w:i.re k~
~Qwist' c~les~ such as are described in oux Paterlt Spec:i.~ical;ioll Nou 1,272,59/l. Each su~scribe~ cable 8 is co~.mected to a respective o~e of a seri.es of baluns li~ed to a respec-tive one of a series of fretluency trc-~slators 10 arr~nged to translate the carrier frequencies to a fre~uency acceptable -~o .the subscri.bers unit. A tone extractor and control unit 11 i.s arranged to extract -the master pi.lot tone or tones provided by the unit 5 and apply them to the baluns 9.
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Each subscriber unit Gomprises a receiver 12 adapte~ to receive the ~ or ~ signals and a programme .selector 13 which may compri.~e a bank of push buttons 14, actuation of which provides one or more selection ton.es to the e~change along the respective cclble 80 The .æelection tones or Xrequencies are generated by hc~moni.c and divlde~ generators locked to the master pilot to~.e or tones se~t from the baluns 9 in the exchan~e l~ along either of the palrs of wires in the cable ~.
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When a subscriber wishes to receive a particular progra~e, he p.resses an appropriate push-button generating the required tone which identifies -the frequency channel in the cc~ble 3 on ~lhich tha-t; programme is provided. ~he frequellcy tra~slator and ballul syste~ of the subscriber ;, : ,:: , . " . . . .- .
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assoc,iated with that -tone or tones i5 transla-ted from the ba~d occupied on the coaxial cable 3 to the low frec,~uency band reqvired by the subscribers u~it 70 ' ', . ' ' ' ' '' Where only one master tone is pro~ided o~ the li~ 3 b~ the unit 59 the sub~Griber can be denied all the progra~mes on the line by preventing t'he ma~ter to~e being transmitted to him from the exchange via -tone ~xtractor arld control u~it 11, the absence of the master tone clisabling the selec,tor 130 Where more than one maæter tolle is provided, particular programmes or groups of programmes can be denied to ~ subscriber whils-t other programmes or groups of programmes are supplied, by preventi~g the tra~smissi.on of selected ones of the ' 'master tones from the exchange to..the subscriber~ ~his æelective denial facility may be usef~ æystems where for e~ample payment ~or some but not all of the pxogrammes ~:' is requ.ired, or where access to particular programmes has :-~to be li~ited ~or security reasons.
:, , Where the to~es are associated with programmes ~or whish additio~al pa~ment is required th`e corresponding tone generator ma~ be inhibited until the subscriber takes some action to inclicate that he has paid or is pxepared to accept payment for receiving the programmeO Alter~atively ~ 6 --, , .

se:l.ectio~ of a "pay" progrratmne may autornati.cc311y i.ndicat;e that pa~mer.~t ~ accep-ted~ In one application all tone extrac-tor a~1d control ~lits 11 may be v~lder the control of a cen-tral pay ~V com~uter a~d the co-mpute.r may generate si~n.als such as digital information over ths k 3 or a secondary connectionO

~ eferring now to Fig. 2, an alternative arrange~
m~nt i.s shown in which the i.ndividual cables 8 o~ ig. 1 are replaced by a wide band coa~ial ca~l.e 15 commo~ tv all of the subscribers co~n.ected -to a particular e}~change 4. Corresponding co~ponents of` the ~ig. 1 a~d l~ig~
embodiments are given corresponding reference ~umexals~

~ ach subscriber is li~ked by a subsidi.ary coc~xial cab:Le lG to the main cable 15, and is allocated a particular frequency band i.n the cables 15 and 16~ Subscribers near to the e~ch~ngc are allocated high frequency bauds and subscribers remote from the excha~ge are allocated low ~reque~cy bands to ob-tai.n a maximum reach for excha~ges at a given sending level~

The excha~ge 4 is similar to that described ~ith re~erence to ~igo 1 but i.ncludes in respect of each sub~-scxiber a characteristic fxeque~cy geuera-tor to provide sel~cted programme signals on an ~o~l- carrier~ VEF or UEF sta~dard ~ravefor~ns could alternatively be provided~
~he subscxiber unit is also similar to that described ~r.ith refere~ce to ~igD 1~ bu-t additio~all~lcludes ~ ,, : .

r.ecluency ~ranslator for transla-ting the characteristic carr:ier -~o a frequency accepta~le to th~ subscril:~ers rece:Lver 12~ and &. c}laracteristic selectioll tone ~eneratcr 1~, the e~change being arranged on receipt of the characteristlc selection tone -to alloca-te the frequency of a selectecl programme signal to a band dedicated to the particular subscriber. ~he local oscill~.~tors of the subscribers frequency txv~lslator may be controlled by pilot slgnals sent from the exchange to increase -the security of the system. ~lternativel~ or in addition this translator cc~ be located outside the subscribers premises~ for example on the pole route -outside the premises, or a-t the end of the road in - which the premises are located~

Alter~a:tive arr~n~ements to those illust.rated may of course be provided. ~or example~ provision ~y be made for the ~ariable tuning o~ exchanKe filters upon receipt of single or combination tone lrequencies from the subscriber selector u~it.

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Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A wired broadcasting system comprising a wideband coaxial cable for carrying multi-channel programme signals from at least one programme source to a plurality of exchangers to each of which plurality of subscriber units for receiving a particular frequency band are connected, the said at least one programme source being constructed to supply the signals to the cable in different frequency channels, and each exchange com-prising for each subscriber a switchable frequency translator for selectively translating any one of the said frequency bands to a predetermined other frequency band receivable by the sub-scriber unit, switching means controllable from the respective subscriber unit to selectively switch the frequency translator, and an output circuit constructed to supply the said predetermined other frequency signal to a feeder cable to which the subscriber is connected, a selector unit at each subscriber unit for generating control tones, wherein said switching means located at the exchange is responsive to said tones, a tone generator unit constructed to provide at least one master pilot tone to the said wide band coaxial cable, and a tone extractor unit at each exchange constructed to extract the said at least one master pilot tone from the said wideband coaxial cable for application to each subscriber unit connected to the exchange, the selector unit comprising tone generators response to the said at least one master pilot tone.

2. A wired broadcasting system according to claim 1, comprising selective transmission means at each exchange for preventing the said at least one master pilot tone from reaching the subscriber tone generators.