In the 1950s , there were fourtelevisionnetworks in the United States . Because of the frequencies lot to telly , the signals could only be take in in a " lineage of sight " from the transmitting feeler . People subsist in remote domain , especially remote cragged areas , could n’t see the programs that were already becoming an important part of U.S. refinement .
In 1948 , people living in distant valleys in Pennsylvania solved their reception problem by arrange antennas on hills and running cables to their houses . These 24-hour interval , the same engineering science once used by remote Hamlet and select urban center allow watcher all over the land to get at a across-the-board variety of programs and channels that foregather their individual needs and desires . By the early 1990s , cable television receiver had pass nearly half the home in the United States .
Today , U.S. cable television system give birth hundred of groove to some 60 million homes , while also provide a grow issue of mass with high - upper Internet access . Some cable system even allow you make telephony calls and incur fresh programing technologies ! In this article , we ’ll show you how cable television bring you so much information and such a wide range of programs , from educational to inspirational to just plain funny .
" In a line organisation , the signal might have choke through 30 or 40 amplifiers before reaching your menage , one every 1,000 foot or so , " Wall says . " With each amplifier , you would get noise and distorted shape . Plus , if one of the amplifiers failed , you lost the picture . Cable got a reputation for not having the good quality picture and for not being reliable . " In the belated 1970s , line television would detect a solution to the amplifier problem . By then , they had also develop engineering that allowed them to add more programming to cable inspection and repair .
Adding Channels
In the other 1950s , cable television service systems began experimenting with way to utilize microwave oven beam and receiving towers to seize the signals from distant stations . In some cases , this made telly available to people who survive outside the range of stock broadcasts . In other cases , especially in the northeastern United States , it imply that cable customers might have access to several broadcast stations of the same web . For the first prison term , overseas telegram was used to enrich telly consider , not just make ordinary viewing potential . This depart a style that would start to blossom fully in the seventies .
The addition ofCATV(community aerial idiot box ) Stations of the Cross and the spread of cable systems ultimately led manufacturers to add aswitchto most fresh television system sets . People could do their televisions to tune to television channel based on theFederal Communications Commission(FCC ) frequency allocation plan , or they could set them for the programme used by most cable system . The two program differed in important ways .
In both tuning system , each television system place was given a 6 - megacycle ( MHz ) gash of theradio spectrum . The FCC had earlier devoted parts of thevery high frequency(VHF ) spectrum to 12 telecasting channels . The channels were n’t put into a unmarried cylinder block of absolute frequency , but were or else broken intotwo groupsto avoid interfere with existingradioservices .
Later , when the get popularity of television necessitated additional television channel , the FCC allocated frequencies in theultra - in high spirits frequency(UHF ) portion of the spectrum . They set up channels 14 to 69 using a block of frequencies between 470 MHz and 812 MHz .
Because they used cable television service instead of antenna , cable television systems did n’t have to worry about existing services . Engineers could use the so - called mid - band , those frequencies clear over by broadcast TV due to other signals , for canal 14 - 22 . Channels 1 through 6 are at low relative frequency and the eternal rest are higher . The " CATV / Antenna " switch tells the television ’s tuner whether to tune around the mid - band or to strain straight through it .
While we ’re on the subject of tuning , it ’s worth considering why CATV systems do n’t use the same frequencies for stations broadcasting on channels 1 to 6 that those stations utilize to broadcast over the airwave . Cable equipment is designed toshieldthe signals carry on the cable from extraneous hindrance , and television are designed to accept signal only from the point of connection to the cable or antenna ; butinterferencecan still go in the system , especially at connection . When the interference comes from the same channel that ’s carry on the cable television service , there is a problem because of the difference in broadcast speed between the two signals .
radio set signals travel through the air at a speed very close to thespeed of light . In acoaxial cablelike the one that take CATV signal to your house , wireless signals trip at about two - third the speed of light . When the program and cable television signals get to the television tuner a fraction of a second apart , you see a double mental image call in " ghosting . "
In 1972 , a cable television service arrangement in Wilkes - Barre , PA , start offering the first " pay - per - prospect " communication channel . The customer would yield to watch case-by-case moving-picture show or sporting event . They called the young serviceHome Box Office , orHBO . It continued as a regional help until 1975 , when HBO began transmitting a signaling to a satellite ingeosynchronous orbitand then down to line systems in Florida and Mississippi . Scientific - Atlanta ’s Bill Wall says that these early satellites could receive and retransmit up to 24 channel . The cable systems receiving the signal used looker feeler 10 meter in diameter , with a separate sweetheart for each channel ! With the beginning of planet course of study pitch to overseas telegram systems , the canonic architecture of the mod cable arrangement was in place .
As the number of computer program selection grew , thebandwidthof cable systems also increased . Early systems operated at 200 megahertz , allowing 33 channel . As technology progressed , the bandwidth increased to 300 , 400 , 500 and now 550 MHz , with the telephone number of channel increasing to 91 . Two additional advancement in engineering – fiber optics and analog - to - digital transition – improved features and broadcast tone while continuing to increase the bit of channels uncommitted .
The Glass Cable
In 1976 , a new sort of transmission line arrangement debut . This system usedfiber - optic cablefor thetrunk cablesthat carry signal from the CATV head - end to neck of the woods . Thehead - endis where the cable system receives scheduling from various source , assigns the computer programing to channels and retransmit it onto cables . By the previous 1970s , character opticshad progressed well and so were a toll - effective way of carrying CATV signaling over foresighted distance . The great advantage of vulcanized fiber - optic cable is that it does n’t suffer the same signaling loss as coaxal cable , which eliminated the need for so manyamplifiers . In the early vulcanized fiber - optic cable systems , the turn of amplifier between head - destruction and customer was reduced from 30 or 40 down to around six . In systems follow out since 1988 , the number of amplifier has been further reduced , to the point that only one or two amplifiers are required for most customers . Decreasing the figure of amplifiers made dramatic improvements in signal quality and system dependableness .
Another benefit that came from the move to fiber - optic cable was greatercustomization . Since a single fiber - optic cable might serve 500 households , it became possible to target individual neighborhoods for content and services . In the nineties , cable television providers found this same neck of the woods group to be ideal for make alocal - region networkand providing Internet access throughcable modems .
In 1989,General Instrumentsdemonstrated that it was possible to win over an parallel cable sign to digital and convey it in a standard 6 - megahertz television epithelial duct . UsingMPEG compression , CATV systems install today can channelize up to 10 channels of video in the 6 - MHz bandwidth of a single parallel television channel . When combined with a 550 - MHz overall bandwidth , this allows the opening of nearly1,000 channelsof telecasting on a system . In gain , digital technology allows for error correction to ensure the character of the receive signaling .
The move to digital technology also changed the lineament of one of cable television receiver ’s most visible feature of speech : the scramble groove .
The first system to " scramble " a channel on a cable system system was demonstrated in 1971 . In the firstscramblingsystem , one of the signals used to contemporize the tv photo was removed when the signal was transmitted , then reinserted by a humble gadget at the client ’s house . Later scrambling systems infix a signaling slightly set off from the channel ’s relative frequency to interfere with the picture , then filtered the interfering signal out of the mix at the client ’s idiot box . In both cases , the scramble channel could generally be seen as a jagged , jumbled set of video images .
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