Week 6: Television and Cable
Week 6: Television and Cable Com 2400
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This 6 page Class Notes was uploaded by Rio Frohriep on Tuesday October 20, 2015. The Class Notes belongs to Com 2400 at Western Michigan University taught by Kayany in Summer 2015. Since its upload, it has received 12 views. For similar materials see Intro to Media and Telecom in Communication Studies at Western Michigan University.
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Date Created: 10/20/15
Intro to Media and Telecommunications Whereas radio was impressive to say the least it was not a major scientific breakthrough w When light passes through the element Selenium SE a proportionate electric current is generated Joseph May The man to first discover this phenomenon This was the basis for the first television Photoelectric cells are made up of selenium When electricity is passed through them they capture the image in terms of light vs dark and carries that image via radio wave How a Television Camera Captures and Image The camera lens captures the image in front of it and transmits it onto the screen behind it This image is scanned line by line Each point of light on the line passes through a selenium cell creating a proportionate electric charge This electric charge is then transmitted through the air like in radio The more lines scanned the better the quality of the image Mechanical Television Paul Nipkow invented a mechanical scanner that used a rotating metal desk to record the image John Baird in the UK Charles Jenkins in the US established mechanical television systems BBC British Broadcasting Company started with mechanical television systems Rotating disk with Second disk rotating at the spiral at holes V same speed Screen 30 Eo 39 39l I c a y se mum o w 3 i cells Light 0 1 l l I a l 0quotquot O O 112 39 X i l l r w 6 image 0 3 l I 39l D l I y quot 7 1 Wire 39 39 39 C O LT The scan occurs 24second in order to simulate movement The image is recreated on the screen on the receiving end CameratoSet Relations The television cameras and sets have to be in perfect sync If the camera captures an image with 200 lines at 20 scanssecond the TV set must also be set to recreate the image at the same speed If it is not the set will simply not work Phosphors The inside of the TV screen is coated with phosphors When the electron beam strikes the phosphor it makes the screen glow On a blackwhite screen there is only one phosphor that glows white when struck On color sets there are three Red Green and Blue RGB Philo Farnsworth s Electronic Scanners aka Image Dissector First one to propose scanning the image with an electron beam instead of Selenium VK Zworykin s lconoscope David Sarnoff hired VK Zworykin to develop the television Zworykin developed the lconoscope lconoscope The lconoscope was the first practical video camera tube to be used in early television cameras The iconoscope produced a much stronger signal than earlier mechanical designs and could be used under any weit conditions definition from Wikipedia Electronic television had a much better image RCA debuted its TV during the World s Fair in 1939 FCC allocated a band of frequencies for TV dubbed VHF Very High Frequency After WWII the TV Gold Rush began 100 stations were on the air by 1950 All the allotted frequencies were used up very quickly and in 1948 the FCC put a freeze on all Television license applications First Television Frequencies VHF Very High Frequencies is the name for radio frequencies from 30MHz 300MHz TV Channels 2 13 UHF Ultra High Frequencies is the name for radio frequencies from 300MHZ BGHz TV Channels 1464 Rabbit Ears FCC s 6 th report and order in 1952 FCC allocated new frequencies for TV to meet the demand UHF Also Established the national standard National Television Standard All Television Sets in the country must broadcast at one standard NTSC National Television Systems Committee An industrywide committee of engineers that FCC established to make recommendations on standards NTSC recommended a 525 lines at 30 framessecond system which was the standard until 2008 This standard provides acceptable image quality without using up too many frequencies per channel Different Television Systems NTSC National Television Systems Committee 525 lines using 45 MHz FM audio AM visual North America PAL Phase Alternate Line 625 Alternate lines using 65 MHz FM Audio AM visual UK and Western Europe SECAM Sequential Couleur Meire 625 lines using 65 MHz AM adio FM visual France Russia Eastern Europe Color Television Scanning is based on same principal of BW television Camera scans amount of RGB and transmits them separately CBS was the first to develop a color system 343 lines at 20 framessecond Used Mechanical System Not compatible with existing BW Systems FCC rejected it RCA all electronic coor system Compatible with preexisting BW systems FCC adopted this as the national standard in 1953 H DTV Broadband relay systems reduced TV s dependence on electromagnetic spectrum space It became possible now to improve picture quality because the worry of bandwidth was null ATSC Advanced Television Systems Commitee New group to make TV recommendations for standards Now that there was no need to worry about TV taking up too many frequencies the FCC could establish a new standard to accommodate a better picture quality Hence they established the ATSC In 1982 ATSC was established to study the possibility of a new standard However the FCC didn t want to adopt the new HD standard in 82 because that would render the old TV s useless On June 12 2009 the NTSC standard was replaced by the new ATSC standard All broadcasts would be in HDTV However for those that didn t want to buy a new television set they could simply buy a converter box which would adapt the HD signal into the old system so it could be read by the old TVs Digital Signal vs Anolog Analog signals send the radio waves through the air Digital signals only send the measurements of the waves through the air The continuous analog signal is simply measured and converted to a binary code That code is then transmitted and translated on the receiver end Television Systems Out Today not including those that are considered obsolete HDTV Digital Signal Aspect ratio 16 9 same as in a movie theatre Horizontal lines range from 7201080 Pixel elements rather than scanning lines 1280x720 1920x1080 resolution Requires 36MHZ bandwidth for a full signal 6x what was required previously Plasma TV Phosphors are lit by superheated charged gas All the pixels can be lit at once not line by line No cathoderay tube this is a very thin model LCD Liquid Crystal Display Pixels are turned onoff at a specific refresh rate most often 60th120th of a second Constant backlight when a pixel is turned off it doesn t allow the backlight to show through LED Light Emitting Diode Same as LCD but the backlight is replaced by LED as oppose to florescent OLED Newest as of 2015 No Backlight Pixels illuminate on their own WHO BOUGHT WHO Rupert Murdoch s News Corps and Fox Network in 1986 Disney boughtABC in 1995 Westinghouse bought CBS in 1995 Viacom bought it in 2001 General Electric bought RCA and NBC in 1985 Comcast bought NBC in 2015 CABLE TELEVISION History of alternate deliver methods for television CATV Community Antena Television Public antenna that anyone in a community could connect to for a fee Started in Oregon and Pensilvania in 1948 By 1952 70 cable systems were serving 1500 houses Distant Signal Import Better antennas cable providers could pick up signals from neighboring cities Cable vs Broadcasting WARM At first local broadcasters didn t mind Cable carriers They found it as a way to reach bigger demographics However once cable started dropping programs from some stations and picking up others the local broadcasters started having a problem At first the FCC avoided regulating cable deciding it was really just a service to broadcast TV In 1972 FCC established more formal Rules Local communities states and the FCC were to regulate cable Cable stations MUST CARRY all of the local stations to their entirety The import of distant signals would be regulated
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