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Thread: Television System Changes

  1. #1 Television System Changes 
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    I studied Television Engineering in the early '60s, when the system undoubtedly was rather different than today; this is the reason for my thread, to learn what has significantly changed. Surely, there are others who, like me, would learn a lot from the newer methods. If I attempted to research this to find answers, the enormous amount of info presented would likely not be all studied before I leave this world!

    Back then, an "Image Orthicon" scanned the scene to be transmitted, locking each individual scan of every frame sent to "synch" in-step with the viewer's CRT. Early-on, raster brightness was found to be unacceptably diminishing from upper-left down to lower-right, due to short phosphorescence persistence; thus, "interlaced scanning" was introduced.

    Large-screen projection-type sets were introduced perhaps in the '80s; were they still of the older type of transmission system? Earl Muntz sold a large-screen T-V, perhaps 28", around 1950. My grandparents had one. It's clarity was notably poor, as the lines were very wide, and only (a guess) about 300 of 525 were actually being displayed! Vertical deflection was always a sore point, the early round-screens giving way to the familiar "oblong" shape, which clipped viewability, if there was any, of the top and bottom of the frame. High-voltage requirements, 20KV or more, were also an ongoing problem, the "flyback" transformers screaming away at 15,750 HZ, also delivering energy to a high-voltage vacuum tube rectifier.

    I think digitizing the scene info must now be done differently, maybe without scanning lines at all? How, then, was newer technology phased-in with the old: were the old analog sets made obsolete? How was this made acceptable to the viewing public? I gather the "CMOS" device was at the heart of the change, originally; is it still of importance, or supplanted with yet something newer?

    I have zillions of similar imponderables which have troubled me, but this should be enough for a start! Thank you for reading! jocular


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    Quote Originally Posted by jocular View Post
    I studied Television Engineering in the early '60s, when the system undoubtedly was rather different than today; this is the reason for my thread, to learn what has significantly changed. Surely, there are others who, like me, would learn a lot from the newer methods. If I attempted to research this to find answers, the enormous amount of info presented would likely not be all studied before I leave this world!
    Nice to meet another old-timer! A neighbor of mine was a TV repair technician. Although he wasn't formally educated much beyond high school, he had a good working knowledge of TV systems, which he was kind enough to impart. I'll never forget how he explained that NTSC really stood for "never twice the same color."

    I think digitizing the scene info must now be done differently, maybe without scanning lines at all?
    The same 2D imaging array technology you find in your home camera is used -- albeit at a higher level of sophistication -- in broadcast video. Scanning still occurs, after a fashion, as data is generally read out of the array in serial fashion. But the type of artifacts produced are different from those generated by the old interlaced system.

    How, then, was newer technology phased-in with the old: were the old analog sets made obsolete?
    Unlike the transition from black and white to color, there was no gentle phasing in of digital TV. The signal structures are simply too different, so backward-compatibility was never seriously considered as a goal. The transition to digital was by fiat. One day, the analog TV signals simply went away. Older sets could still be used, but required the addition of a converter box. To help ease the transition in the US, the government subsidized the converter boxes for a time. Where I live (in California), my old analog TV can still pick up a couple of Mexican channels in the UHF band. But I believe all US transmitters have converted to the digital format.

    How was this made acceptable to the viewing public?
    Well, I know of a lot of people who are still grumbling that they had to buy new gear. But technology moves on.

    I gather the "CMOS" device was at the heart of the change, originally; is it still of importance, or supplanted with yet something newer?
    CMOS is the mainstream type of integrated-circuit technology. Its chief virtue is its low cost. Most consumer-grade cameras use CMOS imagers. The pros (and that includes astronomers) still use CCDs, for the superior dynamic range. But sustained effort by manufacturers have pushed CMOS to levels of performance well beyond what was expected by "reasonable" folk a decade ago.

    I have zillions of similar imponderables which have troubled me, but this should be enough for a start! Thank you for reading! jocular
    Thanks for your questions! It was fun remembering the many hours I spent as a kid, poking around the innards of my neighbor's TVs. I learned to respect the high-voltage section in particular. Getting bitten by 25kV 16kHz juice tends to make a lasting impression!


    Last edited by tk421; June 21st, 2013 at 11:35 AM. Reason: fixed typos
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    How was this made acceptable to the viewing public?
    The public didn't have any choices about what was shoved down their throats by the big businesses of the time and were forced into buying new sets or not get a very good or more programing picture. This is done for them to insure they can extract more of your income because before you got to watch TV for free and they made their BILLIONS from the advertising they produced. So instead of the businesses paying for TV, now the public does to the most extent with advertisers also being soaked as well.
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    Quote Originally Posted by tk421 View Post

    I have zillions of similar imponderables which have troubled me, but this should be enough for a start! Thank you for reading! jocular
    Thanks for your questions! It was fun remembering the many hours I spent as a kid, poking around the innards of my neighbor's TVs. I learned to respect the high-voltage section in particular. Getting bitten by 25kV 16kHz juice tends to make a lasting impression!
    You cannot know how enlightenment helps me! Thank you kindly! A few more then: "CCD" : an unfamiliar term. When my folks got a color set, I secreted the old Philco downstairs to my basement "lab", removed everything from the cabinet, and mounted the CRT in the wall of the hollow under the basement stairs. By that time, I was perhaps 13 or so, and well-versed in the messing-around with of neon sign transformers, so never allowed myself to get the classic T-V "Ultor" bite! Regulation is so poor, that voltage drops instantly, likely to well-below lethal level, but I imagine the sting is quite pronounced!

    Were you ever concerned by the warning notices posted on the cabinet backs advising of the radiation hazard? Soft X-rays, to be sure, but the thick glass front and phosphors of the CRT seemed to limit radiation in that direction. Nonetheless, our old Philco, and I suspect most other makes, had a thick, about 3/8" flat glass plate in front of the CRT, to boot! Advent of color upped anode requirement to, I believe, 30-40KV, which surely increased radiation produced. My first real job, after graduating from DeVry Technical Institute was with Motorola in Melrose Park, Illinois, as a "Phasor" on a moving belt line converging the 3 guns while watching in continuous mirror on the opposite side. My concern for radiation, and the gruelling side-step slow walking, following the damn things along the line quickly curtailed my employment there! jocular
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    Quote Originally Posted by cosmictraveler View Post
    How was this made acceptable to the viewing public?
    The public didn't have any choices about what was shoved down their throats by the big businesses of the time and were forced into buying new sets or not get a very good or more programing picture. This is done for them to insure they can extract more of your income because before you got to watch TV for free and they made their BILLIONS from the advertising they produced. So instead of the businesses paying for TV, now the public does to the most extent with advertisers also being soaked as well.
    No doubt about the consumer being bilked, as usual. One communications change as a result of the cell technology really ticks me off: A long-distance call before cells was paid for by the CALLER, the receiver paid nothing beyond his normal usage fee, no matter where the call originated. Today, caller pays, receiver pays, minutes charged, and at the other end of the slave-tether is the fact that the public was led to believe that breaking up Ma-Bell in 1984 would reduce their phone bills! Ha! Just the opposite! Plus, the "Bells" gradually, but almost clandestinely, got back together again, in various ways. Southwestern Bell Telephone, which became SBC, directly and indirectly controls over half of the land-lines in the United States! The cell movement really bit them all in the ass, however, as land-lines became more and more unused. AT&T invested untold millions in long-distance towers, which became basically obsolete as fiber-optics took over. Some of those towers may have hopefully been salvaged for cell use. Sorry for going off-thread here! jocular
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    Quote Originally Posted by jocular View Post
    You cannot know how enlightenment helps me! Thank you kindly! A few more then: "CCD" : an unfamiliar term.
    Oh -- sorry! Since you were familiar with "CMOS," I'd mistakenly assumed that you knew all abbreviations beginning with a "C."

    CCD stands for "charge-coupled device." CCD imagers are arrays of MOS capacitors, with a surface exposed to light. Photogenerated electrons are trapped in a potential well near the surface, and can be shuttled to adjacent cells in a bucket-brigade fashion by adjusting voltages on electrodes (analogous to the gate terminal of a MOSFET). The depth of the well is such that very few electrons are lost (transfer losses are denominated in parts per million). Sensitivity can be traded for speed, as these cells integrate the total light incident upon them. That attribute, plus the low noise of the sensor at cryogenic temperatures, makes CCDs highly attractive for applications requiring high senstivity (as in astronomy).

    When my folks got a color set, I secreted the old Philco downstairs to my basement "lab", removed everything from the cabinet, and mounted the CRT in the wall of the hollow under the basement stairs. By that time, I was perhaps 13 or so, and well-versed in the messing-around with of neon sign transformers, so never allowed myself to get the classic T-V "Ultor" bite! Regulation is so poor, that voltage drops instantly, likely to well-below lethal level, but I imagine the sting is quite pronounced!
    The capacitance of the CRT is large enough to cause a non-trivial "charge transfer event." Let's just say that I confirmed that the human nervous system has some sensitivity to electricity.

    Were you ever concerned by the warning notices posted on the cabinet backs advising of the radiation hazard? Soft X-rays, to be sure, but the thick glass front and phosphors of the CRT seemed to limit radiation in that direction. Nonetheless, our old Philco, and I suspect most other makes, had a thick, about 3/8" flat glass plate in front of the CRT, to boot! Advent of color upped anode requirement to, I believe, 30-40KV, which surely increased radiation produced. My first real job, after graduating from DeVry Technical Institute was with Motorola in Melrose Park, Illinois, as a "Phasor" on a moving belt line converging the 3 guns while watching in continuous mirror on the opposite side. My concern for radiation, and the gruelling side-step slow walking, following the damn things along the line quickly curtailed my employment there! jocular
    The x-rays from the back of larger color CRTs definitely scared my neighbor (and, therefore, me). He advised spending as little time in the back of powered-on sets as possible. He told me stories -- never verified, but plausible -- of people taking crude x-ray photographs using the emissions from color TVs. I have no desire to run the relevant experiment, so I'll have to take his word for it. Now that you've brought up the subject, I might have to sit down and do some rough calculations to see if the claim has merit...
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    Quote Originally Posted by tk421 View Post
    [


    The capacitance of the CRT is large enough to cause a non-trivial "charge transfer event." Let's just say that I confirmed that the human nervous system has some sensitivity to electricity.

    Were you ever concerned by the warning notices posted on the cabinet backs advising of the radiation hazard? Soft X-rays, to be sure, but the thick glass front and phosphors of the CRT seemed to limit radiation in that direction. Nonetheless, our old Philco, and I suspect most other makes, had a thick, about 3/8" flat glass plate in front of the CRT, to boot! Advent of color upped anode requirement to, I believe, 30-40KV, which surely increased radiation produced. My first real job, after graduating from DeVry Technical Institute was with Motorola in Melrose Park, Illinois, as a "Phasor" on a moving belt line converging the 3 guns while watching in continuous mirror on the opposite side. My concern for radiation, and the gruelling side-step slow walking, following the damn things along the line quickly curtailed my employment there! jocular
    The x-rays from the back of larger color CRTs definitely scared my neighbor (and, therefore, me). He advised spending as little time in the back of powered-on sets as possible. He told me stories -- never verified, but plausible -- of people taking crude x-ray photographs using the emissions from color TVs. I have no desire to run the relevant experiment, so I'll have to take his word for it. Now that you've brought up the subject, I might have to sit down and do some rough calculations to see if the claim has merit...
    The big CRTs of course ARE a capacitor, with conductive coating inside and out; the inside coating being very highly positively charged, to attract each and every electron striking the fluorescent screen surface away from it, to prevent negative charge build-up on the screen. But, you yourself know all this, just mentioning for sake of those interested. I had a CRT stored in the attic for 6 months, after which time a jumperr across the coatings produced a visible spark! Very efficient capacitor, indeed!

    Regarding X-ray production, my homebuilt fluoroscope using an old Coolidge Tube (not rotating anode), at 90KV and 5ma, easily revealed bone structure within the hand, at distance at least 10 feet from the tube. Personally, I doubt the X-ray photograph claim about T-V back-ends, considering the relatively lower voltage, much lower beam current (hence, X-ray intensity), and inverse square law (distance from source). Interesting point to consider: folks often were advised to keep children viewers back away from the screen; perhaps young eyes are more susceptible to radiation damage? When as a teen-ager, I messed with the fluoroscope, I "wore" a 1/8" thick soft lead sheet in front of my pants, suspended from my belt.....concerned even then with damage to quickly reproducing cells. No lasting effects are evident 55 years later, and the "goods" still work! What madness I involved myself with, today I wonder that my poor parents managed to live with, and allow it! jocular
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    Forum Radioactive Isotope cosmictraveler's Avatar
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    I do not use any cable or satellite services any longer and only watch what I can receive for free where I live, which isn't a whole lot, but better than nothing. I refuse to pay to watch mostly infomercials, talk shows, musical shows and travel shows with only a few good TV shows actually being shown. So while I may be not seeing some stuff that I'm sure I'd enjoy, I am not throwing my money away either. To bad they don't allow you to choose which programs that you'd want to see and pay only for them like one dollar a month per show or something like that.
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    Quote Originally Posted by cosmictraveler View Post
    I do not use any cable or satellite services any longer and only watch what I can receive for free where I live, which isn't a whole lot, but better than nothing. I refuse to pay to watch mostly infomercials, talk shows, musical shows and travel shows with only a few good TV shows actually being shown. So while I may be not seeing some stuff that I'm sure I'd enjoy, I am not throwing my money away either. To bad they don't allow you to choose which programs that you'd want to see and pay only for them like one dollar a month per show or something like that.
    IMO, very few T-V offerings today are appealing enough to justify the amount of time wasted during all the interrupting commercials. One or two channels we receive are commercial-free during films. jocular
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    Quote Originally Posted by jocular View Post
    IMO, very few T-V offerings today are appealing enough to justify the amount of time wasted during all the interrupting commercials. One or two channels we receive are commercial-free during films. jocular
    Yes, it does seem as if a lot of TV is a series of adverts only occasionally interrupted by programs, at least in the US...
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