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#91
10-19-2005, 11:38 PM
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IMHO, the FCC really jumped the gun on HDTV and DTV. Hey look, the standard was hammered out in '98. Well, video codecs, processors, etc have advanced lightyears since then. We're stuck with a 1998 standard though. At least NTSC left some wiggle room, and NTSC was better than could be achived practically in the 50's anyway.
Do any NTSC TVs today even come with full I/Q demod, or NTSC correct phosphors? The former should be a no brainer - it's just another few transistors on a chip. The latter? Aren't there tinted phosphors that can get you there, too? Actually, didn't RCA's colortrak have I/Q, along with some Panasonics? 
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#92
10-20-2005, 12:00 AM
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Actually the FCC almost went with an analog style HDTV system. Something like the Japanese MUSE HD system. Then some company announced that they could do an all digital system with compression that would make an HDTV signal fit in a 6MHz TV channel. The FCC said "Great, do some refinements, field test it and make it good, and we'll do it, an all digital HDTV standard". About the only real arguement was about the transport stream modulation onto the TV channel, 8VSB or COFDM. COFDM is a little better with ghosting, but with its 2000 or 8000 subcarriers, severe clipping in transmitters and intermod in receivers is a big problem. If all 8000 subcarriers decide to turn completely on full ampliitude at the same time, you'd have a huge power spike to try to transmit or receive without overload.
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#93
10-20-2005, 01:21 AM
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With my over the air HDTV reception and quality, the ONLY complaint I have is when networks add those stupid subchannels. It almost exclusively affects 1080i main channels quality, you start to get pixelization, sometimes not even on fast motion. Here in Los Angeles area it's NBC which is 1080i and one stupid weather subchannel. Other night on Conan, they had Dolly Parton on, and just her slightly moving around and her large amount of hair made pixelization around her chin and neck that looked awful. Jeez NBC who were the forerunners of color can't even show someone sitting in a chair talking and no camera movement without it degrading?? Also it may be a problem of them not broadcasting using the full 19mbs or something but I have no idea how to measure it. But they are by far the worst out here. Otherwise CBS, ABC etc look great out here and to me HDTV looks incredible unless they screw it up and don't give a damn like NBC L.A. Really hard to believe the people there just accept this lousy quality, sometimes NTSC would look BETTER! The TWO subchannels have almost no effect on ABC out here which is 720p. CBS is superb, 1080i and no stinking subs. I'm using a 51 inch crt-based projection Hitachi.
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#96
10-20-2005, 02:23 PM
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#97
10-20-2005, 04:05 PM
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#98
10-20-2005, 04:30 PM
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__________________
From Captain Video, 1/4/2007 "It seems that Italian people are very prone to preserve antique stuff."
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#99
10-20-2005, 06:17 PM
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Back in 1988 I won an RCA Dimensia 27" floor model console in a contest (I could never have had to been able to justify buying it as I was in the process of restoring 2! CT-100's at the time, John Folsom now owns one of those 2). The Dimensia had wide I and Q demod on chip! Upon completion of the first CT, I parked it next to the Dimensia with a parallel RF feed. The similarities in the color reproduction was nothing short of amazing. The only plusses to the Dim. other than acreage was overall brightness and HV regulation. Even the signal sens. was comperable. I played that Dimensia brutally until '03 when the crt started to slide! Not too shabby. I still have it in queue waiting for rebuild. One of my all time worst offenders of the faith candidates is the RCA CTC-18x family. I quit counting how many of them I've had to do the tuner ground resolder routine (along with Bad regulator darlingtons, regulator ic's, up in smoke yokes, HOT's, and oh yes, EEproms!) I'll still fish them out of dumpsters, but only if they are near the top with no soured milk or other grossities stuck to them.
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#100
10-20-2005, 06:50 PM
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Oh yeah, I nearly forgot that a friend of mine ( he's still a friend in spite of this) knowing my reluctance to throw away anything tv related, gave me a '67 vintage Motorola 21" rect. tube floor model. Since then I've only seen one other rect. 21" floor model and that was an RCA XL-100 and that was a pretty decent set. This set had a Channel Master CRT in it in good shape and the cabinet was mint. Thats all I have good to say about it as far as my initial assesment goes. Aside from half the tubes in it testing marginal, the horizontal output tube was cracked and the flyback melted (then I got to looking at the Sams for it and noticed their novel 1! tube based color demod circuit and how it resembled the one that was used in the Magnacrap tube chassis - the one with the push pull focus control - and neeeever looked good to me). Anyway, I thought about risking censure by the collecting community and going ahead and making a bookcase or a bonfire out of it. Then it dawned on me, the entire front mask assembly was identical to a TS-919 gen 1 Quasar table top set I had "restored" and was very fond of except for it's scratched up contact paper on steel cabinet. They even both had the tint control (like the maggie chromatune control) and the convergence paanels were in the same place behind the speaker! Needless to say, I have the only floor model 21" Quasar I've ever laid eyeballs on and it is a sweet little set (the ho-made back cover looks a little cheesy but it keeps the cat alive). If anybody has a better use for one of these abomin-ola's, let me know.
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#102
10-21-2005, 06:33 PM
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#103
10-21-2005, 06:51 PM
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Yeah, thats my set. flattest crt I had seen up till that time and a multi-funtion remote that will still control most RCA products(even my Proscan vcr). I did have the typical scan rectifier board solder problems and the ex - XYL snatched ant. 1 coax connector out of the tuner can, but with a little weller and 90/10, I WON! Wow, what a contrast to those mid 90's CTC-18x dumpster dunnage sets , huh?
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#104
10-21-2005, 06:55 PM
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That Dimensia IQ demod design was ingenious in that they found a way to make an I channel delay line with only one IC pin (plus one external transistor). As an analog IC designer, I thought that was one of the neatest tricks I ever saw. Essentially, they tied the input of the delay line to ground, then drove the delay line output and what would normally be the delay line ground up and down with the input "I" baseband voltage. They then used the same driving pin to sense the output current!
Despite my admiration for the IC design, When I tested one of those sets for chroma resolution (working at Zenith), it was essentially no better than the R-Y/B-Y sets. The I channel high frequencies were quite attenuated. It appeared that there was too much phase distortion in the IF to allow the I channel high frequencies to be boosted to a useful level. I went through some effort to design a better IF for a possible wideband design myself, but concluded that the NTSC got away with their system design partly because tests were done on small screens. My basic conclusion was that NTSC needed a more symmetrical Q filter in the transmitter - it should have traps on the upper and lower edge that match the 4.5 MHz sound trap (+/- 900 kHz from the chroma carrier). If the Q sidebands transmitted would be sharply curtailed beyond +/- 500 kHz, there could be no quadrature crosstalk from Q into I, and it would behave like the NTSC intended - but NTSC Q filter specs were too broad, and any reasonable IF would show quadrature distortion and therefore the I response could not be boosted to the theoretical value. I proved this by modifying the filters in an NTSC encoder -and when we saw how well it worked, we gave up trying to design an I/Q set, since there was no way to go back and modify every encoder out there. Last edited by old_tv_nut; 10-21-2005 at 06:58 PM.
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#105
10-21-2005, 08:26 PM
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Gee, it's a shame I don't live near the Illinois area Old Tv nut, I would really love to pick your brain more intensely! An old friend of mine who just recently passed was a long time employee and xmtr super for our local CBS afilliate. When I got eat up with the vintage color bug in the 80's, we talked at lenght about the challenge of getting a color signal through those old RCA 25kw coffee cans and on the air. Seems as though there was an issue with dfferential phase distortion that reeked havoc with satisfactory hue reproduction and that it was more apparent on I/Q sets. BTW, was RCA the only man. to try and reintroduce I/Q demods in the 80's and didn't this coincide with their introduction of real comb filters? Shame they didn't have those in "54. Sorry if I'm off thread topic.
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