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  #31  
Old 10-06-2016, 07:30 AM
kf4rca kf4rca is offline
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As I recall, the vir switch had its own set of controls. So, you could make it look like anything you wanted.
Those vir generators are all over Ebay if you wanted to play with one. Except for the VITS100, they also have a full field test generator with a boatload of test signals. The one I liked was the Tektronix 1910.
I've seen them as low as $30.
But I think the vits deleter and inserter section could be used in eradicating copyguard thats in the vertical interval.
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  #32  
Old 10-16-2016, 10:41 PM
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As i recall, it did have internal color and tint adjustments for VIR, and manual adjustments for non Vir mode.. If i remember correctly, it performed well most of the time, but there were times when we had to disable it because it didnt agree with all programs...

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  #33  
Old 09-28-2017, 10:04 AM
kf4rca kf4rca is offline
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Here is the only 19" GE VIR set I've ever seen. I think most people bought the stripped down model despite the massive advertising campaign.
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File Type: jpg GE_VIR_SET_WCBD.jpg (52.4 KB, 32 views)
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  #34  
Old 09-28-2017, 10:19 AM
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A friend of mine owns a VIR set with a gassy CRT.
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  #35  
Old 10-01-2017, 03:42 PM
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I got a VIR-equipped Electrohome console from 1978 just yesterday. It starts but I'm sure it'll need work. Good thing I got the manual, and saw this thread, otherwise I still wouldn't know what it is.
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  #36  
Old 02-20-2018, 02:58 PM
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I think I've solved the problem for RCA's original NTSC spec with a better implementation:
Just have colorburst for almost a whole line period in the last serrated segment of the field sync pulse
at ~50% luminance level(like GE-VIR) (picture level of light complexions.)

This gives nice clean, long duration subcarrier reference every sixtieth of a second (like VIR) (no burst every line needed)(who gives a flip about airplane-flutter.)

Then 1950s era receivers simply run separated vert sync thru a HPF to obtain subcarrier phase reference (no countdown circuit chips required 1970s VIR)
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  #37  
Old 02-20-2018, 03:20 PM
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Quote:
Originally Posted by NewVista View Post
I think I've solved the problem for RCA's original NTSC spec with a better implementation:
Just have colorburst for almost a whole line period in the last serrated segment of the field sync pulse
at ~50% luminance level(like GE-VIR) (picture level of light complexions.)

This gives nice clean, long duration subcarrier reference every sixtieth of a second (like VIR) (no burst every line needed)(who gives a flip about airplane-flutter.)

Then 1950s era receivers simply run separated vert sync thru a HPF to obtain subcarrier phase reference (no countdown circuit chips required 1970s VIR)
Do you mean a different version of NTSC with subcarrier reference only in the vertical segment but not in each line?

1) Does not solve the problem of having it re-inserted in order to meet FCC signal specs. The original problem was in good part due to the locally reconstituted sync and burst having the wrong phase and amplitude compared to what had happened to the chroma coming over the network. Simply passing the degraded burst to the transmitter was a non-starter, as it could cause problems with color killers in receivers.
2) Not possible to use it with affordable crystal oscillator / phase-locked loop technology, since the oscillator in the receiver would need to have a free-running frequency within 30 Hz of correct, or side-lock could occur. With burst on every line, the free running crystal needs only to be within half that, or 7867 Hz. To insure quick lockup, the oscillator actually should be off no more that 10% or so of the nearest sideband and the loop bandwidth should be just wide enough to pass a beat frequency. Remember, horizontal rate sidelock is what was used in gated-rainbow color bar generators. This proposal would allow accidental vertical sidelock, and would require a crystal oven for stability and/or a customer color lock control to prevent it.

A very thorough theoretical study was done of the color burst to verify that once per horizontal was the right way.
http://ieeexplore.ieee.org/document/4051510/
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  #38  
Old 02-24-2018, 01:25 AM
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"Not possible to use it with affordable crystal oscillator"

What if, after transition of H sync to black, the back porch was raised to 50%?

Seems the GE VIR locked nicely to 60hz interval reference with a cheap osc.
I must look up a schematic of a VIR board, haven't searched yet.

As for that paper from IEEE, they want $33 to read it, good luck with that.
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  #39  
Old 02-24-2018, 09:57 AM
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The oscillator in the VIR sets locked to the regular burst as usual. The VIR made a secondary adjustment of phase. The goal of the VIR was to provide a secondary signal that suffered all the phase and amplitude perturbations as the video chrominance, all the way from the original encoding at the studio. VIR and the burst would always have the same frequency, since the local proc amp sync and burst reinsertion was locked to the incoming signal from the network. VIR was never intended to be a frequency reference.

Later, when the use of frame synchronizers became common, even the local frequency could be different from the incoming. VIR could no longer be carried all the way through the chain.
[Edit - maybe it could be - have to think about that]

For another thing, some stations began using local VIR insertion to adjust transmitters in an automatic closed-loop system, and this broke the chain as well.

Before frame synchronizers, the major networks had established atomic clock references to which everything was synced. These were so stable that you could sync a receiver to one network it displayed the picture from another (which I actually did for an experiment when I worked at Zenith). The National Bureau of Standards published a paper on using the network color burst as a better frequency reference than WWV.

As far as putting the burst on a pedestal:
1) The reason for the pedestal in VIR is so that any differential phase incurred along the chain would be compensated precisely nearer to skin tone luminance.
2) The reason for not putting the burst on a pedestal in the original NTSC/FCC specs was to prevent making it visible during retrace in sets that didn't have power retrace blanking. There was a proposal to put it on a pedestal to avoid possibly clipping it in studio amplifiers or transmitters, but this was rejected. Adding the pedestal after the standard was established would have required expensive surveying of the existing receiver population to make sure retrace was no longer a problem.
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Last edited by old_tv_nut; 02-24-2018 at 10:13 AM.
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  #40  
Old 02-24-2018, 11:39 PM
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Mr WB, given the alleged advantages of PAL, (as well as its technical drawbacks)(and inconvenience of broadcast & consumer media playback incompatibility), do you think it was wise for those few South American countries to adopt (525/60) PAL-M & PAL-N?
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  #41  
Old 02-25-2018, 03:48 AM
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Brazil certainly decided to play "odd man out" with PAL M. I can't see any real reason why they shouldn't have used NTSC. They were the only 525/60 country that didn't use NTSC.

PAL N is another matter. Argentina had the unfortunate combination of 625/50 monochrome TV with US channel spacing. So they couldn't use standard NTSC or standard PAL. Something had to give and the result was that ugly kludge of PAL N.

The arguments for PAL vs NTSC have been gone over many times. When Europe was looking at colour systems they could have adopted NTSC, suitably adapted to 625/50. The BBC and others experimented with 625 line NTSC (and 405 line NTSC) in the 1950s. Rightly or wrongly, at the time, the colour phase accuracy problems in NTSC were seen as severe. Hence both PAL and SECAM. In the later days of NTSC improved technology meant that NTSC could overcome the phase and differential phase problems.

Later still it was found that PAL was harder than NTSC to accurately convert to colour components for the digital world. Again advances in technology have made this unimportant.
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  #42  
Old 02-25-2018, 09:49 AM
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Quote:
Originally Posted by NewVista View Post
Mr WB, given the alleged advantages of PAL, (as well as its technical drawbacks)(and inconvenience of broadcast & consumer media playback incompatibility), do you think it was wise for those few South American countries to adopt (525/60) PAL-M & PAL-N?
I think the main disadvantages of adopting PAL in South America were economical, that it made it less likely that a color TV manufacturing plant could be established there without government support either directly to the manufacturer or by high tariffs on imports. Plus, the production and stocking of special models for those countries may have raised retail prices.

Technically, once equipment became transistorized and stable, the only advantage of PAL transmission I can think of was the reduction of wrong hues in ghost images.

There may have been an improvement in color accuracy (as there was in Europe) if the cameras were matrixed to the EBU phosphor standards and receivers used unmodified R-Y and B-Y axes. In the US, color matrixing was a sort of wild west situation in which CRTs did not use NTSC phosphors, but cameras (at least the early ones) were designed for them, while different TV makers did various non-ideal modifications to the chroma decoders to compensate approximately.
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  #43  
Old 02-25-2018, 09:54 AM
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As a side note, I met someone from Argentina who said that many there learned to understand Portuguese because Brazil had the best soap operas.
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  #44  
Old 02-25-2018, 11:21 AM
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A late friend of mine who'd lived & worked in the TV/radio trade in Argentina sang the praises of system PAL N. He said if you put an average British PAL I & an Average Argentine PAL N set side by side you wouldn't be able tell the difference between them. He said Britain chose the wrong 625 system & should have gone for system N.

Must admit I was impressed with the NTSC M pictures I saw when I was in USA & Bahamas..
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  #45  
Old 02-25-2018, 11:18 PM
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Some SA countries appeared to have been spooked by Euro trade delegations - they paid a hell of a price. Not as easy to bamboozle: Korea, Taiwan..
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