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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 1st Apr 2010, 3:39 pm   #21
practical
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Default Re: "SECAM has 819 lines"

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Originally Posted by cheerfulcharlie View Post
The SCART plug was developed because of something to do with SECAM causing streaky lines on captions IIRC -but maybe wrong.
That rings a bell. I believe the problem is that if a VCR or a set-top box uses a character generator to insert text on top of SECAM-encoded video, it causes horizontal lines to the right of the inserted text. I remember seeing an example of this. This must have given the French a strong incentive to develop the RGB-based Peritel connection, aka SCART.
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Old 1st Apr 2010, 4:14 pm   #22
brianc
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Default Re: "SECAM has 819 lines"

So we can thank the French for giving us, albeit in a roundabout way, decent pictures without the coding footprint by forcing manufacturers to produce component video from AV accessories. Good on yer.
Cheers
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Old 1st Apr 2010, 4:36 pm   #23
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Default Re: "SECAM has 819 lines"

I think the French also led the way with component working in studios too. For much the same reasons. You can't fade or mix SECAM without doing horrible things to the picture quality and the only other alternative was to do all the studio stuff in PAL, then transcode to SECAM for transmission.
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Old 2nd Apr 2010, 3:53 am   #24
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Default Re: "SECAM has 819 lines"

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Originally Posted by ENGLISH VICTOR View Post
I have grave doubts whether a suitable shadowmask tube would have been available to display secam at it's theoretical best on the 819 line system, at least not for public use at an affordable price back in the 1960s. Equal vertical and horizontal resolution being the name of the game would make 625 lines an obvious choice. I conjecture that the 819 line system was the result of misguided national pride.Whilst visiting France (quite often) in the 60s I dont think I ever saw a domestic set with the full 10.5 MHz. video bandwidth.
I suspect that there was a strong element of national pride involved. In the late 1940s and early 1950s, television would have been very visible evidence (yes) of a country’s technological progress and prowess. So the 819-line system would have been something of a flagship. The alternative for France, assuming that something better then the 441-line system was desired, would likely have been the 625-line system, developed largely in Germany, I think, and anyway derived essentially from the American 525 line system. And though even then Monett & co. were working hard behind the scenes to integrate the French and German coal and steel industries as the first step on the road to the EU, adopting a German-developed television standard might have been thought to be a step too far in the public arena at the time. That is speculation, but it seems evident that “politics” did play a part in the multiplicity of European television transmission systems.

The SECAM system itself has also been described as a product of national pride. Perhaps that is a little unfair, as its origin seems to have had a reasonable technical basis at the time. On the other hand, the persistence with the SECAM system once PAL was developed, but before any regular French colour broadcasting commenced, might have had something to do with national pride.

None of the literature to which I have easy access makes any mention of an 819-line version of SECAM. In fact Jackson and Townsend state: “The SECAM system, invented by Henri de France, was developed in Europe for 625/50 scanning, like PAL, as a means of overcoming the susceptibility of the NTSC system to differential phase distortion.” And then: “Early versions of SECAM used amplitude modulation in common with PAL and NTSC, but this proved unsatisfactory.”

Evidently the original SECAM reference, which I have not seen, is “Le système de télévision en couleurs sequential simultané”, by H. de France, in “L’Onde Electricité”, Volume 38, 1958. This would probably answer a lot of questions, including what colour work was done with 819 lines.

In looking for SECAM 819 line references, I also came across some other comments by Carnt and Townsend (Volume 2, 1969) in respect of French dual-standard colour receiver practice. On IF bandwidth, it is stated: “Cheaper receivers use the same narrow-band I.F. for both standards, but the better models use a 9 MHz I.F. with a narrow-band filter after the U.H.F. tuner.” I seem to recall reading elsewhere that 9 MHz was about as good as it got for monochrome 819-line receivers. In the same section, C&T also comment: “Most colour tubes use dot structures which were originally designed for minimum moiré patterns on 525-line transmissions, but operation on [monochrome] 819 lines is normally acceptable unless there is a considerable amount of high-video frequency detail in the picture. Moiré patterns are more noticeable on 625-line transmissions”. One is left to infer that shadow-mask tubes optimized for 819 lines might not have existed. As a sidebar question, were later colour tubes, such as the Mullard 20AX series, optimized for 625-lines?

Cheers,
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Old 3rd Apr 2010, 3:45 am   #25
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Default Re: "SECAM has 819 lines"

On this page, about halfway down, is a picture of what SECAM looks like with inlaid text:

http://www.pembers.freeserve.co.uk/W...Standards.html
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