SECAM anyone?

[ceebee23]

I think all of us are familiar with NTSC and many of us are also familiar with PAL colour standards....but there is another major broadcast standard out there ....and it is rarely mentioned ....SECAM.

I know very little about it in practice ....although I have read technical articles I have never spoken with anyone with any practical experience of the system. It is as I understand it a form of line sequential colour system.

Given that it is in use in France and Russia and elsewhere there must be someone out there who has come across it in use!

Of course a quick study of DVDs coming from france is instructive ....they are all produced in PAL!

chris

[domfjbrown]

I *think* PAL/SECAM are compatible - not sure what the difference is, as I think the frame rate/lines are the same. Certainly our blank VHS tapes in the UK used to (maybe they still do) state "PAL/SECAM" on them.

[ceebee23]

Indeed ...the 625 line / 50 field standard is used in most PAL and SECAM countries which means that at least the monochrome standards are compatible ...the difference is in the colour system ...with SECAM, I understand, the colour information is sent line by line with a delay line built into the receiver so that the colour information is never simultaneouly present in the signal.

The main problem seems to be to identify what is a red or blue line in the signal and this is done in a number of different ways depending on the version of SECAM employed.

[kc8adu]

since when does a blank tape care what tv standard you record on it

Originally posted by domfjbrown
I *think* PAL/SECAM are compatible - not sure what the difference is, as I think the frame rate/lines are the same. Certainly our blank VHS tapes in the UK used to (maybe they still do) state "PAL/SECAM" on them.

[domfjbrown]

Originally posted by kc8adu
since when does a blank tape care what tv standard you record on it

No idea - it's probably down to running time, since NTSC VHS runs the tape faster than PAL.

[Sandy G]

Here's a little more info on SECAM, courtesy of that "Behind the Tube" book-. Sez SECAM was proposed by the French partly out of chauvinism-imagine that- & partly to minimise color errors produced by inferior intrcity microwave transmission & eaely VTRs. As those systems have improved, SECAM's "advantages" have become irrelevant, & it does have some disadvantages. SECAM receivers are more complex, it's not easy to convert to PAL or NTSC, doesn't lend itself to special effects such as fades or lap dissolves. Finally, in the absence of signal distortions, it doesn't have the picture quality of NTSC or PAL. Ze French strike again...-Sandy G.

[House de Kris]

Back when I was working on a video tester, our goal was to support all standards. Yes, the SECAM standard is pretty strange. Few people know this, but the derivation of the SECAM name came from: Specifically Engineered Contrary to the American Method. In the end, there wasn't enough of a market of SECAM chips to warrent us making our tester compatible with SECAM.

The main thing about SECAM is that not enough information is supplied on each line for full color information. As I recall, the color information alternated per line. For example, one line has the green-red info, followed by green-blue, followed by green-red again, and so on. Now that I read that explanation, I think my memory from a project nearly 20 years ago is faulty.

More complicated with poorer performance (and reliability)? You sure the French didn't hire some British engineers? LOL Sure sounds like one of their cars.....come to think of it, sounds just like a French car too!

How the hell Europe stayed mobile for so many years boggles the mind. There's a saying in the old car crowd, the Brits worked on their cars all week so that they could drive them on the weekend, while Americans worked on them on the weekend so they could drive them all week!

Anthony

[Sandy G]

Yeah, sez here La Belle France was only able to browbeat the Russians & the Comecon countries, besides France themselves, into adopting SECAM. About everybody else went for Pal or NTSC. Way to go, jerkwads !! I'm sure ALL the big French electronics companies were working overtime for years turning out SECAM color sets for the ZILLIONS of affluent consumers in Romania, the DDR, Poland, Mother Russia...By God, we've got ze feelthy Americans on ze run this time, Pierre! Yes, Jacques, an' when ze Concorde comes on line in a few years, we gonna rule ze skies, too ! Boeing an' Mc Donnell-Douglas better watch out !-Fictitious French conversation about 1968...HehHehHeh...-Sandy G.

[ceebee23]

actually SECAM was designed like PAL to overcome the inherent phase problems of NTSC .....although the one technician I know who worked with SECAM (in France in the late 60s) said to me that in poor reception areas there were problems because the sets had problems identifying whether they were receiving a red or blue line...and the sets had no manual control to fix it!

But then early PAL sets suffered dreadfully from "Hanover Blinds" ....alternating bands of green and red as the set tried to sort out which line was in phase and which line was 180 degrees out of phase! (A problem only resolved by the use of a delay line in receivers...ironic because this was one of the reasons SECAM sets were more expensive ..which was one of the reasons PAL was selected in Britiain).

But I also know that the choice between the german developed PAL and French SECAM for Britain was a close run thing.

...of course I imagine chroma key etc would be a problem for CBS field sequential as well as SECAM ....

[andy]

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[wa2ise]

SOme years ago I and another engineer had to design a digital chip to demodulate NTSC, PAL and SECAM. It's now the Samsung KSO127 if I recall correctly.

SECAM uses FM to modulate its color subcarrier. U is sent on one line, then V on the next, alternating. The receiver knows which is U and V as the frequency of the subcarrier is different for U and for
V. But unlike NTSC and PAL, the subcarrier amplude is constant, even in colorless areas of the picture. Not quite, they did another trick of reducing the amplitude at and near the subcarrier frequency, and letting it be higher for the higher sidebands. About 10 or so dB down at the subcarrier. Go any further and the FM demodulator loses it and you'd get noise. SO you always have cross chroma in the luma. Also any high frequency energy in the luma that happens to be near the chroma carrier can "capture" the FM demodulator and you get fake colors. There's also preemphasis of the U and V information at the encoder at the TV station and the demodulator needs to do deemphasis (cuts noise some, just like FM broadcast radio audio).

You can't separate the luma and chroma carriers too well. About the only thing you can do is notch out the spectrum around the chroma subcarriers. Comb filters wont work as the line to line correlation of NTSC and PAL isn't there.

[nasadowsk]

Why did PAL take so long, anyway? Unless I'm missing something, save for the frame/line rates and the phase flip thing, isn't it just mostly a rip off of NTSC?

[andy]

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[domfjbrown]

Originally posted by andy
I think it was mostly a case of the bureaucracy taking a long time to pick a standard.

That'll be the British way - too much red tape and wasted money. Tony Tit Blair is planning to axe a rather large amount of civil servants soon - and I can bet it WON'T be the inaffective middle management that goes - you know, those muppets that have brought our NHS to its knees...

As for British cars - we don't have many - they're either all GM, BMW or VW I think there's only Morgan and TVR left now and I bet they're owned by the Japanese...

At least we can't lay claim to Citroen (ha ha ha!!!) or FIAT (Found in a tip). Or for that matter Ford (Fix or repair daily/found often at roadside dead). On that note though, I wish they'd bring back a 35 anniversary replica of the Mk1 UK Ford Capri - medallion man car yes, but there's something about it!