Re: CRTs on Ebay


Don Black <donald_black@...>
 

Thanks Craig, interesting comments. Actually I'm in Australia but worked on some C1958 Marconi prototype colour equipment. Very useful experience. The PAL is rock solid by comparison.
Our colour service started in March 1975 using PAL. For a few years before that a few of us were watching some colour programs from tapes from the UK and England. The local signal processors stripped off all the colour burst used to lock the chroma circuits but with PAL you can recover lock signals from the chroma which wasn't filtered out. Philips hawked some prototype sets around the trade in the late sixties (trying to push colour introduction I think) and included a little chroma lock board to allow users to watch the program. It recovered the lock signal and just injected it into the chroma oscillator as a trigger but apart from just managing lock on a stable signal generator I never saw it successfully lock to an off-air program (It might have worked on a properly stabilised program?). I thought it would be better with an AFC phase locked loop and built up a few boards using it. They worked far better than I hoped and would always lock solidly to the weakest chroma. The quality off the tapes varied from excellent to colour snow but it always locked right up. So for a few years we watched just about anything that moved in colour. I've still got a board kicking around somewhere.
I believe when they were developing what became he NTSC colour system in the US it was suggested it would be advantageous to switch one colour signal phase on alternative lines (same as PAL) but it wasn't considered worth it and didn't happen. The one line delay line really makes the PAL system and I guess there wouldn't have been a cheap 64µs delay line available. It was the development of the acoustic glass delay line that really made it viable. The same delay was later used in VCRs for dropout compensation. There is still some advantage of the PAL system without a delay line, the eye averages the colour errors but gives the Venetian blind effect.

Don Black.

On 13-Jan-14 12:36 AM, Craig Sawyers wrote:
 

=====================
Have you ever worked with old NTSC gear Craig. Capable of good results but
Never Twice Same Colour oh so true, especially compared to the stability of
PAL.
Still a great development for its time which served well for over half a
Century.
Don Black.
=====================

No Don - but worked quite a bit in the States at one point, and suffered
NTSC with arbitrary colours in hotel rooms many a time.

That was the big advantage in the UK of being second instead of first in
analogue colour television, and PAL was devised to work around the phase
distortion colour artefacts of NTSC.

There used to be similar acronyms for PAL and SECAM too.

Oh yes here we are (google is your friend)

SECAM - System Essentially Contrary to the American Method
PAL - Perfect At Last

I don't know what digital TV is like in the US, but in the UK the only
complaint is that the audio level varies over very wide limits from channel
to channel. Set it correctly for on channel and you can be near deafened
when swapping to another channel. That was never the case with analogue TV,
which like FM radio had a dynamic range the led to fairly standard audio
levels, with the only exception being adverts which were (and still are)
compressed so that the perceived audio level is louder than the programme.

Craig





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