International TV Standards Conference 1949

[ppppenguin]

In 1949 the CCIR held a conference about different standards in TV. This report appears in Proc IRE February 1950. Note how Britain and France insist on going their own ways.

[Mike Watterson]

Pretty much what you'd expect regarding USA, France and UK. At least UK switched to 4:3!
Very interesting.

Was the later proliferation of Secam versions largely political or an attempt to "fix" it? The basic idea doesn't seem too mad an alternative to NTSC (which has a fatal flaw fixed by PAL), but an FM subcarrier for colour seemed crazy.

While "interlace" created problems for film to 30 fps (Simply play 24 at 25 elsewhere) and now is horrible for upscaling, it was a practically "free" method of doing 2:1 bandwidth compression. We are more sensitive to detail in a static or slowly moving scene than rapid movement. Hence no-one objected to interlace. Later DVDs from film for USA stored progressive 24 fps and the player did the 3:2 pull down, hence early enthusiasm for "progressive" and component video in USA, which was nearly pointless in 25 fps countries, especially with RGB SCART. So Component later did HD and AFAIK SCART RGB never supported HD (though it could have, see VGA of 1600x1200 and higher). Also USA has/had a non-interlaced "so called" HD digital mode which is only 480p!

[colly0410]

Interesting that they considered intercarrier sound on a positive modulation system. As far as I know no British 405 line TV's had intercarrier sound, although I've read somewhere that some French system L positive modulation TV's did, can't remember where I read this though...

[colly0410]

Also that two countries favoured vertical rather than horizontal aerial polarisation, I know us in UK were one but who was the other? BTW very interesting read, thanks for posting Mr P
...

[ppppenguin]

The FM colour subcarrier in SECAM meant it was immune to differential phase and gain errors in the distribution chain. It could also be recorded on 2" quad VTRs without any extra kit for colour. In the studio it was horrible. Couldn't directly be mixed or faded.

Intercarrier sound reception on System A (405) would have been more or less impossible. There was no guarantee on sync tip carrier level. It might go to zero, or might not.

[peter scott]

It's interesting that France supported the UK for 405 positive mod in Band I.

Peter

[Mike Watterson]

I think France eventually used PAL in studios/production and converted to Secam for transmission.

[ppppenguin]

The UK suffered from being pioneers. After WW2 nobody would have started a TV service on 405 but we were already there. Much ink has been spilled over whether we should have restarted on 625 after WW2. Lots of arguments for and against but I think the consensus is that there was a political imperative to restart the service ASAP and that meant 405. Remember the UK was stony broke back then and we also wanted the lowest cost option. Could we have televised the 1948 "austerity" Olympics at all if we'd moved to 625?

[ppppenguin]

Another problem for PAL is that the decoder needs a very precise one line delay. Accurate and stable to a small fraction of a cycle of subcarrier. You can receive PAL without a delay line (PAL-S) but it can introduce visible "venetian blind" effects on less than perfect signals. The SECAM one line delay needed only about 50ns accuracy and stability. This could be done with a steel rod rather than a quartz block.

[Richard_FM]

The FM colour subcarrier in SECAM meant it was immune to differential phase and gain errors in the distribution chain. It could also be recorded on 2" quad VTRs without any extra kit for colour. In the studio it was horrible. Couldn't directly be mixed or faded.

I heard SECAM studios used to use PAL or later component mixers & faders, with the output only converted to SECAM late in the chain.

The cost of this kind of setup was one of the reasons the Eastern European countries switched to PAL in the 1990s.