Flipped RGB colours in a TV

[Algr]

They are still proud to announce that Cuba was the second country to have a colour TV broadcast system.

That is ironic! The Castro regime both shut down the color broadcasts, and drove out the people who had set them up.

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Inverted colors is an easy flaw in NTSC, because the hue is determined by measuring the phase relationship between a wave off screen (in the sync pulse), and another on screen (hidden in the signal). If they are in phase, that is supposed to be red. 120° out of phase would be green, and 240° would be green.

But if you need to synchronize multiple NTSC broadcasts together, as you might in a cable TV arrangements, just a few feet of cable at the broadcast station can delay one NTSC signal so that it misaligns with the sync pulse generated elsewhere. (Perhaps in the hotel.) Sometimes at video studios, you'd see huge coils of cable laying on the floor that are just there to delay the signal slightly less than 360°, so that it would sync with something it was supposed to be mixed with! It was a pain, and lots of people didn't understand it, and did it wrong.

 

[sophiecentaur]

the hue is determined by measuring the phase relationship between a wave off screen (in the sync pulse), and another on screen (hidden in the signal

It's not really like that. The colour burst signal is the reference for the phase (and amplitude, btw) of the solour subcarrier in that line - it's all within the signal from each source. The timing equalisation you refer to is necessary because the colour burst on all incoming signals needs to be synced. Without this equalisation, each switch between sources would involve a period where the subcarrier generator drifted into a new phase relationship.

Sometimes at video studios, you'd see huge coils of cable laying on the floor that are just there to delay the signal slightly less than 360°, so that it would sync with something it was supposed to be mixed with! It was a pain, and lots of people didn't understand it, and did it wrong.

BBC Television Centre (London) was built in a circle with studios all placed at equal distances from the switching equipment at the hub so that they could between sources and still keep sync. (Shorter lengths of equalising cable needed for each camera).

In the old days of the UK independent TV service, there was no sync between the regions at all (just the mains 50Hz). Every commercial break had that annoying 'exploding white star' to mask the change in (coarse) timing.

It became relatively easy to re-code colour TV signals when they passed through a common point so switching between sources could be done seamlessly. But CATV systems have often been done as cheaply as possible, squeezing multiple channels into a very narrow space. Without tight regulations, picture quality suffers yet the consumer is happy to suffer that in order to see a 'coloured' picture.

 

[pbuk]

BBC Television Centre (London) was built in a circle with studios all placed at equal distances from the switching equipment at the hub so that they could between sources and still keep sync. (Shorter lengths of equalising cable needed for each camera).

I am not sure that is correct, do you have any source for that (other than the spurious information on Wikipedia, which I have removed)?

 

[sophiecentaur]

I am not sure that is correct, do you have any source for that

OH ye of little faith. I have been in the basement of TC (years ago) when I worked there. (Good enough for you??? ) Here is some evidence for the basement under the fountain.

The architects made a virtue of necessity and put a visible statue at the centre to make it all look nice.

PS I will accept a bouquet as an apology for your ever doubting me.

 

[pbuk]

PS I will accept a bouquet as an apology for your ever doubting me.

Oh there is no doubt about the basement under the fountain (later replaced by the statue), and the video recording suite being located there.

However the Central Apparatus Room was on the second floor of the 'central wedge' of the doughnut: are you saying that cables from studios 3 and 4 (adjacent to the central wedge) were routed out into the centre under the fountain and then back in via the video recording suite and up to the CAR (presumably also with a feed from the CAR back to the recording suite)? Or was the editing and switching actually done in the tele-recording suite?

This drawing may help jog your memory (although I believe this is as designed not as built):
http://www.r-type.org/timeline/time145d.jpg

 

[pbuk]

And was switching between studios preserving frame sync really ever done?
How were the signals generated by the cameras in different studios synced in the first place?

 

[sophiecentaur]

However the Central Apparatus Room was on the second floor of the 'central wedge'

Does that mean that the cables were not originally routed via the hub? I can't find hard evidence either way about what equipment was actually there. I will ask around.

 

[pbuk]

I have found a document that answers all these questions about Television Centre and more: http://www.tech-ops.co.uk/tech_guide.pdf (sorry about the hijack).

In summary:

• There was indeed a central sync generator in the CAR which was fed to each studio.
• Feeds from each studio went to the CAR where switching was performed and fed to the broadcast system.
• There were separate feeds from each studio to the tele-recording suite under the central hub.

Also from http://tech-ops.co.uk/next/wp-content/uploads/2018/09/IEE-BBCTVC-and-Its-Technical-Facilities.pdf (what a mine of interesting stuff!)

 

[sophiecentaur]

I have found a document that answers all these questions about Television Centre and more: http://www.tech-ops.co.uk/tech_guide.pdf (sorry about the hijack).

In summary:

• There was indeed a central sync generator in the CAR which was fed to each studio.
• Feeds from each studio went to the CAR where switching was performed and fed to the broadcast system.
• There were separate feeds from each studio to the tele-recording suite under the central hub.

Also from http://tech-ops.co.uk/next/wp-content/uploads/2018/09/IEE-BBCTVC-and-Its-Technical-Facilities.pdf (what a mine of interesting stuff!)
View attachment 345753

Excellent sleuthing, young man. So now we are up to date with the history of TC. Doing it 'that way round' makes a lot of sense . Everything was analogue in those days and long video delays were a lot of trouble so at least starting with good timing at each source was handy. I wonder how that layout design was arrived at (i.e. technical input). The result was a pretty iconic building which is identifiable from the air.