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Old 29th Nov 2016, 12:41 am   #1
Terry_VK5TM
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Default BBC TV - The beginning

Apologies if this has been posted elsewhere here.

A lot of content and early recordings from the beginning of the BBC.
Some early TV receivers on the Sets and Signals page.

http://www.bbc.co.uk/historyofthebbc/birth-of-tv/

Terry
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Old 29th Nov 2016, 2:30 pm   #2
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Default Re: BBC TV - The beginning

Thanks for the link, Terry. I must say I've never come across this particular site before. I note that once again we get the quote that "‘Cuts’ from one camera to another were not yet possible - only slow ‘fades’ lasting at least eight seconds". I've heard this many times over the years, but never an explanation as to why it was so. Does anyone know?
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Old 29th Nov 2016, 3:30 pm   #3
fetteler
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Default Re: BBC TV - The beginning

Persistence of the display??
Speed of switches?
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Old 29th Nov 2016, 5:07 pm   #4
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Default Re: BBC TV - The beginning

I wonder whether the sync between sources was weak, or even non-existent.

ISTR that a frame roll was common when the programme did switch between different origination sources.

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Old 29th Nov 2016, 6:10 pm   #5
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Default Re: BBC TV - The beginning

Surely all the cameras in one studio were synced? It'd be mad not to!
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Old 29th Nov 2016, 6:18 pm   #6
fetteler
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Default Re: BBC TV - The beginning

Err... and it would certainly not be possible to mix between non sync sources... but I wonder if I have misunderstood the goings on - are we talking about a fade to black, a nonsync cut and then fade up the next shot? Gives a black frame roll which might have been the best of a bad job.
Having trouble understanding why the cameras wouldn't be synced though. I mean, the system sort of relies on it.

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Old 29th Nov 2016, 8:06 pm   #7
bluepilot
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Default Re: BBC TV - The beginning

Quote:
Originally Posted by Hartley118 View Post
I wonder whether the sync between sources was weak, or even non-existent.

ISTR that a frame roll was common when the programme did switch between different origination sources.
Did the BBC have AC mains or did they still have DC mains in the 1930s? With DC, presumably every camera would have generated its own scanning frequencies. The fade was "at least" eight seconds. What takes eight seconds that wouldn't work with say seven and a half?

I remember when I was a boy we often had bars going up or down the picture where presumably the BBC's mains wasn't synchronised with ours and change of source could cause frame roll until everything got synced again.
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Old 29th Nov 2016, 8:54 pm   #8
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Default Re: BBC TV - The beginning

For what it's worth, I've never been convinced by this story - at least as applied to the Marconi-EMI iconoscope cameras as it was a fully synchronised (actually 'driven') system with full video clamping ('DC working') through to the transmitter. Nothing should really have upset the vision chain very much in the way of mixes and even cuts.

Now, in the case of the Baird television Ltd (BTL) system, they had the IFT camera, a telecine, a flying spot camera and potentially a Farnsworth Image Dissector camera. A sudden cut or rapid fade between any of these sources could violently upset the average DC level (Average Picture Level). This would have resulted (potentially) in a massive power change in the un-clamped ac-coupled video of the BTL modulator. Thus, it is my supposition that only a slow fade would be permitted on the BTL system to prevent transient surges in the Metropolitan Vickers vision transmitter.

The Marconi-EMI transmitter, with its patented clamped 'DC working', would be immune to this problem but the story has persisted down the ages and has been falsely applied to the Marconi-EMI system.

I would love to hear an alternative explanation, but I'm sticking to my theory until something better comes along!

Best regards,

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Old 29th Nov 2016, 9:03 pm   #9
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Default Re: BBC TV - The beginning

Spinning disks generate their own syncs. electronic telly needs them from somewhere. They may as well be a central position and sent to each camera/telecine via two bits of cheap cable. Saves a lot of room and complexity at the camera end too.

Same as PaulM but from a different angle.
 
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