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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 17th Nov 2008, 3:21 pm   #1
Al (astral highway)
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Default Understanding the 'intelligence' in a video signal

I want to understand the components of a video signal as prep for tackling my first TV restoration sometime soon. It will be a 60s set, b/w.

I am reasonably au fait with UHF construction methods (I've built a VHF+ converter for tiny signals) antennae, the sound receiver, line output (I isolated one as an EHT+ supply when I was 14) and power supply of a TV, but also have big gaps in my knowledge, especially the video amplifier and frame timebase. I do know how scanning works, however.

I know how timebases work in isolation, but not as part of the whole broadcast to picture chain. This is no small 'gap', obviously, when it comes to understanding telly!

When I say 'I want to understand', I mean a really thorough explanation that is in terms of waveforms and their components and any relevant timings. If there are any good online resources, that's brilliant.

Can I give an example of my level of ignorance? Right now, not having made a study of this, I don't know whether the sync pulses are generated within the receiver or are a component of the signal intelligence through the aerial! I guess they come with the signal. But that's just by way of example.

Cheers, experts!
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Old 17th Nov 2008, 3:32 pm   #2
ppppenguin
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Default Re: Understanding the 'intelligence' in a video signal

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Originally Posted by astral highway View Post
.... I don't know whether the sync pulses are generated within the receiver or are a component of the signal intelligence through the aerial! I guess they come with the signal. But that's just by way of example.
Oh what a huge subject! To answer that specific question, sync pulses are sent as part of the transmitted waveform and are used to synchronise the line and frame timebases at the receiver so that they scan at the same rates and phases as at the sending end. The idea of sync pulses was properly worked out in the 1930s by Blumlein and his colleagues at EMI and Kell, Bedford and their colleagues in the US.

Books(all out of print):
Amos and Birkinshaw, Television Engineering vols1-4.
Hutson: Colour Television Theory
Fink: Television Engineering Handbook (various editions)
Wharton & Howarth: Principles of Television Reception
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Old 17th Nov 2008, 3:38 pm   #3
jhalphen
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Default Re: Understanding the 'intelligence' in a video signal

Hello,

interesting reading here:

http://www.sptv.demon.co.uk/

If you give me your Mail address, i can send you TV basics documents scanned from Rohde & Schwarz (test gear manufacturer).
Namely:
- TV Technology (24 pages)
- TV Standards (16 pages)

*if demand is high, i will post to my PhotoBucket site for others to see.

Best Regards

jhalphen
Paris/France
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Old 17th Nov 2008, 3:42 pm   #4
Patrick Dixon
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Default Re: Understanding the 'intelligence' in a video signal

There are line sync pulses at the beginning of each line (in the horizontal blanking period) and a frame sync sequence at the top of each field (in the vertical blanking period). These pulses are below the black level of the video signal.

From these, you can determine black level, and the vertical and horizontal start of line and field. The two fields each contain half the lines and are interlaced to give the complete picture frame.

That's a start anyway ...
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Old 17th Nov 2008, 4:08 pm   #5
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Default Re: Understanding the 'intelligence' in a video signal

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Thanks! I will send you my mail address.
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Old 17th Nov 2008, 4:10 pm   #6
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Default Re: Understanding the 'intelligence' in a video signal

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. The idea of sync pulses was properly worked out in the 1930s by Blumlein and his colleagues at EMI and Kell, Bedford and their colleagues in the US.
Clever guys, Blumlein et al. I know his name from delay lines used in radar?

Thanks for the reading list Jeffrey. I will try to acquire or borrow some of these
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Old 17th Nov 2008, 8:32 pm   #7
dominicbeesley
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Default Re: Understanding the 'intelligence' in a video signal

Hello,

A good book (covers colour as well)

http://books.google.com/books?id=dRG...9HMQ#PPA542,M1

I've not managed to get a paper copy yet though! It's more 625 line but the monochrome info should get you going.

Also an excellent page: http://www.penders.cwc.net/otsyncframe.html and another good one here http://graffiti.virgin.net/ljmayes.mal/var/tvsync.htm

I have to say, if you've got an oscilloscope then hook it up to a video signal (from a video, DVD, Aurora etc) and get the lines locked you'll see quite a bit. What's broadcast is pretty much that but amplitude modulated for B&W.

If you have a 'scope with a z-mod (i.e. brightness) input feed to that too (you may need to amplify a bit), then if you've got a second channel hook up an AF signal generator set it to 25Hz and you've made a telly, not a good one but it'll get you started.

A really good place to start I have to say is playing with NBTV where the video is at audio frequencies, it's a lot easier to get circuitry working at these lower frequencies and you can get a full-blown, low resolution CRT monitor going very quickly. I was always "scared" of TV until I started playing and now realise it actually does make sense! PM me is you're interested...

Scaling things up to "real" TV is simple, but more fiddly as you need a lot more bandwidth and good behaviour over a large frequency range, but if you're into VHF / UHF stuff you'll know more about that than me...

Dom
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Old 17th Nov 2008, 11:14 pm   #8
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Default Re: Understanding the 'intelligence' in a video signal

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A really good place to start I have to say is playing with NBTV where the video is at audio frequencies...
Hi Dom, and thanks for this and the other bits of advice and links. Excellent stuff and I now have a few leads to follow.
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Old 21st Nov 2008, 4:48 pm   #9
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Default Re: Understanding the 'intelligence' in a video signal

Hello Astral Highway,

Just checking, have you received the R&S data i sent you?

Best Regards

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Old 21st Nov 2008, 5:01 pm   #10
Al (astral highway)
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Default Re: Understanding the 'intelligence' in a video signal

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Hello Astral Highway,

Just checking, have you received the R&S data i sent you?

hello, no. I received an email saying that you couldn't send it to the address you tried -- thanks for trying. I will pm you with the email address again.

thanks
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