NBTV signal waveform

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NBTV signal waveform

Postby sv3ora » Fri Mar 26, 2021 4:47 am

Hi all,
I want to build and share my own televisor circuit, but I want to ask a few things.

What is the most widely accepted format today (32 lines by...? or...?)

It is not clear to me how the NBTV signal waveform is constructed.
I understand that each frame is constructed from 32 vertical lines (in case of the 32 lines format).
Is there any line sync and frame sync pulses and what are these? (negative, positive, levels?, at the start or at the end of the line/frame?)

I need to know these things before I build and share with you my interesting televisor (It will use a totally different display system).

By the way, please inform me if there is such a circuit built from discrete components (not ICs)

Thank you
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Re: NBTV signal waveform

Postby sv3ora » Fri Mar 26, 2021 6:29 am

I had the beliefe that there was no sync in the 32 lines nbtv signal.
And a televisor could be made using a simple circuit like this https://www.youtube.com/watch?v=_OvHx-Q3mJQ
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Re: NBTV signal waveform

Postby smeezekitty » Fri Mar 26, 2021 7:42 am

The NBTVA 32 line standard is undoubtedly the most commonly used.
http://www.nbtv.wyenet.co.uk/standards.htm
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Re: NBTV signal waveform

Postby sv3ora » Fri Mar 26, 2021 8:20 am

smeezekitty wrote:The NBTVA 32 line standard is undoubtedly the most commonly used.
http://www.nbtv.wyenet.co.uk/standards.htm

Thank you very much, this page explains everything, I'll go for the club standard.

I have found this little circuit http://www.hawestv.com/mtv_schematic/si ... lestTV.htm and I think that this will work as long as the speed of the motor can be controlled precisely. So I wonder, why is the line sync so important? If you have a variable motor speed that stays put, you could ignore the sync pulses and just feed in the NBTV signal to the light source.
I might be missing something though.
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Re: NBTV signal waveform

Postby smeezekitty » Fri Mar 26, 2021 8:41 am

sv3ora wrote:
smeezekitty wrote:The NBTVA 32 line standard is undoubtedly the most commonly used.
http://www.nbtv.wyenet.co.uk/standards.htm

Thank you very much, this page explains everything, I'll go for the club standard.

I have found this little circuit http://www.hawestv.com/mtv_schematic/si ... lestTV.htm and I think that this will work as long as the speed of the motor can be controlled precisely. So I wonder, why is the line sync so important? If you have a variable motor speed that stays put, you could ignore the sync pulses and just feed in the NBTV signal to the light source.
I might be missing something though.

Its a lot harder to get the motor speed exactly steady than you might think. And even the tiniest error in speed means there is a phase drift and the picture rolls.
With that said, I do think line syncs were unnecessary and syncing the disc once per frame is sufficient.
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Re: NBTV signal waveform

Postby Steve Anderson » Fri Mar 26, 2021 1:24 pm

smeezekitty wrote:With that said, I do think line syncs were unnecessary and syncing the disc once per frame is sufficient.

Now there's a challenge! If it weren't for the fact I'm up to my neck in other things I might have a go at it. It's easy for an electronic display, I did it some years ago for 32, 48 and 72-line CRT-based systems. It's probably here on the forum - somewhere!

But with a mechanical display? I used the word 'challenge' with good reason! Not impossible, a challenge...

...not forgetting the source of signal may have its own irregularities if mechanical...

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Re: NBTV signal waveform

Postby M3DVQ » Sun Mar 28, 2021 1:06 pm

I would tend to agree that line sync is irrelevant in a mechanical system, as every line is dependent on the others. That is to say having a separate sync doesn't help you when you have to wait for a hole to come by at its own pace. :D
The sync pulses themselves are useful though, for DC restoration and so on.
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Re: NBTV signal waveform

Postby Steve Anderson » Sun Mar 28, 2021 7:24 pm

M3DVQ wrote:...The sync pulses themselves are useful though, for DC restoration and so on.

Yes, good point...

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