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Teletext - Teefax

 
mfd70
(@mfd70)
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If anyone is running a teletext TV or a vintage external decoder and a Raspberry Pi you can have something to decode with Teefax. Some software called Vbit 2 generates a teletext signal on the PAL output of the Pi which can be decoded by a suitable receiver. It would be interesting to see if the Tifax XM11 could decode it, I remember that type of decoder stopped working when fastext was introduced.

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 There are a couple of off screen shots, taken on a plasma TV as I don't have anything old with teletext, there is a facebook group which contributes pages so there is plenty to look at, even Bamboozle if you have a decoder with fastext.

Here is a link to the site with the code;

I don't really understand the code but I was able to follow the instructions to make it work.

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Topic starter Posted : 20/01/2021 9:48 pm
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Sundog
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@mfd70 I admit I read the title as TIFAX, the original Texas Instruments decoder with awful performance.

This project is much more exciting! It seems you can also get a header (hat) board to allow insertion of Teletext into your own video feed.

 

Funnily enough my interest is at the other end. I've been contemplating the best way to save Teletext from off-air recordings.

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Posted : 24/11/2021 9:00 pm
Lloyd
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I have had this running too, I think there was a thread about it a few years back on here. I've had it working on an old Rediffusion Mk4, no idea what decoder is in it though!

I have also had some mild success with retrieving old teletext from bog standard VHS tapes, it was a bit garbled, but vaguely legible! I was using a Sony stereo VHS machine, one of the last made, and a Philips LCD TV to decode it.

Regards,

Lloyd

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Posted : 28/11/2021 8:55 pm
Sundog
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@lloyd I'm afraid VHS hasn't got the bandwidth for Teletext, so I don't think its worth putting a lot of effort trying with those recordings. Unfortunately this also means that the vast amount of VHS recordings, the Teletext is probably irretrievable, which is a shame.

The good only news is that SVHS works very well. The slightly increased bandwidth makes Teletext recovery very good - though not perfect. But few people paid the SVHS premium for machines and tapes.

John

 

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Posted : 28/11/2021 10:01 pm
WayneD
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Posted by: @sundog

@lloyd I'm afraid VHS hasn't got the bandwidth for Teletext, so I don't think its worth putting a lot of effort trying with those recordings. Unfortunately this also means that the vast amount of VHS recordings, the Teletext is probably irretrievable, which is a shame.

The good only news is that SVHS works very well. The slightly increased bandwidth makes Teletext recovery very good - though not perfect. But few people paid the SVHS premium for machines and tapes.

John

 

That USED to be the case, but Jason Robertson of The Teletext Archaeologist can recover Teletext data from standard VHS tapes as well as Betamax and even N1500:

https://teletextarchaeologist.org/

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Posted : 28/11/2021 10:10 pm
Sundog
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Well thank you, that's very interesting, I'll follow that up.

Apologies for posting out of date info!

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Posted : 29/11/2021 9:25 am
WayneD
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Posted by: @sundog

Well thank you, that's very interesting, I'll follow that up.

Apologies for posting out of date info!

Hey, don't worry about it. Technically it's not out of date as it's not really possible to load teletext data directly from a standard VHS tape to a TV (although some Hitachi VHS machines seem to be able to do this quite well). 

Technology and general information about stuff is always evolving. 

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Posted : 29/11/2021 6:37 pm
Sundog
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@wayned Well I worked with the early JVC designed filter circuits. These were the ones where the Y filtering was switched to have a wider bandwidth on monochrome than colour. We could retrieve Teletext in the monochrome mode but not colour mode. Later VHS machines had only colour mode as a cost saving and as there were fewer monochrome transmissions.

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Posted : 29/11/2021 6:59 pm
WayneD liked