Teletext is still somewhat popular here in Austria. Mostly for news, weather, and lottery results. I never got the point, but my parents are hooked since the nineties.
The vertical blanking interval gets quite a rough treatment. You canât rely on anything being there to make it to the tape, but it still has a decent chance. The Macrovision âDRMâ for videotapes used alternating high and low intensity signal there to confuse the VCRsâ input amplifier into forcing a flicker into the recording; that could be stripped with âvideo stabilizerâ gadgets. I almost built one for the fun of it when I was putzing with keying text into image with a microcontroller.
That assumes a good quality of the signal. With lousy signal on a degraded tape, more advanced signal processing methods are likely to be required.
These days, the wiring for the digitizing is much easier than the wiring for the signal decoding in hardware. Then you just have to sit down and fiddle with DSP in silico instead of having to putz around with the decoding hardware.
When I was a kid at high school I attempted to build a teletext receiver/decoder. Failed miserably but it almost worked.
There was a semi-similar service in the states for a little bit in the later half of the 90s. I canât for the life of me remember the name. If you bought a WinTV card in 1998ish, it had software with it that would not only tune and let you view the channels⌠but there was a software that would receive HTML content from select channels. I think WISHTV8 in Indy used it and so did our local PBS station. You could view it in a browser, and typically it was very slow and fairly limited. I think I recall viewing several weather maps that way though.
I just canât remember the name of it, I think it started with the letter âIâ though.
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Aphex Twin was doing that 20 years ago.
Richard D James Album: Corn Mouth contains the loading noise from the attribute block of the loading screen from Sabre Wulf by Ultimate. A short tone can be heard after the attribute block. Matt Westcott suggests that this tone was generated by Keysoftâs tape copying program, The Key, in which case the game was a pirated copy!
Richard D James Album: Peek 824545201 starts with loading noise that seems to be a Speedlock-protected header block from Starstrike 3D by Realtime Software. (The filename bytes spell STARSTRIKE RND, but Iâm not aware of any version of the game thatâs protected with Speedlock.) There is further loading noise throughout the track , presumably from the same source. PEEK is a Spectrum BASIC keyword that retrieves a byte from memory, but the number in the title is not a valid memory address.
Star Trek as well. And the data even got decoded. By software. In 1989.
Money quote:
[Bob] didnât own his own Cray 2 of course, this particular computer was property of the National Security Agency (NSA). He received permission to test Frequency Shift Keyed (FSK) decoder algorithms. Can you guess what his test dataset was?
Try some signals from here:
http://www.sigidwiki.com/wiki/Database
The FSK ones are the best. Try some with slower symbol rate and limited number of symbols; they can be surprisingly melodic. E.g. the CCIR Selcall or CCITT. Or the CIS 20-MFSK XPA, that one sounds like the soundtrack to old C64 BoulderDash game. Or Contestia. Or DominoEX/DominoF. Or generally anything that has the waterfall plot looking like a punchcard.
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Oh my god, I found it! https://en.wikipedia.org/wiki/Intercast
Intercast.
They would send HTML pages, along with things like graphics in the vertical blanking interval of a tv signal. According to that wikipedia page they could also send software. I never saw that though. The program used for it didnât exactly give you much idea of what it was doing. Sometimes the pages it said it had were there, sometimes they werenât.
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