[abirkill]

This is not a dissimilar system to Teletext[1], which transmitted data in the blanking interval of a broadcast TV signal, and could be interpreted by a TV or other hardware with appropriate support. Teletext was pretty widespread throughout Europe in the 1980s and 1990s.

It was typically used to transmit pages of information (news, weather, etc.) that could be viewed directly on the TV, but the BBC's Ceefax[2] Teletext service was also used to distribute software to the BBC Micro, when equipped with the appropriate Teletext Adapter[3].

In a similar fashion to the Sega Channel system, the Teletext system would broadcast looped data, with popular pages (such as news and weather) being repeated frequently so they would load quickly, and less popular pages taking longer to load (or more accurately, to wait for the next time they appeared in the looped data).

I was interested to see that the Sega system used a bitrate of 8Mbps, which sounded pretty high for the mid-90s, but I see that Teletext had a bitrate of almost 7Mbps for PAL broadcasts, despite being roughly 15 years older!

[1] https://en.wikipedia.org/wiki/Teletext

[2] https://en.wikipedia.org/wiki/Ceefax

[3] https://en.wikipedia.org/wiki/BBC_Micro_expansion_unit#Telet...

[phire]

Teletext had an instantaneous bitrate of 6.9Mbit, but it was only active for a few lines per frame during vertical blanking.

The continuous bandwidth of teletext was only 324 Kbit.

The main innovation of Sega Channel (and similar approaches from about the same time) was allocating a whole TV channel exclusively to data.

[ndiddy]

You got me interested in how the signal was transmitted, so I looked a bit more into it (see https://segaretro.org/File:SegaChannel_Applications_Scientif... ). It turns out that the 8Mbps number I eyeballed from looking at newspaper coverage of the service was incorrect. When the cable provider received the Sega Channel data stream, they'd split it into two 6Mbps carriers. This allowed them to transmit Sega Channel data without having to dedicate a channel to data, as they could put the carriers between cable channels or in the portion of the spectrum used for cable FM radio. I updated the webpage with the corrected figures.

[phire]

Yeah, I was wondering how TV-like this channel looked.

It's tempting to wrap it in fake horizontal/vertical blanking so it still looks like a TV signal (and you can send it through existing equipment that's expecting a TV signal). Essentially just Teletext but using every single line.

But what Scientific Atlanta created is much closer to cable internet. The total bandwidth number is notable, each 6Mbit carrier uses 3Mhz of bandwidth, so the two of them add up to 6Mhz, which is how much bandwidth a standard NTSC channel occupies.

I suspect this is because they have rented a single TV channel worth of bandwidth on the Galaxy 7 satellite for disruption to local cable companies.

Splitting into two 3Mhz carriers has the additional advantage of allowing the receiver design to be simpler, it only needs to tune into one at any time.

[thepolish]

So my question is - knowing that and looking at the marketing literature, is it possible to somehow recreate the signal to use on actual hardware.

It's possible to RF modulate composite sources over coax for home cable systems (think blonder tongue gear or even consumer gear) - since it is combined to the 6Mhz signal somewhere along the line could one not pipe this signal into a coax cable and then into the hardware to recreate it?

Am looking at setting up my own home analog CATV system and this would be the cherry on the cake. I guess the real question is what was the device expecting in that signal - what was being modulated out over the wire.

[nanoxide]

Teletext is still very much alive in Germany, pretty much every channel offers it. In fact, I use it most days to quickly check if there are any interesting headlines to follow up online, or for sports results. It's funny that it is frequently faster and easier to navigate than most enshittified news websites.

[Cthulhu_]

Same in the Netherlands, but it's updated to the modern age with a website / emulator [0] and app [1], both appropriately styled.

[0] https://nos.nl/teletekst

[1] https://apps.apple.com/nl/app/nos-teletekst/id289246732

[tobwen]

It was even crazier in Germany! In 2000, the television station NBC received a radio license for RadioMP3. They broadcasted the charts and entire albums (with covers) via teletext, which could be legally recorded at home. Bit rate 128 kbit/s - simply with a TV capture card. The public broadcaster also transmitted software via “VideoDAT” during its ComputerClub program. However, this required special hardware.

[mcraiha]

Same in Finland. There is a one guy running the show nowadays. https://yle.fi/a/3-12131551 (article only in Finnish)

[andrepd]

I have seen more than one old geezer in NS trains reading the news on the Teletext app on the smartphone :)

Maybe they're into something?

[jamesfinlayson]

At a company I used to work at there was a service that scraped the teletext XML to get some numbers as a second source to double check what was scraped off a website.

[epcoa]

> I was interested to see that the Sega system used a bitrate of 8Mbps, which sounded pretty high for the mid-90s,

This was over cable TV, so not very difficult to obtain these rates compared to general broadcast TV. Cable internet service rolled out in this time period with downstream rates of 40 Mbps per 6 MHz channel.

[wgx]

Thank you for this! You just unlocked some old memories of “Digitiser” which led me here:

https://teletextart.co.uk/artists/paul-rose-mr-biffo