[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.