That brings back fond memories of my first employer in the early 90s.

They used to rent a single scan line (VBI) of the TV broadcast to use as a data transmission method encoded the same way Teletext was. IIRC you could fit 45 bytes in a single scan line, with 50 per second that gives you a nationwide data broadcast capability of something like 18 kbit/s. We had a 19,200 bits/second leased line to send the data.

That scan line was really really expensive I seem to remember! If your TV wasn't quite adjusted properly you could see the data scan lines at the top of the screen as flickering white dots and lines which was fun.

The data got sent to financial institutions for real time stock feeds and nationwide networks of shops.

I never worked on the code for that part of the business though - I worked on the replacement system which ran via satellite with much more bandwidth at much lower cost.

Eventually the internet killed that too :-)

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BoxOfRain an hour ago | parent | next [-]

I love learning about pre-internet ways of transferring data on the back of other things. Another cool example is that the UK is only shutting down its longwave AM radio service this month (as opposed to decades ago) because the carrier is phase-modulated with data telling older electric meters to switch over. For years this was the only reason such an antiquated radio system stayed alive.

	▲	cf100clunk an hour ago \| parent \| next [-]
		> I love learning about pre-internet ways of transferring data on the back of other things See Minitel from France and Telidon from Canada as other examples of data systems riding on analogue TV and/or POTS telephone systems.
	▲	mschuster91 15 minutes ago \| parent \| prev \| next [-]
		In Munich (Germany), a lot of the displays at bus and tram stations get their data via a side leg on the FM radio broadcast of local station B5 aktuell [1]. More details are here [2], apparently it's called "Axentia iBus FM/DARC". [1] https://www.mikrocontroller.net/topic/232846 [2] https://apollo.open-resource.org/mission:log:2014:08:08:darc...
	▲	reaperducer 23 minutes ago \| parent \| prev [-]
		I love learning about pre-internet ways of transferring data on the back of other things. I once worked for a radio station that made 90% of its revenue from carrying data feeds on subcarriers, and not from main music programs. Because of the geographic location and size of the signal, it was a vital link between two major cities before planting fiber optic lines became cheap.

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reaperducer 25 minutes ago | parent | prev [-]

They used to rent a single scan line (VBI) of the TV broadcast to use as a data transmission method

In the days before cable TV was widespread, there were over-the-air devices to give you a "TV Guide" page, like your cable/satellite service does now.

It was a tiny gray box about the size of a VHS tape, with a cute antenna sticking out of the top.

It constantly received program listing data through scan line data services, and filtered the listing by your ZIP Code. It displayed its TV Guide page on channel 3 or 4, and passed through the rest of the spectrum from your antenna. Because of this, it could even switch channels for you.

It cost something like $40, and after that was a totally free service, with no advertisements.

I'm pretty sure I got mine at Radio Shack, so it's probably listed in the catalogs around 1994 or so.