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 :-)
[1] https://www.mikrocontroller.net/topic/232846
[2] https://apollo.open-resource.org/mission:log:2014:08:08:darc...
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.
All gone now, it's all 4G.
A few hours drive north of me is Mormond Hill, formerly the site of one part of the North Atlantic Radio System[2]. This used tropospheric scattering and huge dish aerials to communicate radar data down to RAF Fylingdales. There's not much up there now. There were various BT microwave links for offshore oil installations and assorted UHF and VHF links up, but the masts are pretty bare now.
[1] https://en.wikipedia.org/wiki/Meteor_burst_communications
[2] https://en.wikipedia.org/wiki/North_Atlantic_Radio_System
See Minitel from France and Telidon from Canada as other examples of data systems riding on analogue TV and/or POTS telephone systems.
There was a stock fault on BRC 1400 series valve TVs where a resistor in the brightness network would drift high in value and cause uncontrollable bright flyback lines in the upper half of the screen, and you could see those wriggly dotty crawlies ;-) I can't remember the component number - I think I last replaced one when I was 15 or 16, they were the teenage bedroom hand-me-down set of choice in the 80s, absolutely scads of them about in all sizes - but I can still picture in my mind's eye exactly where on the board it is, 220kΩ, red red yellow.
All long gone now, I expect.
If you find one do not re-cap it - the capacitors will be fine. They always are, there aren't any tantalums in it. Instead pay attention to everything above about 200kΩ and find out which ones are now closer to 1 meg!
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.
Some of the limitations are that ham radio requires getting a license (it's easy, but it's a little bit of work and turns some people off), the user base is tiny (it's a niche inside a niche), it requires technical knowledge and specialized hardware, and legally it can't be encrypted or used for commercial purposes. That's okay if your plan is to broadcast messages without censorship, but not so great if you want to check email or browse https sites.
https://spectrum.ieee.org/build-a-longdistance-data-network-...
https://www.reddit.com/r/amateurradio/comments/5bj5w0/intern...
The pages were send one by one so if you typed 200 you would have to wait for page 200 to cycle by. If it had 100 sub pages you would have to wait 100 times as long. I believe more important pages could be send more often or similarly the cycle would skip less important pages. Decent TV's would just store pages and sub pages until the next cycle.
I asked crappy local TV stations what a page would cost but they didn't have anything under 1500 guilders per month (comparable to $1500 today) which was an absurd amount of money for 1kb of hosting.
No wonder that, besides news, subtitles and the tv guide, the thing was entirely filled with lottery phone lines, astrology lines, sex lines and similar trash.
People want to fight orcs and goblins, ride dragons, cast magic missile and save the princess.
That (using teletext) one can update the plot dynamically makes for a fun creative challenge. Should probably draw a giant flow chart with the 999 states. When all pages are used you have to remove things before you can add things.
[0] - https://en.wikipedia.org/wiki/Choose_Your_Own_Adventure
$1500 today is probably in the region of 10s of GB, sure, but that's almost a commodity volume by comparison in terms of supply.
For example, I could have made a page with sub-pages with the menu from various restaurants in town. It didn't occur to me that one could monopolize delivery and squeeze restaurants into handing over a large amount of money per meal. (read: cut a large amount of food) I'm not that kind of entrepreneur. I'm sure they do actually pay ƒ1500 now for a dumb listing on a food delivery website. I thought of it as more of a fun thing to have for the local tv station (that hardly anyone watched)
I was just fooling around really but my main plan at the time was classifieds. The normal formula for those at the time was to deliver the text some place and pay in cash. I had considered a paid phone number but those also cost 1500 + 50% of the call cost. A 3 minute call would work out to cost 3 bucks of which I would get ƒ1.50 and I would need 1000 per month just to pay for the phone line. Absurd prices, local (land line) calls at the time cost 10 cents each for unlimited duration and 35 guilders every 2 months.
For a TV station with less than 100 k "viewers" I don't expect many thousands of classifieds. It wouldn't even fit on the page. Say you can fit 10 of them. Say 300 one day ads per month. As a customer, I wouldn't pay ƒ5 per day. The local newspaper started at ƒ6 and the text will stay there for the entire week.
There are userspace workarounds for much of what was dropped, there were no real upstream maintainer of this stuff, and it was justifiable to drop AX.25 support. I don't really understand any of it, nor am I in the unenviable position of keeping it around/working. But a real mixed bag of ham news, AFAICT.
I made back images and kept a lot of the documentation in case I needed to go back since it was tricky to find the first time.
However once you do get it working it's very satisfying to see a connection through a VHF radio appear in the native linux networking stack. Opens doors to a lot of goofy and fun ideas.
I'm planning on building my own Teletext service at some point as part of a wider analogue TV project. It's a cool form for things like the news because you have to be very concise for it to work in such a constrained format; it's the opposite of today where long-form content that doesn't really say anything is dirt cheap to emit at scale. Some of the British services had rudimentary games too like Bamboozle, a quiz game which relied on hexadecimal pages the remote couldn't enter manually.
One thing I'd also like to reinstate is NICAM digital stereo which British analogue TV used to have, most modulators I've come across only generate a mono FM subcarrier in PAL mode so looks like I'm going to be building my own modulator.
Not talking about stuff that would automatically change the FM station to the one with traffic announcements.
Our ~2012 Škoda Octavia had typical Volkswagen Audi Group navigation built in. It would receive data about traffic jams in the background, and incorporate it into route/navigation decisions.
Not sure if switch from FM to DAB carried that over too. Kind of doubtful since mobile phones took over navigation even before Android/iOS Auto stuff showed up.
