Astro Hacker News - Reviving Teletext for Ham Radio

thcipriani |next [-]

One of the ironies of a vibe coded VHF teletext is that the LLM-pocalypse prompted dropping low-level network support (AX.25) from the Linux kernel, which is the basis of a lot of ham networking experiments.

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.

nickcw |next |previous [-]

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 :-)

BoxOfRain |root |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 |root |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 |root |parent |next |previous [-]

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 |root |parent |previous [-]

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.

reaperducer |root |parent |previous [-]

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.

BoxOfRain |next |previous [-]

This Teletext emulator displays a few projects recreating various services: https://zxnet.co.uk/teletext/viewer/.

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.

1xn |next |previous [-]

This is fantastic, the article and the implementation, it looks really good. I have been working on a BBS client lately, and Teletext was also on my maybe wishlist for one day. I also dabble with radio, not HAM though, im not licensed. So i'm still a CB radio supporter.

golem14 |root |parent [-]

Maybe I’m getting senile, but the article lacks even the tiniest amount of detail and contains no link to the implementation. I found also nothing on the intarweb about it, other than this article and a few clones of it. I wonder if this is real at all. It’s an IEEE article, so it should be. But I find this lack of detail very depressing.

joezydeco |next |previous [-]

Imagine a meshtastic network of devices across a city or country, broadcasting a set of rotating teletext pages with no ability to censor it. That would be something.

cf100clunk |root |parent |next [-]

The same author dabbled in a similar project, so maybe there's a Teletext over ham radio tie-in possible?

https://spectrum.ieee.org/run-a-meshtastic-bbs

sucrosesucrose |root |parent |next |previous [-]

> with no ability to censor it Except, of course, policemen knocking on your door. Wouldn't be necessary anyways, most people would not even try broadcasting on the mere threat of arrest.

joezydeco |root |parent [-]

Seems like we have all the key technologies to edit anonymously and distribute info P2P-style with no known central control mechanism.

jlarocco |root |parent |previous [-]

There are actually multiple implementation of networking over ham radio (though not using teletext).

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...

rmbryan |next |previous [-]

Please consider framing your project in your mind as a hobby. It’s valuable to the degree that you enjoy it. Learning and other external values don’t have to apply here. Just the fun of doing it can be enough.

cf100clunk |root |parent |next [-]

I'm familiar with the author's past work on ieee.org and have a sense that he likes to write to/for both hobbyist and professional camps:

https://spectrum.ieee.org/u/stephen-cass

threeio |root |parent |previous [-]

Ham radio as a whole is a great hobby to sink your random RF projects into already.. its a hobby within a hobby, no matter what path you may take ;)

6510 |previous [-]

I think you had 999 pages but each page could have 9999 sub pages.

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.

mrkwse |root |parent [-]

Viewing the fee as being for a volume of storage doesn't seem the right perspective. It's $1500 to lease some %age of spectrum for some period. If true Teletext on an analogue signal and broadcast vs cable, then $1500 for 0.05% of the total non-media spectrum doesn't feel like a terrible deal.

$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.