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Reviving Teletext for Ham Radio

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Re: Reviving Teletext for Ham Radio

#21

Post by mschuster91 »

BoxOfRain wrote: post #12
nickcw wrote: post #3

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…

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.

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...

Re: Reviving Teletext for Ham Radio

#22

Post by binome »

Considering how good LLMs are getting at building DSP code now, I expect to see a tidal wave of new digital modes start to pop up now. It's easy to conduct over the air tests on HF using the global kiwisdr receiver network and build agentic experiment, test, evaluate loops on simulated and real RF channels.

Re: Reviving Teletext for Ham Radio

#23

Post by pstuart »

joezydeco wrote: post #4

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.

I can understand the appeal of that, but we live in a post-truth society where facts only matter to those who care about facts.

Re: Reviving Teletext for Ham Radio

#24

Post by Scoundreller »

reaperducer wrote: post #19
BoxOfRain wrote: post #12

Earlier quoted context omitted.

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.

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.

I’m looking forward to cell phones un-shackling themselves from telecom oligopolies through a mix of repurposed satellite uplink and where available: some FM spectrum downlink utilization.

Just stream me the weather, traffic, text msgs & some news stories that a TTS can read out to me.

Won’t work well for streaming a video but for most of us generally on wifi except out-of-doors, I can live with it.

Re: Reviving Teletext for Ham Radio

#25

Post by techcode »

6510 wrote: post #10

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 as…

Considering you're mentioning guilders - was this the thing shown on TV back then https://nos.nl/teletekst?

Re: Reviving Teletext for Ham Radio

#26

Post by forsalebypwner »

golem14 wrote: post #20
1xn wrote: post #16

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.

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.

Thanks, I thought I was going crazy but yeah, I feel the same way. There are soooo many links in the article, and they're almost entirely irrelevant. It feels like browsing the web with adware installed on your computer in the early 2000s

Re: Reviving Teletext for Ham Radio

#27

Post by LandoCalrissian »

thcipriani wrote: post #17

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 t…

I didn't see it got dropped, that is very unfortunate but also understandable. It's been a few years since I last messed around with it. If I recall, what was in the kernel at the time had a few issues and hadn't been touched in a very long time. It was a huge hassle to get working, there wasn't much up to date documentation.

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.

Re: Reviving Teletext for Ham Radio

#28

Post by techcode »

I recently learned that captions on BBC are teletext based (page 888) so I turned them on and got surprised that it's still working that way - especially considering I'm watching it basically via IPTV (using Dutch KPNs Android SmartTV app).

Re: Reviving Teletext for Ham Radio

#29

Post by ErroneousBosh »

nickcw wrote: post #3

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…

> 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.

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!

Re: Reviving Teletext for Ham Radio

#30

Post by ErroneousBosh »

BoxOfRain wrote: post #12
nickcw wrote: post #3

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…

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.

Up here in the north of Scotland the various council water and drainage departments often had to send data from remote data loggers (high tech stuff in the early 80s). Some of them would transmit a little ping of data every few seconds and if it heard a reply it would send several bursts of data quickly, using meteor scatter[1] to get it back to the receiving station hundreds of miles away.

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

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