How Teletext Worked

The following post was originally made in 2015 to accompany what was originally called "informative strips," now called Snacking Otaku.

To prevent readers from over-analysing this, some of the names in this 
graphic are completely made up.

How many of you remember teletext systems? I suspect many Europeans do (They didn't take off in America).

For those who have no idea what I'm talking about, a teletext system was a means of transmitting computer-generated pages of information to a wide population though TVs with special decoders via the analogue TV picture signals. It was an analogue internet (without the hyper-links, gifs, jpegs, and video streams).
They were first developed in the early-1970s and became widely-available across the globe by the 1980s, particularly in Europe. These systems were known under many names, such as Ceefax and ORACLE in the UK, Antiope in France, Televideo in Italy, Austext in Australia, and (after the demise of ORACLE) .... Teletext.
As they were carried by the picture signals, different TV channels can carry different teletext services from one another, which was truly the case in the UK. The BBC carried Ceefax while the independent channels of ITV, Channel 4 and (later) 5 carried ORACLE (which later became Teletext).
These systems were used a lot (as much people use the web services today). My dad regularly used it during the 1990s and early-2000s to check sports results. I did my self as a teen to check cinema listings. Many people did at the same time for various reasons, from checking the weather forecast to noting down recipes.
These systems only really came to an end in the last decade or so, with the transition to digital TV broadcasting. Ceefax ended in October 2012 (at the same time the last analogue TV transmitter in the UK was shut down).

The reason for this post was not to be nostalgic about teletext (mostly). The reason for this post is to celebrate a personal piece of investigatory achievement - I had finally found/worked out how teletext worked.

I bet many of you who have used such services in the past wondered how they actually worked. How did these pages of information got into your TV and where did they come from (and why you had to wait about ten seconds for your desired page to appear on screen). But when it came to finding out how it worked, most of you found only sources like this one....

(taken form my collection of old reference books)

From Reader's Digest How Is It Done? (1992 edition, p219)

It doesn't tell you much, does it. And with this level of information in regular reference books, you'll imagine that you had to study electrical engineering journals to find out more detail. Fortunately, the internet has made this of an issue, and thanks to this it was in 2013 that I finally found out how teletext worked... and discovered how neat an idea teletext was. How they actually worked is very clever. But its hard to understand using text alone. It'll help if we had pictures. That is why the subject of my next "informative strip" is teletext.

The (what use to be called) "informative strip" can be accessed by clicking here