Teletext: The Secret TV Internet Hidden in the Broadcast Signal

Got something to say to this podcast? Send a voicemail, and you might hear yourself on the next episode!

Decades before the World Wide Web, millions of people pulled up news, weather, and sports scores on demand from data hidden inside their television signal. Teletext exploited the vertical blanking interval, the brief gap when a cathode ray tube's electron beam resets from the bottom of the screen to the top. In the early 1970s John Adams at Philips Laboratories worked out how to pack digitized text into those unused lines, and a decoder chip in the set turned it into a grid of 24 rows by 40 characters.

This episode explains how a tool first aimed at closed captioning and farm prices became Ceefax, Oracle, and a worldwide standard, and why a one-way broadcast had to send every page on an endless carousel while viewers waited 10 to 30 seconds for theirs. It follows the format into France and Japan, into prison cells where inmates read coded messages, and through September 11, when overloaded news sites crashed and teletext stayed up. It ends in the Netherlands, where 3.5 million weekly users still refuse to let it die.

• In 1976 a television with a built-in teletext decoder cost around 1,000 pounds, a barrier that fell after British broadcasters agreed on a single standard in 1974.
• Japan's JTES system, launched in 1983, sent dot matrix patterns instead of character codes so sets could render kanji, katakana, and hiragana.
• Inmates in Spain and Finland used public teletext chat pages to receive coded smuggling instructions until prisons banned teletext sets.
• Because a transmitter serves one viewer or 50 million with the same bandwidth, teletext kept delivering headlines when news websites buckled in 2001.
• When a Windows update broke the Dutch system called Cyclone in 2023, NOS consulted retired British engineers and built a cloud replacement that mimics the 1980s look.