The Acorn Teletext Adapter allowed the BBC Micro to view Teletext transmissions and download software "over the air" (called Telesoftware) that was broadcast as part of the Analogue TV signal. This was a one way system with limited interactivity (you could "reveal" hidden text) but was a useful and solid way of distributing information reaching its peak in popularity in the 1990's before being phased out as the Analogue TV signals are switched off in the UK throughout 2010 to 2012 on a region by region basis. The Ceefax teletext system will finally be turned off for good on the 23rd of October 2012 at 23:30 in Northern Ireland.
My Teletext Adapter became completely obsolete in September 2011 as my television region switched over to a digital signal, but before then, it earnt its keep as a great information gathering tool.
The adapter is capable of being tuned to four different analogue television channels and receiving Teletext signals for each one. Tuning is carried out using the 4 tuning wheels on the read of the adapter. They're very sensitive and tuning in to get a good signal can be tricky but if you're patient you'll get great results.
Switching between the channels and interacting with the Teletext adapter is carried out by way of the function keys on the BBC Micro as can be seen below with the function key strip showing the different functions of the keys. The upper functions on the key strip are reached by using the SHIFT key as a modifier e.g. f0 is the Index function, SHIFT + f0 is the Tuning function. You can also use the numeric keys to type in the number of a