Available online
Description
The programme looks at the system parameters in use in the two types of teletext service available experimentally in the U.K.
The programme looks at the system parameters in use in the two types of teletext service available experimentally in the U.K.
| Module code and title: | T321, Telecommunication systems |
|---|---|
| Item code: | T321; 12 |
| First transmission date: | 07-08-1976 |
| Published: | 1976 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:24:23 |
| + Show more... | |
| Producer: | David Saunders |
| Contributors: | David Crecraft; G.(Gaby) Smol |
| Publisher: | BBC Open University |
| Keyword(s): | Ceefax; Display format; Interactive system; Oracle; System capacity; System parameters; Viewdata |
| Footage description: | David Crecraft introduces the programme with a brief demonstration of Ceefax and Oracle. Crecraft uses a t.v. receiver with picture out of synchronisation to point out the lines which carry the digital information stream for Ceefax and Oracle. Crecraft then demonstrates the Ceefax system by dialling up a broadcast page. Gaby Smol, with the aid of an animated diagram, explains how the Ceefax characters are generated on the screen. He goes on to explain how the technique of character rounding improves legibility of characters. Smol next explains how special control characters are used to display characters in different colours and to initiate graphics displays. David Crecraft, with a systems diagram, explains how the broadcast data signal reached the t.v. screen. Crecraft displays the waveforms of the teletext dots on an oscilloscope screen. He then examines them in greater detail using a diagram. Crecraft, with an animated diagram, explains how the bit rate of a teletext data stream can be determined. Using animated diagrams, Gaby Smol explains how the large bit rate of the teletext system is fitted into the bandwidth available in the television system. Smol shows the spectra of ordinary t.v. and teletext pictures on a spectrum analyser to demonstrate that teletext requires a much greater bandwidth than ordinary t.v. video signals. To compare definition of broadcast and teletext pictures, Smol shows a close-up of each. David Crecraft demonstrates the Viewdata teletext system. He uses a diagram to illustrate how information is accessed in this system. Crecraft then uses a systems diagram of the Viewdata system to explain how the system works. He briefly compares this system with broadcast teletext. |
| Master spool number: | 6HT/71994 |
| Production number: | 00525_5231 |
| Videofinder number: | 1353 |
| Available to public: | no |
