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What is behind your tv

ISDN brochure, 1990

New data down existing wires : splitting the wire

Ever since Bell invented the telephone, the wires have carried analogue transmissions - electromagnetic signals changing in frequency and amplitude as a replica of the speech waves that created them.

But the same copper wires can also carry digital signals - and that extends their capability by a wide margin.

A digital link can carry any kind of digital signal - from computer files to speech, music, photo images and video.

Digital increasingly dominates the communication network, particularly in business. The exchange is digital, their own switchboards and internal telephones are digital and so are the 'exchange lines' that link these together.

These connections can carry any mix of speech, data or fax calls through ISDN (Integrated Services Digital Network). ISDN can also be fed to homes and small companies where the same pair of wires carries both analogue and digital signals.

It's the same with ADSL (Asymmetric Digital Subscriber Line), which uses the wires to carry standard analogue telephone calls as well as an always-on broadband digital connection to the Internet.

Engineer - (TV studio cables) : John Graham

John Graham, born in 1932 was introduced to the phone from an early age. His family had a candlestick phone on a hall table at home, for his fathers' job as a Fleet Street journalist, but he was forbidden to touch it at first.

Following a schoolboy fascination with electronic he became a TV and radio engineer.

While he worked for Southern TV he was controller of the circuits that brought video into the studio from the outside world, which meant a lot of cooperation with British Telecom.

audio clip


They gave me the job of master controller. This was working very closely with British Telecom in monitoring the circuits which were bringing the video circuits into the studio from the rest of the world, particularly network programmes into us, and ITN news. Normally we would employ a permanent circuit, permanent private wire circuits, between various places to the transmitters so that we could talk to them and to London Tower so that we could have our vision circuits switched. These would need to be booked through Faraday House in London, with a couple of weeks notice and it was quite amazing that no matter where you wanted lines run to they'd be able to provide them very, very efficiently.

fun and games

Can you beat our games? Explode equipment to see what's inside, hear the changing sounds of telecommunications, see how telecommunications designs have changed over time or send an e-postacard.

what's on

The UK's first permanent gallery dedicated to the history of information and communication technologies opens in the new Information Age gallery at London’s Science Museum.

audio history

Take a trip down memory lane with extracts of the interviews which have been recorded as part of the Connected Earth oral history programme.

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