You might think that televisions signals are transmitted exclusively over the airwaves - but that's not so. In fact, transmission from a tower is only the last link in the chain - and even that is changing as television becomes digital and distributed in different ways.
Throughout television history there has always been a large and hidden distribution network - a 'secret' infrastructure of feed points, cables, microwave and satellite links that covers the whole country and circles the globe. For years, this 'hidden' network was only really known to network and broadcast engineers ...
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.
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.
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