One thing that has extended the use of the telephone system is the way that new machines, like computers and faxes, have been connected to the existing network - the cables and exchanges that form the telephone infrastructure.
To take advantage of this infrastructure, the machines are designed to work with the existing system. This means that the signals have to be in a range that the telephone wire can handle.
As the telephone is designed to carry speech, you can hear strange whistling sounds coming out of modems and fax machines - they are communicating with each other in the range of the human ear.
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Visit our interactive demonstration and try it for yourself. A new window will open.Eddie Donald, born in 1943, grew up in Fife, Scotland. His family had a phone at home to support his father's work as an engineering contractor.
He was always fascinated by how it worked, but soon learned the science behind it afterwhich the telephone was just accepted as an everyday item.
Eddie became a construction engineer working for an American subsidiary company. They depended on contacting the States via telex, but he was incredulous when the fax was introduced.
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Inside the fax machine : which bit does what?Visit our interactive demonstration and try it for yourself. A new window will open.