Over 500 million telephones are now in used throughout the world. In just over hundred years since the Scottish born inventor Alexander Graham Bell patented the first telephone in 1876 – telephones have revolutionized world communications.
Today, telephone networks relay not only voices but pictures and written information as well, by land and sea cables and through the air on microwaves, which are super-high-frequency radio waves. Calls can be made across half the world with less than a second delay in connection, and no difficulty in hearing. Multinational companies can even hold cross world video conferences, with executives speaking to each other from one screen to another.
Satellites, microchips and lasers
The modern inventions that have made this revolution possible include space satellites, microchips and laser beams. Early bird, the world’s first commercial satellite, was launched in 1965 by the International Telecommunication Satellite Organisation (INTELSAT).
Now there are about 130 satellites orbiting in space, relaying messages on microwaves from Earth Station to Earth Station. The orbit the earth at heights of about 22,500 miles (36,000 km) above the equator once every 24 hours, so appear to remain in the same place.
From the earth stations, microwaves carrying messages are beamed up to the satellites from huge dish aerials, some of which are 98ft (30 m) across. They are computer controlled so that they will always point directly at the satellite. Microwaves are not only used for satellite links – dish Aerials beam messages across land too, in straight lines from tower is located to ensure a clear path.
Microchips on the satellites amplify the relayed signals. Microchips have also brought about clearer, speedier communication by providing the fastest switching needed for sending telephone messages by digital transmission. And lasers have enabled the use of fibre optic cables – glass thread that carry digital messages at the speed of light, so fast that they could go seven times round the earth in a second.
Telecommunications services now available include fax, radiopaging, cordless telephones, car telephones and even aircraft telephones, allowing passengers to make calls while flying.
Picture Credit : Google