However, the use of cables to connect transmitters and receivers soon began to show its limitations. By the late 19th century, research was being conducted into electromagnetic waves. The laws of electromagnetic wave propagation showed that information could be transmitted without cables.
The advent of wireless telegraphy and telephony offered enormous potential, despite the poor quality of the first transmissions. Its many applications include the arrival of radiotelephony and the first cordless telephones, as well as radio equipment for maritime safety and military communications.
The relief of the Earth's surface and the huge distances involved (see picture) still posed a problem, though. Due to the number of relay stations required, the system soon proved expensive. It also had limited application for intercontinental links.
Electromagnetic waves travel in straight lines. The Earth, however, is round. This means that signals transmitted over long distances cannot reach the receiver, as the curve of the Earth's surface and other obstacles get in the way. To overcome this problem, relay stations are used.
Satellites make an ideal relay, and are also cheaper.
Since then, numerous satellite-based telecommunications networks have been developed to meet growing demand in a wide range of specialist areas.
GALILEO, the European satellite navigation system
ARGOS, keeping watch over the planet
COSPAS-SARSAT, saving people in distress