When you can't put a wire between two places, you can use wireless. It is possible to send signals through the air, using electromagnetic radiation in the form of radio waves. Radio can also connect people who are moving around - on a ship, on foot or in a vehicle.
In the right circumstances radio signals can be sent and received across great distances, but the range is not unlimited. Radio waves decline in strength over distance and are subject to interference from other sources.
Directing radio waves accurately is not always feasible; they tend to travel outwards along straight lines from the transmitter and may not follow the curve of the Earth.
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