In wireless transmission media, data is transmitted in the form of electromagnetic waves that do not require any physical conductors for transmission. The waves are broadcast through free space and any device who has permission to connect can receive them.
The three ways in which unguided signals travel are −
It is a method of propagation, in which radio waves travel through the lowest layers of the atmosphere along the earth’s surface, following the earth’s curvature. The frequency of these signals is low (≤ 2MHz), and the distance they travel is directly proportional to the power in signal.
In sky propagation, high frequency radio waves (2–30 MHz) are reflected back from the ionosphere towards the earth’s surface. They can be used to transmit signals over a large geographical area since their distance is not bounded by the earth’s curvature.
In line – of – sight propagation, very high frequency waves ( > 30 MHz ) travel at straight lines from the source antenna (transmitter) to the destination antenna (receiver). These waves are easily disrupted by present of objects in their path. So the antennas are placed tall enough above obstructions. They are unidirectional facing each other.