Unguided Media

Unguided media transport  electromagnetic  waves without using a physical conductor this type of communication is often referred to as wireless communication.  Signals are normally broadcast through free space and thus are available to anyone who has a device capable of receiving them. Unguided signals can travel from the source to destination in several ways: ground propagation, sky propagation, and line-of-sight propagation.

In ground propagation, radio waves travel through the lowest portion of the atmosphere, hugging the earth.  These low-frequency signals emanate in all directions from the transmitting antenna and follow the curvature of the planet. Distance depends on the amount of power in the signal: The greater the distance.

In sky propagation higher- frequency radio waves radiate upward into the ionosphere (the layer of atmosphere where particle exist as ions) where they are reflected back to earth.  This type of transmission allows for greater distances with lower output power.

In line-or-sight propagation, very high-frequency signals are transmitted in straight lines directly from antenna to antenna. Antennas must be directional, facing each other, and either tall enough or close enough together not to be affected by the curvature of the earth, line-of-sight propagation is tricky because radio transmissions cannot be completely focused.