Transmission medium

It may also pass through any physical material that is transparent to the specific wavelength, such as water, air, glass, or concrete.

Sound is, by definition, the vibration of matter, so it requires a physical medium for transmission, as do other kinds of mechanical waves and heat energy.

However, it is now known that electromagnetic waves do not require a physical transmission medium, and so can travel through the vacuum of free space.

Unguided media provide a means for transmitting electromagnetic waves but do not guide them; examples are propagation through air, vacuum and seawater.

Coaxial cable was invented by English physicist, engineer, and mathematician Oliver Heaviside, who patented the design in 1880.

[3] Coaxial cable is a type of transmission line, used to carry high frequency electrical signals with low losses.

Optical fiber, which has emerged as the most commonly used transmission medium for long-distance communications, is a thin strand of glass that guides light along its length.

Four major factors favor optical fiber over copper: data rates, distance, installation, and costs.

Glass is lighter than copper allowing for less need for specialized heavy-lifting equipment when installing long-distance optical fiber.

Multimode fiber uses LEDs as the light source and can carry signals over shorter distances, about 2 kilometers.

[8] Optical fibers typically include a core surrounded by a transparent cladding material with a lower index of refraction.

Multi-mode fibers generally have a wider core diameter[10] and are used for short-distance communication links and for applications where high power must be transmitted.

The term was coined by Indian physicist Narinder Singh Kapany, who is widely acknowledged as the father of fiber optics.

Line of sight transmission is used to medium-range radio transmission such as cell phones, cordless phones, walkie-talkies, wireless networks, FM radio and television broadcasting and radar, and satellite communication, such as satellite television.

Line-of-sight transmission on the surface of the Earth is limited to the distance to the visual horizon, which depends on the height of transmitting and receiving antennas.

Skywave communication is variable, dependent on conditions in the upper atmosphere; it is most reliable at night and in the winter.

In addition, there are several less common radio propagation mechanisms, such as tropospheric scattering (troposcatter) and near vertical incidence skywave (NVIS) which are used in specialized communication systems.