![]() The term direct link is used to refer to the transmission path between two devices in which signals propagate directly from transmitters to receivers with no intermediate devices, other than amplifiers or repeaters used to increase signal strength. Unguided media provide a means for transmitting electromagnetic waves but do not guide them examples are propagation through air, vacuum and seawater. Examples of this include microwave, radio or infrared. Unguided transmission media are methods that allow the transmission of data without the use of physical means to define the path it takes. With guided transmission media, the waves are guided along a physical path examples of guided media include phone lines, twisted pair cables, coaxial cables, and optical fibers. In many cases, communication is in the form of electromagnetic waves. Many different types of transmission media are used as communications channel. Telecommunications Ī physical medium in data communications is the transmission path over which a signal propagates. The permittivity and permeability of the medium define how electromagnetic waves propagate in it. In optics, an optical medium is material through which light and other electromagnetic waves propagate. Regions of the insulative vacuum can become conductive for electrical conduction through the presence of free electrons, holes, or ions. 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. Historically, science incorporated various aether theories to explain the transmission medium. 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. It may also pass through any physical material that is transparent to the specific wavelength, such as water, air, glass, or concrete. Thus, an optical fiber or a copper cable is used as transmission media.Įlectromagnetic radiation can be transmitted through an optical medium, such as optical fiber, or through twisted pair wires, coaxial cable, or dielectric-slab waveguides. Technical devices can therefore be employed to transmit or guide waves. While material substance is not required for electromagnetic waves to propagate, such waves are usually affected by the transmission media they pass through, for instance, by absorption or reflection or refraction at the interfaces between media. Vacuum or air constitutes a good transmission medium for electromagnetic waves such as light and radio waves. For example, data can modulate sound, and a transmission medium for sounds may be air, but solids and liquids may also act as the transmission medium. Signals are typically imposed on a wave of some kind suitable for the chosen medium. Cutaway diagram of Coaxial cable, one example of a transmission mediumĪ transmission medium is a system or substance that can mediate the propagation of signals for the purposes of telecommunication. ![]()
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