Data Communications

Transmission medium - the physical path between transmitter and receiver in a data transmission system.

      2 Categories
        o Guided transmission media - are those media with some form of conductor that provides a conduit in which electromagnetic signals arte contained.
        o Unguided transmission media - are wireless system. Unguided signals are emitted and then radiate through air or a vacuum.

Metallic Transmission Lines - a transmission line is a metallic conductor system use to transfer electrical energy from one point to another using electrical current flow.

Transverse Electromagnetic Waves
2 kinds of waves
        o Longitudinal – the displacement (amplitude) is in the direction of propagation.
      E.g. surface waves, sound waves.
        o Transverse –the direction or displacement is perpendicular to the direction of propagation.
          E.g. Electromagnetic waves

Characteristics of Electromagnetic Waves
3 primary characteristics
        o Wave velocity – Waves travel at different speeds depending on the type of wave and the characteristics of the propagation medium.
        o Frequency – the oscillations of an electromagnetic wave are periodic and repetitive.
        o Wavelength – the distance of one cycle occurring in space.

Transmission Lines Classifications
    2. classifications
        o Balanced transmission lines - both conductors in a balanced line carry signal currents.
        o Unbalanced transmission lines – one wire is at ground potential, whereas the other wire is at signal potential.

Metallic Transmission Line Types
    • Parallel-conductor transmission lines – comprised of two or more metallic conductors separated by a nonconductive insulating material called a dielectric.
        o Open-wire transmission lines –these two-wire parallel conductors, closely spaced and separated by air..
        o Twin-lead – essentially the same as open-wire transmission line except that the...