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Feedlines - What are they?
Otherwise known as transmission lines, feed lines are used to transfer RF energy between a transceiver and the antenna.
Three types of feed lines are used by amateurs : Coaxial cable, Open Wire and Waveguides. Links to pages describing these feedlines can be found below.
Coaxial Cable is made of a central conductor, surrounded by a layer of insulating material and a second layer of conducting material over that. The inner conductor is either solid copper or stranded copper wire, whilst the outer conductor is either braided wire or a copper sheath. A protective coating covers the conductors. A hardline is coaxial cable in which the outer conductor is solid copper. Typically, coaxial cables used in amateur installations have impedance of either 50 ohms of 75 ohms. The outer conductor of coaxial cable serves to confine electromagnetic energy within the cable.
Open wire feedlines are composed of two conductors arranged side by side (parallel. "Flat" TV ribbon is an example of open wire cable, and has an impedance of either 300 ohms or 450 ohms.
Waveguides are used in microwave transmissions. A waveguide is a hollow tube made of conducting material, typically copper, through which electromagnetic energy is transmitted. The tube serves the same purpose as the outer conductor of coaxial cable, confining electromagnetic energy and directing it along the length of the waveguide.