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==RF Current Flow==Ferrite Chokes and Baluns may be employed to help stop RF currents from flowing where they aren’t wanted. Common-mode RF current on feedline increases the risk of TVI and other types of RF interference (RFI). RF current flows only on the surfaces of conductors. The outside surface of the coax shield is a completely separate conductor from the inside surface so you can think of the outside surface of the shield is part of the outside world. This is where the common-mode currents flow. Common mode current means that the feedline is radiating RF. It is ideal to have only the antenna radiate. Excessive common mode current causes an excess of RF in the shack, which can get into all sorts of things including the building electrical system. To reduce this you can employee chokes and baluns.* common mode choke* feedline choke* mains chokeThey all do the same job – blocking unwanted common-mode RF current on the feedline cable. Chokes may be needed in several different places: at the antenna feedpoint which is considered a balun, at different points on the coax, on other wiring in the shack including computer cables, and on the mains electrical wiring.