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A half-wave antenna can be end-fed or center-fed. An end-fed half-wave antenna may offer mechanical and construction advantages over a center-fed antenna. The radiation pattern for an end-fed half-wave antenna is no different than a center-fed half-wave antenna. Feed-point impedance for an end-fed half-wave antenna is very high and requires a matching system when matching to 50-ohm coax, while a center-fed half-wave antenna easily matches 50-ohm coax since the feed-point impedance is generally 50-75 ohms. The matching system consists of a quarter-wave length of 450-ohm open-wire ladder line and a choke balun for 50-ohm coax. The quarter-wave length transforms a high impedance at the antenna to a low-impedance at the feed point. Constructing the balun is accomplished by wrapping 5 close-wound turns of 50-ohm coax (approximately 56 inches of coax) on a piece of 2" PVC pipe to create a 1:1 balun. The PVC pipe form is actually a 2"x4" pipe coupler and is very inexpensive. An SO-239 coax connector is used to connect the ladder line to the balun.
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