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A ground-plane antenna capable of handling a full kilowatt can be constructed, using wire elements, for less than five dollars. The secret lies in the use of the familiar type SO-239 coaxial connector. Simply turn the connector upside down (the center terminal pointing up) and solder the vertical element to the terminal. See the sketch in Fig. 1. The four radial wires are soldered to the four holes in the connector and the feed line with a mating connector is plugged into the SO-239.
Fig. 1. Ground-plane antenna made from an SO-239 connector.
For v.h.f. ground planes, the antenna can be made self-supporting and can be mounted by attaching the feed line to a supporting mast. Low-frequency models will require an insulator at the top of the vertical element. The antenna is then suspended from a tree. The radials will also require insulators and guy wires. The radials should "droop" at about 45 degrees in order to obtain a reasonably good 50-ohm match. The lengths of the elements can be found from the formulas:
George Christakes, K9MDE.