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Understanding Half-Wave Dipole Antennas

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The half-wave dipole is one of the most popular and useful antennas used in Amateur Radio. A half-wave dipole is open and fed with coaxial cable (often RG-8 or RG-58) at the center and its total length is one-half of the desired wavelength. To determine the total length of a dipole antenna, use this formula:

Length (ft.) = 468 / Frequency (MHz)

For example, let's build a dipole antenna for a desired operating frequency of 29.250 MHz. Using our formula, we would divide 468 by our operating frequency to obtain our half-wave dipole length in feet (468 / 29.250 = 16). We would then cut a 16-ft. length of heavy-gauge insulated wire in half and end up with 8 feet on each side of the insulator.

Always check the standing-wave ratio (SWR) of any antenna you build. If the SWR is above 2:1 you should consider adjusting the antenna as a SWR this high could damage your equipment.

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