Wire Antenna Calculator

This calculator uses the classic ham-radio rule-of-thumb formulas that derive from a half-wavelength (or related fraction) of wire at your target frequency, adjusted for the fact that wire antennas resonate slightly shorter than a pure free-space wavelength would predict, due to end effects and the wire's velocity factor relative to bare copper in free space. A half-wave dipole uses L(ft) = 468/f(MHz), a quarter-wave vertical uses 234/f, and a full-wave loop uses 1005/f — all scaled by your specified wire velocity factor (95% for bare copper, 93% for insulated wire, since insulation slows the effective propagation speed slightly and shortens the resonant length needed). The end-fed half-wave uses the same 468/f length as a center-fed dipole since it's electrically the same half-wavelength of wire, just fed at one end instead of the middle; the G5RV is a fixed, published 102-foot design rather than a frequency-derived formula, since it's intentionally a compromise multi-band antenna rather than a single-band resonant one.

Height above ground is expressed in wavelengths and used to estimate a rough takeoff angle: antennas mounted low relative to a wavelength radiate more of their energy straight up (good for regional NVIS-style contacts), while antennas a half-wavelength or higher above ground push more energy out at low angles, favoring long-distance DX. Keep in mind these are simplified free-space/half-wave formulas — real-world resonant length also depends on wire diameter, nearby conductive objects, and ground conductivity, so expect to trim a few percent off the calculated length when tuning for lowest SWR on the actual installed antenna.