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What it does
Computes the physical length of a wire or tubing antenna for a given frequency: full wave, half-wave dipole (with per leg length), quarter-wave vertical, 5/8 wave vertical, and a 3 element Yagi starter with reflector, director, and boom spacing. Input is a frequency like "146.52 MHz" or "7.1MHz"; a bare number is read as MHz.
How to use it
Type a frequency, pick the antenna type, and choose wire or tubing (or override with a custom velocity factor from 0 to 1). Results show length in meters and centimeters alongside feet and inches, plus the classic ham radio reference formulas (468/f, 234/f, 143/f) for comparison.
Why this one
Most antenna length calculators only do the half-wave dipole and hide the math behind a single hardcoded constant. This one derives every length from the speed of light and your chosen velocity factor, covers five common antenna types including a Yagi starter, shows both metric and imperial output, and your inputs never leave your device.
FAQ
- Why does my cut length differ slightly from the 468/f formula?
- The 468/f (feet) and 143/f (meters) constants already bake in an assumed 0.95 wire velocity factor and some rounding. This calculator computes the length directly from the speed of light and your chosen velocity factor, so it tracks closer to the physics; the classic formula is still shown alongside for reference and the two normally agree within a percent or two.
- What velocity factor should I use?
- Thin wire antennas typically use 0.95 to 0.96 because end effects and wire diameter shorten the resonant length below the free space value. Thicker tubing elements, common on Yagis and verticals, run closer to 0.97 to 0.98 because a fatter conductor has less end effect per unit length. These are starting points: real world tuning (SWR analyzer, trimming) always wins over any formula.
- Who is allowed to transmit on the frequency I am designing for?
- This tool only computes physical dimensions; it does not check licensing. For who may legally transmit on a given frequency, see the Electromagnetic Spectrum tool, which includes the US allocation chart and amateur radio band privileges by license class.
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