Tool
Antenna Length Calculator
Lengths for the wire antennas people actually build. Cut a few percent long and trim — shortening a wire is easy, lengthening one is annoying.
Why 468 and not 492?
A half wavelength in free space is 492 / f(MHz) feet. Real wire is not in free space: the ends couple capacitively to their surroundings, which makes the antenna behave as though it were slightly longer than it is. The traditional468 / f folds in roughly 5% of that end effect.
It is an approximation, not a law. The real resonant length shifts with height above ground, wire diameter, insulation, and anything nearby. Expect to trim. That is why every number here is a starting point and aNanoVNA is the best fifty dollars in the hobby — it tells you which direction to trim and by how much, instead of guessing.
Which one should you build?
- Half-wave dipole — the baseline everything else is measured against. Two supports, or one as an inverted V.
- End-fed half-wave — same wire, fed at one end through a 49:1 transformer. One support and one anchor, and it works on harmonics. Needs a common-mode choke, without exception.
- Quarter-wave vertical — no horizontal span, low take-off angle, but it needs radials to be worth anything.
- Full-wave loop — quieter on receive and a bit of gain, at the cost of a lot of wire and supports.
- 5/8 wave vertical — mostly a VHF thing; more gain toward the horizon than a quarter wave, needs a matching network.
HF Antennas for Small Lots compares these honestly, including what each one costs you.