End-Fed Half-Wave

Calculate EFHW wire length for ham radio operation and review harmonic-band coverage.

End Fed Half Wave

A half-wave wire fed at one end, commonly through a 49:1 transformer. Popular for portable operation and simple single-wire deployments.

Band

Design Frequency (MHz)

Length Factor (%) Accounts for the typical shortening of a resonant element. Actual length varies with conductor and installation.

Include Harmonic Bands

EFHW Formula

These are the sizing relationships used by this calculator.

Wavelength

lambda (m) = 299.792458 / f(MHz)

Wire Length

Wire length = lambda / 2 * (Length factor (%) / 100)

Harmonic Bands

Harmonic frequency = Design frequency * n

FAQ

What transformer ratio does this EFHW calculator assume?

It assumes the common 49 to 1 transformer arrangement used for many end-fed half-wave antennas.

Will one EFHW work on multiple bands?

Often yes on harmonic bands, but practical matching still depends on the transformer, installation, counterpoise behavior, and tuner choice.

Antenna Calculators

Use these as starting dimensions

Real antennas still depend on environment, conductor diameter, insulation, feed method, and nearby structures. Expect to trim and retune.

Good field workflow

Cut slightly long when possible.
Measure with the feed system you will actually use.
Make small tuning changes and record each one.

Length factor note

This is a starting estimate for the shortening of a resonant element. Conductor size, insulation, mounting height, nearby structures, and feed arrangement can shift the final length.