What is an end-fed half-wave antenna?
An end-fed half-wave (EFHW) antenna is a half-wavelength wire fed at one end. At the end of a resonant half-wave wire the current is minimum and the voltage maximum, so the feed impedance is high, typically a few kilohms, and is matched to 50 Ω with a broadband transformer (commonly 49:1 or 64:1 on a ferrite core) or a parallel-tuned circuit.[1][2]
Why is the impedance so high?
A half-wave wire’s current distribution vanishes at the ends; feeding there means the same power is delivered at small current and large voltage. The exact value depends on wire diameter, height and surroundings.[2][1]
Is an EFHW multiband?
Yes on harmonically related bands: a wire that is λ/2 on 7 MHz is about 1λ on 14 MHz and 2λ on 28 MHz, all presenting high end impedances. Pattern lobes multiply on higher bands.[1]
Does an EFHW need a counterpoise?
The feed current is small but not zero, so a short counterpoise or the coax shield provides the return; a common-mode choke placed some distance down the coax controls how much of the line participates.[1] See common-mode currents.
Frequently asked questions
What is the turns ratio of a 49:1 transformer?
7:1, since impedance scales with the square of the turns ratio.
Is an EFHW the same as a random wire?
No; the EFHW is resonant at λ/2 and fed through a high-ratio transformer; a random wire is arbitrary length with a tuner.
Why is it popular for portable use?
Single support point and no balun at the center.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “The ARRL Antenna Book for Radio Communications”. ARRL. multiple editions.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.