End-Fed Half-Wave Antenna: The Complete Guide for Ham Radio Operators

What Is an End-Fed Half-Wave Antenna?

Definition and Basic Operating Principle

An end-fed half-wave antenna, usually shortened to EFHW, is a resonant wire antenna fed at one end of a half-wave radiator. Instead of feeding the antenna in the center like a classic dipole, the feedpoint is placed at the end of the wire. It is intentionally cut to be approximately a half wavelength on its lowest intended operating band. That half-wave condition creates a high impedance at the end of the wire, which is why a matching transformer is normally required.

The end-fed half-wave antenna has become one of the most popular designs in amateur radio, particularly for portable and field operation. A single wire fed at one end through a 49:1 UNUN resonates on the fundamental frequency and all its harmonics — covering multiple HF bands from one wire and one feedline, with no tuner required on the harmonic bands.

How It Differs from a Center-Fed Dipole

A center-fed dipole has a feedpoint impedance of approximately 73Ω — close enough to 50Ω for direct coax connection with a simple balun. An end-fed half-wave antenna has its feedpoint at the wire tip rather than the center. At the end of a half-wave resonant antenna, the current is at its minimum and the voltage is at its maximum — producing a very high impedance at the feedpoint. This end-of-wire impedance is typically 2,000–5,000Ω, varying with frequency, wire height, and surrounding environment.

Unlike the dipole antenna, which is comprised of two quarter-wavelength wires and fed at its center, the EFHW is a half-wavelength antenna with the coaxial cable for your transceiver attached at one end. This single physical difference — where the feedpoint is located — changes everything about how the antenna must be matched to a 50-ohm transmission line and how it behaves electrically across multiple bands.

Why Hams Choose EFHW Antennas

EFHW antennas are a popular choice among radio amateurs due to their ability to allow multiband operation without the need of traps or stubs, while consuming little space and providing a minimally unpleasant aesthetic impression. Being a single wire, and end fed, it is very easy to set up, often taking only minutes to do, and this makes it ideal for ham radio portable operation, as well as for base station usage.

The EFHW is far more convenient for multi-band portable operation because no tuner adjustments are needed when changing from 40m to 20m to 15m or 10m — the UNUN handles the matching on all harmonic bands. For HOA-restricted properties, a thin-wire EFHW run along a fence line, roofline, or through foliage is nearly invisible from street level. The single feedpoint and lack of a center support makes the EFHW one of the most effective stealth antenna choices for HOA-restricted properties.

The Physics Behind EFHW Operation

Voltage and Current Distribution on a Half-Wave Antenna

Understanding the standing wave pattern on a half-wave antenna is the key to understanding everything about how an EFHW works. Current is maximum and voltage minimum at the center; at the wire end the current is low and voltage is high. This distribution means the wire end is a high-voltage, high-impedance point — the exact opposite of the center, which is the low-impedance point where a center-fed dipole connects to coax.

This has an important safety implication: keep the end clear of people, gutters, and vegetation due to arc and RF-burn risk, and use good insulators. Evaluate RF exposure per FCC §97.13(c). EFHWs can have high end-voltages. Maintain clearances and use proper hardware.

Impedance at the Feed Point: Why It Is So High

The goal of the impedance transformer is to match the 50-ohm impedance of the feedline (coaxial cable) with the potential 3000 to 4000 ohm impedance expected from an end-fed half wave antenna wire radiator. This is to avoid the antenna radiator from acting like a resistor — instead of radiating radiofrequency energy produced by the transmitter, it would otherwise send it back down the coax toward the transmitter.

The exact impedance at the end of the wire is not constant. The challenge with the EFHW is feeding it as the end is a high impedance point, apparently between 2000 and 6000 ohms depending on the surrounding environment. Wire height above ground, nearby conductive objects, wire length accuracy, and even ground conductivity all shift this number, which is why the matching transformer must handle a range of impedances rather than one precise value.

How Propagation Characteristics Compare to Other Wire Antennas

The EFHW behaves differently from a dipole at the same height because it is an end-fed wire, and its radiation pattern depends on its electrical length relative to the wavelength in use. On 40m at low heights, the primary radiation is near-vertical, making it excellent for regional NVIS (Near-Vertical Incidence Skywave) contacts. On 20m and higher, where the wire is multiple half-wavelengths long, the radiation pattern develops multiple lobes, which can favor DX or skip contacts. Modelling indicates a 6m extending fishing pole with an EFHW setup and 20m of wire has low angle for DX on 20m, and mostly NVIS for 40m local/interstate contacts.

The Matching Unit: Heart of the EFHW System

What a 49:1 or 64:1 Transformer Does

Building a high-efficiency 1:49 UNUN (Unbalanced-to-Unbalanced) impedance transformer is the most critical step in erecting a high-performance EFHW antenna for HF amateur radio bands. This comprehensive guide breaks down the essential technical specifications, winding techniques, and assembly steps required to construct a robust 49:1 antenna matching network capable of handling 100W PEP.

The impedance ratio is the square of the turns ratio: Zratio = (Ns/Np)^2. To transform ~2,450Ω to 50Ω, we want (Ns/Np) ≈ √(2450/50) ≈ 7:1. A practical winding is 2:14 or 3:21 turns on a ferrite toroid, yielding ≈49:1. A 49:1 unun is the most common starting point. Some systems may work better with 64:1, depending on the installation.

Toroid Core Selection and Winding Ratios

Core material selection has a significant impact on EFHW transformer performance across the HF spectrum. Mix 43 ferrite (e.g., FT240-43) provides broad HF coverage (3–30 MHz) and is a good general-purpose choice. Mix 52 ferrite (FT240-52) often runs cooler on higher bands with slightly less inductance per turn.

Core material: FT-240-43 toroid (Fair-Rite type 43) for 3–30 MHz. This material has the right permeability and loss characteristics for HF EFHW operation. Type 31 or 61 core material does not work as well for this application. Wire turns: Primary = 2 turns, Secondary = 14 turns. Ratio = 14/2 = 7, impedance ratio = 7² = 49.

A small NP0/C0G capacitor (≈100–150 pF at ≥3 kV) across the primary (50Ω side) improves high-band SWR and reduces core heating by compensating leakage inductance. A 100 pF capacitor can be soldered into place over the primary side of the transformer, to compensate for any unwanted secondary capacity. This will mainly be noticeable on the higher bands, 15 to 10 meters. If you will not be active on 15 to 10 meters, you may leave the capacitor out.

SWR Expectations and Acceptable Ranges

A standing wave ratio of approximately 1.5:1 or lower is a good match. Try different configurations of the antenna before beginning to trim the antenna wire, a couple of inches at a time, to achieve a low SWR on each of the bands. When used at full power rating of 1kW, the antenna must have a low SWR on the band selected and be used on a 50% duty cycle. Any SWR measurement taken with the transformer at the feedpoint should not exceed 1.5:1 with no tuner in use.

Counterpoise and Ground Requirements

Common-mode current is the primary technical challenge with EFHW antennas. Because the antenna is fed at a high-impedance end with an unbalanced UNUN, there is a strong tendency for RF current to flow back down the outside of the coax shield toward the radio — the coax acts as a counterpoise and becomes part of the radiating system.

Installing the transformer with a counterpoise wire prevents forcing the feedline's coax shield to act as the counterpoise. Attaching a counterpoise wire to the common point of the auto-transformer provides the antenna radiator something to push against rather than the coax shield. The counterpoise wire does not have to be similar in length to the main radiator — the antenna works best with a counterpoise length of 0.05λ on the lowest band the antenna wire is cut for.

To prevent coaxial cable radiation and EMI feedback into the radio shack, install an external RF choke (line isolator) on the coaxial cable, positioned 5 to 7 meters away from the UNUN enclosure.

Multiband EFHW Antennas Explained

How a Single Wire Works on Harmonic Frequencies

An EFHW antenna resonates not only at its fundamental frequency but at every integer multiple of that frequency — all odd and even harmonics. This is because at each harmonic frequency, the wire is an exact multiple of half-wavelengths long, creating a standing wave pattern with a voltage maximum (high impedance) at the fed end.

The End Fed Half Wave antenna functions at both odd and even multiples of a half wavelength, which is one of its benefits. There is a voltage point at all odd and even half wavelengths. It can be used on all odd and even harmonics of the fundamental frequency, presenting the same high impedance at these frequencies. This is a key advantage over the center-fed dipole, which only supports odd harmonics efficiently.

Common Multiband Configurations: 80–40–20–10m

The two most common EFHW configurations used by ham radio operators are:

• 40m EFHW (33 feet / ~10m): 33 feet of wire is a half wavelength for the 20-meter band and two times a half wavelength for the 10-meter band. A 33-foot wire cut for 40m also resonates on 20m, 15m, and 10m — four bands from one wire.
• 80m EFHW (66 feet / ~20m): 66 feet of wire is a half wavelength for the 40-meter band, but also a full wave for the 20-meter band, a double full wave for the 10-meter band, and three half-wavelengths for the 15-meter band. A 66-foot wire for 80m as the fundamental covers 80/40/20/15/10m on harmonics. This is a longer wire requiring more support height but delivering full low-band coverage from a single installation.

Non-Harmonic Bands and Additional Loading Coils

The WARC bands (30m, 17m, 12m) are not harmonic bands for either common EFHW length and require a tuner for operation. On 30m, the feedpoint impedance presented to the UNUN is non-resonant and typically shows SWR of 3:1 to 8:1 — workable with a tuner but not without one. An antenna tuner in the shack (or a remote tuner at the UNUN) allows operation on all HF bands including the WARC bands.

Some builders add a loading coil in the wire at a specific point to extend coverage.