Building an end-fed half-wave antenna requires a resonant wire, a 49:1 or 64:1 impedance transformer, and careful tuning after the antenna is in its final position.
An end-fed half-wave (EFHW) antenna is one of the most practical HF antennas you can build yourself. A single wire cut to the right length and fed through a small transformer delivers solid performance on one or multiple amateur bands with minimal hardware and a tiny footprint. The build is straightforward—the tuning is where patience pays off.
What Makes an EFHW Antenna Work?
An EFHW antenna uses a wire cut to roughly half the wavelength of the target frequency. The feedpoint sits at one end of that wire, a high-impedance point, so a transformer steps the impedance down to 50 ohms for standard coax. The conventional ratio is 49:1, though 64:1 designs also work well for certain builds. A short counterpoise wire—typically around five percent of the antenna length—connects to the coax shield to stabilize the match and reduce common-mode current on the feed line.
Parts and How to Build Your EFHW
Seven main components go into a basic EFHW build. The table below covers what each part does and what to look for.
| Component | Purpose | Notes |
|---|---|---|
| Antenna wire (14–18 AWG stranded copper) | Radiating element | Cut slightly longer than calculated half-wavelength |
| Toroid core (FT240-43 or T80-2) | Core for the impedance transformer | Size depends on power level and bands |
| Magnet wire (22–26 AWG enameled) | Windings for the transformer | Scrape enamel off ends before soldering |
| Waterproof enclosure | Houses the transformer | A weatherproof plastic box works well |
| SO-239 or BNC connector | Connects coax to the antenna | Requires a 5/8 inch mounting hole |
| Counterpoise wire (same gauge as antenna) | Provides RF ground reference | About 5% of the antenna wire length |
| Coax cable (50 ohm RG-8X or RG-58) | Feeds the antenna from the radio | Keep as short as practical for portable use |
Once you have the parts, the build follows five steps. Start by calculating the wire length using the standard half-wave formula (468 divided by the frequency in MHz) and cut the wire four to six inches longer than the result—you trim to resonance after deployment. Wind the transformer on the toroid core next. Count each pass carefully and keep the windings orderly to avoid detuning the transformer.
Prepare the wire ends by scraping off the enamel, then solder the antenna wire, coax center conductor, and counterpoise lead as your design specifies. Mount the transformer in the enclosure by drilling a 5/8 inch hole for the coax connector—the ARRL’s end-fed half-wave antenna kit instructions describe this exact step—position and mark the mounting holes, and fasten the connector. Add zip ties for strain relief so the wire connections don’t pull on the solder joints. Finally, deploy the antenna in its intended location with the transformer a few feet above ground on a fiberglass mast and the wire running away from conductive objects.
For those who prefer a ready-made solution, our roundup of the best end-fed half-wave antennas compares tested pre-built options for various bands and budgets.
Tuning Your EFHW and Common Mistakes
Tuning is where most builders either succeed or struggle. Deploy the antenna exactly as it will be used—height, angle, and nearby objects all affect the resonant frequency. Connect an antenna analyzer or your transceiver’s SWR meter and check where the lowest SWR falls. If it’s below the target band, the wire is too long; if above, it’s too short. Trim in small increments, two inches at a time on 20 meters, and recheck after each cut until the match lands where you want it.
The most frequent errors include cutting the wire before testing it in the final installation, skipping the counterpoise, using sloppy transformer windings with crossed or overlapping magnet wire, and failing to add strain relief at the connector. A few minutes of careful continuity checking and mechanical reinforcement will save hours of frustration later. Raise the feedpoint several feet off the ground and keep the first section of wire clear of metal objects for reliable performance.
FAQs
What bands can a single EFHW antenna cover?
A single EFHW can be built for one band, or with linked wires it can cover multiple bands from 80 meters through 10 meters. Multiband designs use traps or a long wire that presents an acceptable match on several harmonics of the fundamental half-wave frequency.
Do I really need a counterpoise?
Yes. The counterpoise provides the RF reference the coax shield needs. Without it, the coax itself becomes part of the antenna, causing erratic SWR and RF in the operating position. A short wire, five to ten feet typical, connected to the ground side of the transformer is usually sufficient.
What transformer ratio should I use for a first build?
49:1 is the most common and widely documented ratio for EFHW antennas. It works well for single-band and multiband designs from 40 meters through 10 meters. 64:1 is another valid option used in published DIY designs for specific band sets.
References & Sources
- ARRL. “End-Fed Half-Wave Antenna Kit.” Official kit instructions and assembly documentation for building an EFHW antenna.
Mo Maruf
I created WellFizz to bridge the gap between vague wellness advice and actionable solutions. My mission is simple: to decode the research and give you practical tools you can actually use.
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