End-Fed Half-Wave Antenna
Building Class
The registration link is :
https://registration.w2mmd.org/wpregp/end-fed-half-wave-antenna-build
https://registration.w2mmd.org/wpregp/end-fed-half-wave-antenna-build
First Class : Saturday, July 11, 2026
Second Class : Saturday, July 18, 2026
Build Your Own End-Fed Half-Wave Antenna : W2MMD Clubhouse
Tech Saturday Forum is back with another hands-on learning and building session and a nice take-home project that you can put on the air right away. Once again Chris Prioli AD2CS will lead the group, this time through the construction of an end-fed half-wave (EFHW) antenna system from scratch. For $60 to $75 in parts and a morning of your time, you will learn the fundamentals of antenna impedance matching, build a weatherproof matching transformer, cut and connect your antenna wire, and leave with a fully tested HF antenna ready to use.
The cost is $60.00 for the 250 Watt, $67.50 for the 750 Watt, or $75.00 for the 1500 Watt antenna.
What Is an End-Fed Half-Wave Antenna?
An EFHW is a single wire antenna fed at one end through a compact 49:1 matching transformer. Cut the wire to a half-wavelength at your lowest desired operating frequency, and the antenna resonates naturally on all harmonic bands above that - with no antenna tuner required. A wire cut for 40 meters works on 40m, 20m, 15m, and 10m. Cut it for 80 meters and you cover the entire HF spectrum from 80m through 10m with a single piece of wire. Part of the morning will be spent understanding why this works - the physics of standing waves, impedance transformation, and why feeding an antenna at its end is both a challenge and an opportunity.
Why Hams Love the EFHW
Beyond the learning experience, the antenna you build is genuinely useful. The EFHW solves several practical problems that get in the way of putting up a good antenna :
Put It to Work on the GCARC WSPR Network
The Club operates a crowdsourced WSPR propagation network, with member beacons monitoring HF band conditions around the clock. The EFHW is an ideal WSPR antenna - it stays connected permanently, covers multiple bands, and its modest footprint means it can be left up year-round without drawing attention. If you have been thinking about contributing a beacon to the Club network, this is your antenna. Build it on Saturday, hang it that afternoon.
What You Will Learn and Build
The project moves through three phases, each one a distinct skill and a piece of the finished antenna :
The completed antenna system includes a sealed weatherproof PVC enclosure, an SO-239 coax connector, two stainless binding posts with wing nuts, a stainless eye bolt for hanging, and a ceramic egg insulator for the far end of the antenna wire.
How to Register
Space is limited, and pre-registration with advance payment will be required to reserve your kit. All materials and test equipment will be provided - there’s nothing that you need to bring.
The registration link is :
https://registration.w2mmd.org/wpregp/end-fed-half-wave-antenna-build
The sign-up period will be short so plan now to attend and build this useful antenna.
Second Class : Saturday, July 18, 2026
Build Your Own End-Fed Half-Wave Antenna : W2MMD Clubhouse
Tech Saturday Forum is back with another hands-on learning and building session and a nice take-home project that you can put on the air right away. Once again Chris Prioli AD2CS will lead the group, this time through the construction of an end-fed half-wave (EFHW) antenna system from scratch. For $60 to $75 in parts and a morning of your time, you will learn the fundamentals of antenna impedance matching, build a weatherproof matching transformer, cut and connect your antenna wire, and leave with a fully tested HF antenna ready to use.
The cost is $60.00 for the 250 Watt, $67.50 for the 750 Watt, or $75.00 for the 1500 Watt antenna.
What Is an End-Fed Half-Wave Antenna?
An EFHW is a single wire antenna fed at one end through a compact 49:1 matching transformer. Cut the wire to a half-wavelength at your lowest desired operating frequency, and the antenna resonates naturally on all harmonic bands above that - with no antenna tuner required. A wire cut for 40 meters works on 40m, 20m, 15m, and 10m. Cut it for 80 meters and you cover the entire HF spectrum from 80m through 10m with a single piece of wire. Part of the morning will be spent understanding why this works - the physics of standing waves, impedance transformation, and why feeding an antenna at its end is both a challenge and an opportunity.
Why Hams Love the EFHW
Beyond the learning experience, the antenna you build is genuinely useful. The EFHW solves several practical problems that get in the way of putting up a good antenna :
- Feed it where it's convenient : Unlike a dipole, which must be fed at its center - often the hardest point to reach - the EFHW is fed at one end. That end can be at a convenient height near your shack, connected with a short run of coax.
- One wire, multiple bands : A single piece of wire covers your primary band and all its harmonics. No traps, no loading coils, no switches.
- Install it any way the terrain allows : Straight, sloped, inverted-L, bent around a corner - the EFHW is forgiving about physical configuration. It works well in the kinds of irregular backyards most of us actually have.
- Low visual profile : A single thin wire between two supports draws far less attention than a center-fed dipole with its visible feed point hardware and hanging feedline - an important consideration for hams in HOA neighborhoods or on restricted properties.
- Portable and field-ready : The matching transformer, wire, and end insulator pack down into a small, lightweight bundle. Throw the far end over a tree branch and you can be on the air in minutes - the antenna of choice for Parks On The Air and emergency operations.
- A great first HF antenna for Technicians : Technicians have limited privileges on 10 meters but this is an ideal antenna for the 10 meter WSPR stations. An EFHW cut for 10m fits in almost any space and is a natural first step onto HF for newly licensed operators.
Put It to Work on the GCARC WSPR Network
The Club operates a crowdsourced WSPR propagation network, with member beacons monitoring HF band conditions around the clock. The EFHW is an ideal WSPR antenna - it stays connected permanently, covers multiple bands, and its modest footprint means it can be left up year-round without drawing attention. If you have been thinking about contributing a beacon to the Club network, this is your antenna. Build it on Saturday, hang it that afternoon.
What You Will Learn and Build
The project moves through three phases, each one a distinct skill and a piece of the finished antenna :
- Toroid winding : You will wind a 49:1 impedance transformer on a ferrite core - 21 secondary turns and 3 primary turns of enameled wire.
- Mechanical assembly : Mounting the SO-239 coax connector, installing the two stainless binding posts with wing nuts, fitting the top eye bolt for hanging, and sealing all penetrations so the enclosure is weatherproof for permanent outdoor use.
- Wire cutting, connection, and testing : You will calculate and cut your own antenna wire to the correct length for your chosen band, connect it to the matching transformer, and sweep the completed antenna on a vector network analyzer. You will see your own SWR curve and understand what it means before you leave.
The completed antenna system includes a sealed weatherproof PVC enclosure, an SO-239 coax connector, two stainless binding posts with wing nuts, a stainless eye bolt for hanging, and a ceramic egg insulator for the far end of the antenna wire.
How to Register
Space is limited, and pre-registration with advance payment will be required to reserve your kit. All materials and test equipment will be provided - there’s nothing that you need to bring.
The registration link is :
https://registration.w2mmd.org/wpregp/end-fed-half-wave-antenna-build
The sign-up period will be short so plan now to attend and build this useful antenna.
The End-Fed Half-Wave Antenna : Why a Transformer Is Essential
By Jon Pearce WB2MNF
This article complements the announcement above of the July 11, 2026 Tech Saturday Forum to build an end-fed half-wave antenna and explains the technical issues surrounding its construction.
The end-fed half-wave antenna has become one of the most popular HF antennas in amateur radio, and for good reason - it is multiband, easy to deploy, and requires only a short coax run back to the shack. But connecting a coaxial feedline directly to the end of a half-wave wire is not straightforward. There is a fundamental mismatch between what the radio expects and what the antenna presents, and understanding that mismatch is the key to understanding why the matching transformer exists.
Standing Waves and the Voltage-Fed Feed Point
When RF energy travels down a wire and reaches the open end, it has nowhere to go and reflects back toward the source. The forward and reflected waves combine to produce a standing wave - a fixed pattern of voltage and current that oscillates in place along the wire's length.
The distribution is predictable and elegant. Current is maximum at the center of the wire and drops to zero at both ends. Voltage is the mirror image - zero at the center and maximum at the ends. This makes physical sense : electrons at an open end have nowhere to go, so current goes to zero there, and the resulting charge buildup drives voltage to its peak.
This is why an end-fed antenna is sometimes called a voltage-fed antenna. You are connecting your feedline at the point of maximum voltage and minimum current. That combination - high voltage, low current - means the antenna presents a very high impedance at its feed point, somewhere in the range of 2,500 to 4,000 ohms depending on frequency, wire height, and nearby objects.
The Mismatch Problem
Your radio and coaxial feedline are designed for a 50-ohm system. Connecting 50-ohm coax directly to a 2,500–4,000 ohm antenna creates an impedance mismatch ratio of roughly 50:1. The consequences are severe :
Simply using an antenna tuner in the shack does not solve this. A tuner can present the correct impedance to the transmitter, but it does not prevent common-mode current from traveling on the coax shield between the antenna feed point and the tuner. The mismatch and its consequences remain at the antenna end.
The 49:1 Matching Transformer (See above picture)
The solution is to place a broadband impedance transformer at the feed point itself - inside the weatherproof enclosure that is the heart of this project. The transformer converts the antenna's ~2,450 ohm feed point impedance down to 50 ohms, right at the point where the antenna meets the coax. With a properly matched feed point, the coax carries only the intended signal and the transmitter sees the load it was designed for.
The impedance transformation ratio is the square of the turns ratio. To step down from ~2,450 ohms to 50 ohms requires a ratio of 49:1, which means a turns ratio of 7:1. In practice this is achieved by winding 3 primary turns and 21 secondary turns - a 7:1 ratio - on a ferrite toroid core. Three turns on the primary side connects to the 50-ohm coax; twenty-one turns on the secondary side connects to the antenna wire.
The Ferrite Core
The toroid core is not just a form for winding wire - it is an active participant in the transformer's operation. The ferrite material (Mix 43 in this project) has high magnetic permeability, which concentrates the magnetic field and allows the transformer to work efficiently across a wide range of frequencies with only a few turns of wire.
Without the core, you would need many more turns to achieve the same inductance, and the transformer would become frequency-selective rather than broadband. The core enables the matching transformer to work from 80 meters through 10 meters with a single winding - the same transformer serves all bands.
The Counterpoise
One remaining problem : a transformer has two sides, and the secondary side needs a return path for current just as much as the primary does. In a center-fed dipole, the return path is the other half of the antenna, which carries equal and opposite current symmetrically. An end-fed antenna has no second half.
Without a return path, current looks for one on its own - and it finds the coax shield. A short counterpoise wire, typically 0.05 wavelengths at the lowest operating frequency, attached to the ground terminal of the matching transformer provides that return path locally. It does not need to be resonant or carefully tuned; it simply needs to exist so that coax shield current is suppressed.
Why Multiband Operation Works
A half-wave wire cut for 40 meters is also a full wave on 20 meters, three half-waves on 15 meters, and two full waves on 10 meters. In each case, the standing wave pattern still places a voltage maximum at the fed end of the wire - the same high-impedance condition exists on every harmonic band. The same 49:1 transformer therefore presents approximately the correct transformation on each of those bands, which is why a single wire and a single transformer can cover four or more bands without a tuner.
This harmonic relationship is the elegant physics that makes the EFHW so practical, and the matching transformer is the device that makes it accessible to a 50-ohm world.
By Jon Pearce WB2MNF
This article complements the announcement above of the July 11, 2026 Tech Saturday Forum to build an end-fed half-wave antenna and explains the technical issues surrounding its construction.
The end-fed half-wave antenna has become one of the most popular HF antennas in amateur radio, and for good reason - it is multiband, easy to deploy, and requires only a short coax run back to the shack. But connecting a coaxial feedline directly to the end of a half-wave wire is not straightforward. There is a fundamental mismatch between what the radio expects and what the antenna presents, and understanding that mismatch is the key to understanding why the matching transformer exists.
Standing Waves and the Voltage-Fed Feed Point
When RF energy travels down a wire and reaches the open end, it has nowhere to go and reflects back toward the source. The forward and reflected waves combine to produce a standing wave - a fixed pattern of voltage and current that oscillates in place along the wire's length.
The distribution is predictable and elegant. Current is maximum at the center of the wire and drops to zero at both ends. Voltage is the mirror image - zero at the center and maximum at the ends. This makes physical sense : electrons at an open end have nowhere to go, so current goes to zero there, and the resulting charge buildup drives voltage to its peak.
This is why an end-fed antenna is sometimes called a voltage-fed antenna. You are connecting your feedline at the point of maximum voltage and minimum current. That combination - high voltage, low current - means the antenna presents a very high impedance at its feed point, somewhere in the range of 2,500 to 4,000 ohms depending on frequency, wire height, and nearby objects.
The Mismatch Problem
Your radio and coaxial feedline are designed for a 50-ohm system. Connecting 50-ohm coax directly to a 2,500–4,000 ohm antenna creates an impedance mismatch ratio of roughly 50:1. The consequences are severe :
- The SWR at the feed point would be 50:1 or worse
- Most modern transceivers fold back power dramatically above SWR 3:1, protecting their output stage
- The small fraction of power that does reach the antenna arrives inefficiently
- Return current has no proper path, so it flows back down the outside of the coax shield, causing the feedline to radiate - bringing RF into the shack, creating interference, and making the antenna pattern unpredictable
Simply using an antenna tuner in the shack does not solve this. A tuner can present the correct impedance to the transmitter, but it does not prevent common-mode current from traveling on the coax shield between the antenna feed point and the tuner. The mismatch and its consequences remain at the antenna end.
The 49:1 Matching Transformer (See above picture)
The solution is to place a broadband impedance transformer at the feed point itself - inside the weatherproof enclosure that is the heart of this project. The transformer converts the antenna's ~2,450 ohm feed point impedance down to 50 ohms, right at the point where the antenna meets the coax. With a properly matched feed point, the coax carries only the intended signal and the transmitter sees the load it was designed for.
The impedance transformation ratio is the square of the turns ratio. To step down from ~2,450 ohms to 50 ohms requires a ratio of 49:1, which means a turns ratio of 7:1. In practice this is achieved by winding 3 primary turns and 21 secondary turns - a 7:1 ratio - on a ferrite toroid core. Three turns on the primary side connects to the 50-ohm coax; twenty-one turns on the secondary side connects to the antenna wire.
The Ferrite Core
The toroid core is not just a form for winding wire - it is an active participant in the transformer's operation. The ferrite material (Mix 43 in this project) has high magnetic permeability, which concentrates the magnetic field and allows the transformer to work efficiently across a wide range of frequencies with only a few turns of wire.
Without the core, you would need many more turns to achieve the same inductance, and the transformer would become frequency-selective rather than broadband. The core enables the matching transformer to work from 80 meters through 10 meters with a single winding - the same transformer serves all bands.
The Counterpoise
One remaining problem : a transformer has two sides, and the secondary side needs a return path for current just as much as the primary does. In a center-fed dipole, the return path is the other half of the antenna, which carries equal and opposite current symmetrically. An end-fed antenna has no second half.
Without a return path, current looks for one on its own - and it finds the coax shield. A short counterpoise wire, typically 0.05 wavelengths at the lowest operating frequency, attached to the ground terminal of the matching transformer provides that return path locally. It does not need to be resonant or carefully tuned; it simply needs to exist so that coax shield current is suppressed.
Why Multiband Operation Works
A half-wave wire cut for 40 meters is also a full wave on 20 meters, three half-waves on 15 meters, and two full waves on 10 meters. In each case, the standing wave pattern still places a voltage maximum at the fed end of the wire - the same high-impedance condition exists on every harmonic band. The same 49:1 transformer therefore presents approximately the correct transformation on each of those bands, which is why a single wire and a single transformer can cover four or more bands without a tuner.
This harmonic relationship is the elegant physics that makes the EFHW so practical, and the matching transformer is the device that makes it accessible to a 50-ohm world.