Time is close to see the results of your carefully planned yearlong strategy to get a new POTA friendly radio from your family for Christmas. You are hoping for a KX3, but you will settle for a Xeigu G90. Now, so you don't get caught with your undershorts at ankle level you have three days to think about an antenna you could use for that POTA event. You don't have much time and of course the 1st POTA opportunity would be Friday, December 26, 2025. You better get cracking today!
Tell me how to build an End Fed Half Wave Antenna for 20 Meters
Building an end‑fed half‑wave (EFHW) antenna for 20 meters is a great project—simple, portable, and surprisingly effective. Let’s walk through it step‑by‑step in a way that’s practical, accurate, and easy to follow.
📡 How to Build a 20‑Meter End‑Fed Half‑Wave Antenna
📏 1. Determine the Wire Length
A half‑wave on 20 meters is roughly:
So you’ll need about 33 feet (10.1 m) of wire.
Materials
33 feet of antenna wire (18–22 AWG stranded copper works well)
1:49 or 1:64 matching transformer (you’ll build this)
FT‑240‑43 or FT‑140‑43 toroid core
Enclosure for the transformer
A short counterpoise or ground connection (optional but helpful)
Antenna end insulators
Coax feed line (10–50 ft)
🔧 2. Build the Matching Transformer (49:1 or 64:1)
EFHW antennas need a high‑ratio transformer because the feed‑point impedance is typically 2,000–3,000 ohms.
✅ Winding a 49:1 Transformer
A common design uses:
2 turns for the primary
14 turns for the secondary This gives a 1:49 impedance ratio.
Steps
Wind 2 turns of insulated wire on the toroid (primary).
Wind 14 turns over the same core (secondary), evenly spaced.
Connect the primary to the coax input.
Connect the secondary to the antenna wire and ground lug.
Mount everything in a weatherproof box.
Each of these steps is a list item, so each must be highlighted:
Wind 2 primary turns
Wind 14 secondary turns
Connect primary to coax
Connect secondary to antenna wire
Install in enclosure
🪢 3. Attach the Radiating Wire
Connect the 33‑ft wire to the high‑impedance output of the transformer.
Add an end insulator.
Deploy the wire as:
Sloper
Inverted‑L
Horizontal wire
EFHWs are forgiving—just keep the wire as straight and high as possible.
⚡ 4. Add a Counterpoise or Choke (Important)
Although EFHWs can work without a counterpoise, performance improves with one.
Options:
3–6 ft counterpoise wire connected to the transformer ground
Coax choke 10 ft from feed point (5–7 turns on an FT‑240‑43 or air‑wound)
📡 5. Tune the Antenna
The antenna is tuned by trimming the wire length.
Steps:
Start at 33 ft.
Measure SWR around 14.0–14.35 MHz.
If resonance is low, shorten the wire.
If resonance is high, lengthen the wire.
List items, so each must be highlighted:
Start at 33 ft
Measure SWR
Shorten wire if needed
Lengthen wire if needed
Most EFHWs end up between 31.5 and 33 ft depending on height and environment.
✅ 6. Deploy and Operate
Once tuned, connect your coax, raise the antenna, and enjoy excellent 20‑meter performance. EFHWs are great for:
Portable QRP
POTA/SOTA
Backyard operation
Want to go deeper?
I can help you design:
A multiband EFHW
A transformer optimized for QRP or 100W
A parts list with recommended components
Which direction do you want to explore next?
Absolutely — here’s a clean, complete parts list for building a 20‑meter End‑Fed Half‑Wave (EFHW) antenna. I’ll keep it practical, with each item highlighted so you can dive deeper if you want.
📦 Parts List for a 20‑Meter EFHW Antenna
🧵 Wire & Radiating Elements
33 ft of 18–22 AWG stranded copper antenna wire
End insulator for the far end of the wire
Short counterpoise wire (3–6 ft), optional but recommended
🔄 Matching Transformer Components (49:1 or 64:1)
FT‑240‑43 toroid core (preferred for 100W)
FT‑140‑43 toroid core (fine for QRP)
18–20 AWG insulated magnet wire for transformer windings
#6 or #8 hardware for mounting the toroid inside the enclosure
Ring terminals for clean connections
📦 Enclosure & Connectors
Weatherproof polycarbonate or ABS enclosure
SO‑239 or BNC female connector for the feed point
Stainless screws, nuts, and lock washers
Rubber grommets or cable glands for strain relief
🧰 Optional but Very Helpful
Common‑mode choke (coax choke) materials: FT‑240‑43 or coax for air‑wound choke
Antenna rope or paracord for hoisting the far end
Coaxial feed line (RG‑8X, RG‑58, or similar)
Heat‑shrink tubing for weatherproofing connections
Here’s a practical, buildable overview of a 20‑meter end‑fed half‑wave (EFHW) with a 49:1 transformer, plus simple “drawings” you can follow.
Basic design parameters for 20 meters
Operating band: 20 m amateur band
Center frequency (example):
Free-space half-wave:
Practical wire length (velocity factor, end effect): about (you’ll trim for resonance).
The end-fed half-wave presents a very high impedance at the feed point (typically a few kΩ), so we use about a 49:1 unun to transform that down to roughly .
1. Electrical schematic (49:1 EFHW for 20 m)
Components
Radiator:
Length: Start with about 10.1 m (33 ft) of wire (14–18 AWG insulated copper is common).
Impedance transformer (unun):
Core: One or two FT240‑43 ferrite cores stacked (or similar mix 43 core).
Winding ratio: 2:14 or 3:21 turns (primary:secondary) to get about 1:7 turns ratio → 49:1 impedance ratio.
Wire: Enamelled copper, about 14–18 AWG.
Enclosure: Small weatherproof plastic box.
Coax connector: SO‑239 or N‑female bulkhead.
Optional: 100 pF (3 kV+ ceramic) capacitor across the primary for improved high‑frequency behavior (many designs use it, some don’t).
Strain relief: Eye bolts or screws for antenna and support rope.
Text schematic (functional)
10.1 m (33 ft) wire radiator
────────────────────────────────────────●
|
| High-Z (~2.5–3 kΩ) point
|
┌───────────┴───────────┐
│ 49:1 UNUN │
│ │
Coax shield ────────────────●──────────────┤ Primary: 2 (or 3) │
| │ turns to coax │
| │ secondary: 14 (or 21)│
| │ turns to radiator │
Optional short └───────────┬─┴───────────┬───────────┘
counterpoise wire | |
(0.05–0.1 λ, e.g. 3–6 ft) | |
| |
Coax center ─────────────────────────────● |
|
Coax shield/chassis ground ────────────────────────────●
Optional capacitor: across the primary (between coax center and shield inside the box).
2. Physical “drawing” of the antenna layout
Simple horizontal installation (end-fed from one support)
Tree / mast / support
▲
| 10.1 m (33 ft) wire radiator
|──────────────────────────────────────────────● End insulator
|
Support rope
|
[Weatherproof box]
┌──────────────────────────────────────────────┐
│ 49:1 UNUN + SO-239 connector │
└──────────────────────────────────────────────┘
|
Coax to shack
|
(Optional)
3–6 ft counterpoise wire along ground or fence
You can slope the wire (sloper), run it in an L shape, or slightly zig‑zag it if space is limited; performance will shift but it will still work.
3. Details of the 49:1 transformer winding
Here’s a typical practical way to wind it (single or stacked FT240‑43 cores):
Turn count:
Primary: 2 or 3 turns (coax side).
Secondary: 14 or 21 turns (antenna side).
Arrangement:
Wind both primary and secondary on the same core so they are tightly coupled.
Common method: bifilar start (primary and secondary together for the first few turns) then continue with the secondary alone, but you can also bundle them side‑by‑side with consistent spacing.
Impedance ratio:
Turns ratio .
Impedance ratio . For , , so , matching typical EFHW feedpoint impedance.
4. Mechanical and installation notes
Wire:
Use flexible, insulated copper‑clad or copper wire; 14–18 AWG is a sweet spot between strength and weight.
Support:
One end high in a tree or mast; the transformer box at a lower point, often 2–3 m above ground for safety and convenience.
Counterpoise/choke:
Many EFHW designs either use a short counterpoise (a few feet) or rely on coax as a return path. Adding a few turns of the coax in a choke (air‑wound coil or ferrite beads) near the box helps reduce common‑mode currents and RFI.
Tuning:
Install at your intended height and configuration.
Check SWR around 14 MHz; if resonance is low in frequency, shorten the wire a bit; if high, lengthen it. Trim in small steps (5–10 cm).
5. Schematic summary in words
The coax from your rig feeds a 49:1 unun in a weatherproof box.
The low‑impedance side of the unun connects to the coax; the high‑impedance side connects to one end of a ~10.1 m wire that forms your 20 m half‑wave.
Optionally, a short counterpoise is tied to the coax shield at the box, and a choke is added on the coax just below the box to keep RF off the feedline.