Part of our Building Your First Ham Radio Station guide.
The half-wave wire dipole is the antenna every ham radio guide points to first, and for good reason: it’s simple, it’s efficient, and you can build a solid one for well under $30 in parts. Here’s how I put mine together.
What you’ll need
- Stranded, insulated 14 AWG copper wire (THHN or similar), about 100 ft to have room to trim
- Two end insulators (egg or dog-bone style, or cut your own from scrap plastic or PVC)
- One center insulator/feedpoint: a plastic dog-bone, a small project box, or a PVC coupler with an SO-239 mounted on it
- 50-ohm coax (RG-58 for portable/QRP use, RG-8X or RG-213 if it’s a permanent install)
- A PL-259 connector for the coax end
- Paracord or nylon rope for the ends
- A soldering iron, wire strippers, and a multimeter or SWR meter/antenna analyzer
Step 1: Calculate your length
The classic formula for a half-wave dipole is:
Total length (feet) = 468 ÷ frequency (MHz)
Split that number in half for each leg. A few common starting points:
- 80m (3.75 MHz): ~124.8 ft total, 62.4 ft per leg
- 40m (7.15 MHz): ~65.5 ft total, 32.7 ft per leg
- 20m (14.2 MHz): ~33 ft total, 16.5 ft per leg
The 468 constant already accounts for “end effect”: real wire resonates a bit shorter than a true free-space half wavelength. But it’s a starting point, not gospel. Height above ground, nearby trees and structures, and your wire gauge all shift the actual resonant point a little. Always cut it a few feet long and plan to trim.
Step 2: Build the center feedpoint
Mount an SO-239 to your center insulator (a small plastic project box works great and keeps water out). Solder one leg of the dipole to the center pin side, and the other leg to the shield/ground side. Seal any exposed connections, liquid electrical tape or a bit of silicone works well here.
Step 3: Attach the ends and coax
Thread each wire end through an insulator, fold it back on itself, and twist or solder it to itself for strain relief. Don’t rely on the insulator alone to take the tension. Tie paracord to each end insulator for hoisting. Connect your coax to the SO-239 at the center with a PL-259.
It’s worth adding a simple 1:1 common-mode choke (a handful of turns of the coax through a ferrite toroid) right at the feedpoint. It keeps RF off the outside of your coax shield, which helps both your SWR readings and reduces the chance of RF finding its way back into your shack.
Step 4: Hang it up
A flat, horizontal dipole between two supports is ideal, but if you’ve only got one tall support (a tree, a mast), an inverted-V (center high, ends sloping down) works nearly as well and needs less horizontal space. Aim for at least 20-25 ft of height if you can; the higher it is, the better it performs, especially for DX.
Step 5: Trim for resonance
With the antenna up at its intended height, check SWR across the band with an antenna analyzer or SWR meter. If the lowest SWR point is below your target frequency, the antenna is too long. Trim a few inches off each end (not just one side) and recheck. Work in small steps; it’s easy to cut wire off, impossible to put it back on. A well-built dipole should land under 2:1 SWR across most of the band, often closer to 1.5:1 at the design frequency.
Budget tips
- Speaker wire or bell wire works in a pinch if you separate the two conductors, though stranded THHN holds up better outdoors
- Cut end insulators from a scrap plastic bottle or PVC coupling, plenty of hams have done it and it works fine
- A basic RG-58 pigtail and a cheap SWR meter are enough to get a dipole tuned; you don’t need a $300 antenna analyzer to start
That’s really all a dipole is: wire, insulators, coax, and some patience with the trim. It remains one of the best dollar-for-dollar antennas in the hobby.