What changed
Dipoles and wire antennas — edited Aug 31, 2026 by Unknown editor
This is the first recorded version, so every line is shown as added. Note: Imported from content/wiki
+
A half-wave dipole is two quarter-wave wires fed in the center with coax. It costs about $30, is
+
easy to build, and is the reference every other HF antenna is measured against.
+
+
## Length
+
+
Total length in feet ≈ **468 / frequency in MHz**. On 20 m (14.1 MHz) that is about 33 feet, or
+
16.5 feet each side. Cut long, then trim a few inches at a time and measure SWR.
+
+
## Height and pattern
+
+
- At a half wavelength or more above ground, a dipole radiates usefully at low angles — good for DX.
+
- Below about a quarter wavelength it becomes **NVIS**: nearly all the energy goes straight up and
+
comes back down within a few hundred miles. Excellent for regional emergency nets, poor for DX.
+
- A dipole is broadside-directional; it is quietest off the ends.
+
+
## Variations
+
+
- **Inverted V** — one support in the middle, ends sloped down. Needs one mast instead of two, and
+
works nearly as well.
+
- **End-fed half-wave (EFHW)** — fed at one end through a 49:1 transformer; a single support point
+
and multiband operation make it the favorite portable antenna.
+
- **Doublet with ladder line** — any length, fed with open-wire line and a tuner; works on every
+
band.
+
- **Fan dipole** — several dipoles on one feed point for multiband use.
+
- **Random wire with a 9:1 unun** — cheap, effective, needs a counterpoise and a tuner.
+
+
## Practical notes
+
+
- Use insulated stranded wire; it stretches less and survives weather.
+
- Support ends with rope, not wire, and leave slack for tree movement.
+
- Add a **choke balun** (coax coiled or a ferrite choke) at the feed point, or the coax shield
+
radiates and RF gets into the shack.
+
- Keep the ends away from people and from anything conductive; the voltage there is high.