DIY Antennas You Can Build

Why Build Your Own?

One of the great privileges of the Advanced license is that you can design, build, and modify your own antennas. Home-built antennas can perform just as well as commercial ones — and you'll understand them far better. Here are proven designs you can build with basic tools and materials.

1. Half-Wave Dipole — The Starting Point

The simplest effective HF antenna. All you need is wire, a centre insulator, two end insulators, and some coax.

How to Build It

Calculate the length: Total length = 143 / f_MHz metres. Each leg is half that.
Cut the wire: Use insulated or bare copper/steel wire. Cut a little longer than calculated — you can always trim shorter.
Centre insulator: Connect your coax here. Solder the centre conductor to one leg, the shield to the other. Add a 1:1 choke balun (see below).
Hang it up: As high as you can, ideally at least λ/4 above ground. Between trees, masts, or house to tree.
Trim to resonance: Use an antenna analyser. If the resonant frequency is too low, trim a bit off each end equally.

Quick-Cut Dipole Table

Band	Centre Freq	Total Length	Each Leg
80m	3.6 MHz	39.7 m	19.9 m
40m	7.1 MHz	20.1 m	10.1 m
20m	14.2 MHz	10.1 m	5.0 m
15m	21.2 MHz	6.7 m	3.4 m
10m	28.5 MHz	5.0 m	2.5 m

2. Inverted-V Dipole — The Practical Favourite

Same as a dipole but the centre is supported high (on a mast or tree) and the ends droop down at about 30-45° angles. This is the most practical HF antenna for most backyards.

Advantages over a Flat Dipole

Only needs one high support point (plus two low anchor points)
Radiation pattern is slightly more omnidirectional — better for general use
Takes up less horizontal space
Impedance is slightly lower (~50 Ω) — actually a better match to 50 Ω coax than a flat dipole!

Practical tip: Keep the apex angle greater than 90° (don't let the legs droop too steeply). Angles of 120-140° at the apex work well. Too steep reduces efficiency and lowers the radiation angle excessively.

3. End-Fed Half-Wave (EFHW) — One Support, One Feedpoint

A half-wave wire fed at one end instead of the centre. Very popular for portable operation (SOTA, POTA) because you only need one support point and the feedpoint is at ground level.

The Catch

A half-wave antenna has very high impedance at the ends (~2500-5000 Ω). You need a matching transformer — typically a 49:1 unun (unbalanced-to-unbalanced transformer) wound on a ferrite toroid.

Building an EFHW

Wind a 49:1 unun: 3 turns primary, 21 turns secondary on an FT140-43 or similar ferrite toroid. Primary connects to the coax, secondary to the wire.
Cut the wire: Same length as a dipole (143/f_MHz metres)
A small capacitor (100-150 pF) across the transformer output helps compensation
Throw the far end over a tree using a weight and fishing line. The feedpoint stays on the ground.

Multi-band bonus: An EFHW cut for 40m (20.1 m) also works on 20m, 15m, and 10m with reasonable SWR — because those are harmonically related. One wire, four bands!

4. Fan Dipole — Multi-Band from One Feedpoint

Multiple dipoles of different lengths, all connected at the same centre feedpoint. Each pair of legs resonates on its target band.

Common combination: 40m + 20m + 15m + 10m
All legs connect to the same coax feedpoint
The resonant pair presents low impedance on its band; the others are high-impedance and don't load the system much
Spread the wires apart slightly (30-50 cm between legs) to reduce interaction

5. Quarter-Wave Ground Plane — Simple Vertical for VHF/UHF

Perfect for 2m or 70cm. Uses a chassis-mount SO-239 connector, a vertical radiator, and 3-4 radials.

Building a 2m Ground Plane

Radiator: A piece of stiff wire or brazing rod, 48.8 cm long (λ/4 at 146 MHz), soldered to the centre pin of an SO-239
Radials: 3 or 4 wires, same length, soldered to the SO-239 flange. Bend them down at about 45° from horizontal
Mount: The SO-239 mounts horizontally with the radiator pointing up and radials drooping down

With radials at 45°, the feed impedance is approximately 50 Ω — a perfect match to coax!

Quarter-wave ground plane antenna for 2m

6. Slim Jim — A Better Vertical for VHF

A folded half-wave vertical made from 300 Ω or 450 Ω ladder line. It has about 3 dBd gain (more than a ground plane) and doesn't need radials.

Total length: approximately ¾ wavelength
For 2m: about 150 cm total
The feedpoint is a gap part-way up the shorter stub — position determines the match to 50 Ω
Can be rolled up for portable use

7. DIY Choke Balun — Essential Accessory

Every dipole should have a choke balun at the feedpoint. Here's the simplest effective design:

Get a ferrite toroid — FT240-31 (for HF) or FT140-43 works well
Wind 10-12 turns of your coax through the toroid
Mount at the antenna feedpoint

Alternative: wind 10-15 turns of coax into a coil about 15 cm diameter (an "ugly balun" or "choke balun"). Less effective than the ferrite version but costs nothing.

8. DIY L-Match Tuner — Match Almost Anything

An L-network antenna tuner is the simplest matching network you can build, and it's a great way to understand impedance matching hands-on. It uses just two components — one inductor and one capacitor — to transform your antenna's impedance to the 50 Ω your radio wants.

How the L-Match Works

The "L" refers to the shape of the circuit — one component in series and one in parallel, forming an L shape. There are two configurations:

Step-down (antenna impedance > 50 Ω): Capacitor in series, inductor in parallel to ground
Step-up (antenna impedance < 50 Ω): Inductor in series, capacitor in parallel to ground

The formulas for component values are:

\( Q = \sqrt{\frac{R_{high}}{R_{low}} - 1} \)

\( X_{series} = Q \times R_{low} \qquad X_{parallel} = \frac{R_{high}}{Q} \)

Example: Matching a Random Wire on 40m

Problem: Your antenna analyser shows the antenna is 200 + j0 Ω at 7.1 MHz. You need to match it to 50 Ω.

Step 1: R_high = 200 Ω, R_low = 50 Ω

Step 2: Q = √(200/50 − 1) = √3 = 1.73

Step 3: X_series = 1.73 × 50 = 86.5 Ω (capacitor in series)

Step 4: X_parallel = 200 / 1.73 = 115.6 Ω (inductor in parallel)

Step 5: Convert to component values at 7.1 MHz:

Series capacitor: C = 1/(2π × 7.1×10⁶ × 86.5) = 260 pF
Parallel inductor: L = 115.6/(2π × 7.1×10⁶) = 2.6 μH

Result: A 260 pF capacitor in series with the antenna, and a 2.6 μH inductor from the junction to ground. Simple!

Building a Variable L-Tuner

For a practical tuner that works across a range of impedances:

Variable capacitor: An air-variable capacitor from an old AM radio (typically 10-365 pF) works well for lower HF bands. For higher power, use a wide-spaced transmitting type or a vacuum variable.
Tapped inductor: Wind 20-25 turns of heavy enamelled wire on a T200-2 (red) toroid. Add taps every 2-3 turns. A rotary switch selects the number of turns, changing the inductance.
Switch: A DPDT switch to swap between step-up and step-down configurations
Enclosure: A metal enclosure provides shielding. Connect the case to the ground/shield.

L-Match tuner: series C + parallel L steps high impedance down to 50 Ω

Power handling: At 400W, voltages across the capacitor and inductor can be high. For the example above, the voltage across C is about V = √(P × X) = √(400 × 86.5) ≈ 186V peak. Air-spaced variable capacitors handle this easily, but small trimmer capacitors may arc. When in doubt, use components rated for at least twice the expected voltage.

Advanced license advantage: You're allowed to build and modify transmitting antennas — something Foundation licensees cannot do. Use this privilege! A well-designed home-built antenna tuned with an analyser can outperform an expensive commercial antenna that isn't properly installed.

Tools You'll Need

Antenna analyser (NanoVNA or similar) — essential for tuning. Without one, you're guessing.
Soldering iron — for connecting wires and coax connectors
Wire cutters and strippers
Tape measure
Coax connectors — PL-259 for HF, N-type for VHF/UHF
Wire — stranded copper for flexible dipoles, solid for permanence. "Figure-8" speaker wire works for lightweight portable antennas