Ham Radio Dipole Antennas — Complete Guide
The half-wave dipole is the fundamental antenna of amateur radio — the starting point for every operator and the reference against which all other antenna designs are measured. This guide covers everything about dipole antennas: how they work, every major variant, design formulas for all HF bands, feed systems, installation, and tuning. Whether you are building your first antenna or adding to an established station, the dipole remains one of the most effective and versatile choices in amateur radio.
Half-Wave Dipole
The standard horizontal dipole — two equal-length wire legs fed at the center. Resonant on a single band, omnidirectional in azimuth (figure-8 pattern), and balanced. The reference antenna for all gain comparisons.
Inverted-V
Both legs slope downward from a single center apex. One support point instead of three. Slightly more omnidirectional pattern than a flat dipole. Feed impedance drops toward 50Ω at typical apex angles — often requiring no additional matching.
Fan Dipole
Multiple parallel dipole elements sharing one feedpoint, each cut for a different band. No traps, no tuner needed on the covered bands. True resonant performance on each band from a single coax run.
Trap Dipole
Resonant LC traps at specific points along the legs electrically shorten the antenna on higher bands, allowing a single-wire dipole to cover multiple bands at reduced physical length. Each trap introduces small loss.
Off-Center-Fed Dipole (OCFD)
Fed 1/3 from one end rather than at the center. The asymmetric feedpoint creates multiple resonances covering 80m through 10m from one wire with a 4:1 current balun. Also known as the Windom or Carolina Windom.
NVIS Dipole
A standard dipole intentionally mounted very low — 8 to 12 feet above ground — to produce high-angle radiation for Near Vertical Incidence Skywave regional coverage on 40m and 80m. Essential for emergency communication.
Attic / Stealth Dipole
A dipole installed inside an attic or run as a stealth wire along a fence or roofline. Performance is reduced by proximity to building materials but provides HF operation where no outdoor antenna is possible.
ZS6BKW / G5RV
A 102-foot doublet with a specific-length ladder line matching section. The ZS6BKW improves on the original G5RV with optimized matching section length for lower SWR on more bands. Covers 40m through 10m.
Resonance, Current, and Voltage Distribution
A half-wave dipole works because RF current flows along its length in a specific standing-wave pattern. At the resonant frequency, the antenna is exactly half a wavelength long electrically — current is maximum at the feedpoint (center) and tapers to zero at the tips. Voltage is maximum at the tips and minimum at the center.
This current distribution is what produces radiation. Moving charges (current) produce electromagnetic fields — the stronger and more ordered the current distribution, the more efficiently the antenna converts transmitter power into radiated electromagnetic energy.
At resonance, the reactive component of the antenna's feedpoint impedance is zero — the antenna presents a purely resistive load of approximately 73 ohms to the feedline. This makes resonant antennas easy to feed efficiently without complex matching networks.
Radiation Pattern — What It Looks Like
A horizontal half-wave dipole produces a characteristic figure-8 radiation pattern in the horizontal plane. The antenna radiates most strongly broadside — perpendicular to the wire — and has deep nulls off each wire end. In three dimensions, the pattern resembles a toroid (donut shape) wrapped around the wire axis.
In the vertical plane, the pattern shape depends heavily on height above ground. Height determines both the takeoff angle and the gain above the horizon:
- At λ/8 height (~16 ft on 20m): peak radiation at ~60° elevation — NVIS, regional propagation
- At λ/4 height (~33 ft on 20m): peak at ~28° — good regional and DX coverage
- At λ/2 height (~66 ft on 20m): peak at ~14° — excellent low-angle DX radiation
- At λ height (~130 ft on 20m): peak at ~7° — outstanding long-path DX
The practical conclusion: every foot of additional antenna height improves DX performance. The gain improvement from raising a 20m dipole from 30 feet to 50 feet is real and measurable on air.
Gain and radiation patterns guide →Feed Systems — Baluns and Coax
A dipole is a balanced antenna — both legs carry equal and opposite current. Coaxial cable is unbalanced. Connecting the two without a current choke allows RF to flow on the outside of the coax shield, causing the feedline to radiate and making SWR measurements unreliable.
The correct feedline arrangement for a coax-fed dipole:
- Use a 1:1 current choke (current balun) at the feedpoint — wound on FT-240-31 for 3–30 MHz or FT-240-43 for 1.8–10 MHz
- Aim for at least 1000Ω of choking impedance at the operating frequency
- Connect coax center conductor to one leg, braid to the other — polarity does not matter for a dipole
- Leave a drip loop in the coax below the feedpoint to prevent water wicking into the connector
- Weatherproof with self-amalgamating tape from below upward
Alternatively, a dipole can be fed with balanced ladder line through a 1:1 or 4:1 balun at the radio — this allows multi-band operation with a tuner at very low feedline loss regardless of SWR.
Balun and choke guide →Why Height Matters More Than Almost Anything Else
Experienced HF operators consistently prioritize antenna height above every other station improvement — more than power, more than coax quality, and often more than antenna type. The reason is clear in the numbers:
- Raising a 20m dipole from 30 to 60 feet improves low-angle gain by approximately 3–4 dB
- 3 dB is equivalent to doubling transmitter power — a free power doubler
- The improvement is on both transmit and receive simultaneously
- Height improvement comes with no additional noise, no RF management issues, and no matching complexity
- A dipole at 70 feet regularly outperforms a modest Yagi at 30 feet on 20m DX paths
The practical guide: get the feedpoint as high as possible, then let the legs hang at whatever angle the available supports allow. An inverted-V at 50 feet beats a flat dipole at 25 feet for DX operation.
| Band | Frequency Used | Total Length (ft) | Each Leg (ft) | Total Length (m) | Each Leg (m) | Free-space λ (ft) | Typical SWR at Resonance |
|---|---|---|---|---|---|---|---|
| 160m | 1.900 MHz | 246.3 ft | 123.2 ft | 75.1 m | 37.5 m | 516 ft | 1.2–1.5:1 |
| 80m | 3.750 MHz | 124.8 ft | 62.4 ft | 38.0 m | 19.0 m | 262 ft | 1.2–1.5:1 |
| 60m | 5.370 MHz | 87.2 ft | 43.6 ft | 26.6 m | 13.3 m | 183 ft | 1.2–1.5:1 |
| 40m | 7.200 MHz | 65.0 ft | 32.5 ft | 19.8 m | 9.9 m | 136 ft | 1.1–1.4:1 |
| 30m | 10.125 MHz | 46.2 ft | 23.1 ft | 14.1 m | 7.0 m | 97 ft | 1.1–1.4:1 |
| 20m | 14.200 MHz | 33.0 ft | 16.5 ft | 10.1 m | 5.0 m | 69 ft | 1.1–1.3:1 |
| 17m | 18.120 MHz | 25.8 ft | 12.9 ft | 7.9 m | 3.9 m | 54 ft | 1.1–1.3:1 |
| 15m | 21.200 MHz | 22.1 ft | 11.0 ft | 6.7 m | 3.4 m | 46 ft | 1.1–1.3:1 |
| 12m | 24.940 MHz | 18.8 ft | 9.4 ft | 5.7 m | 2.9 m | 39 ft | 1.1–1.3:1 |
| 10m | 28.500 MHz | 16.4 ft | 8.2 ft | 5.0 m | 2.5 m | 34 ft | 1.1–1.3:1 |
All lengths calculated using 468/f(MHz) for total length. Cut 3–5% long and trim to resonance after installation. Actual resonant length will vary with height, wire insulation, and surrounding environment.
What Is an Inverted-V and How Does It Differ?
An inverted-V is a dipole configuration where both legs slope downward from a single center apex support. Instead of requiring three support points (two ends plus a center mast), the inverted-V needs only one — the center mast. The wire ends can be tied to low points like fence posts, tree branches, or stakes driven into the ground.
The practical advantages over a flat dipole are significant for most home installations:
- Only one tall support required — a single mast, tree, or tower
- Legs can run in any direction from the apex — flexible for irregular lots
- The legs are less likely to interfere with property boundaries
- Wire ends at low height are easy to access for adjustments
- Feed impedance naturally falls near 50Ω at common apex angles, simplifying matching
Inverted-V Dimensions and Feed Impedance
An inverted-V uses the same wire length formula as a flat dipole (468/f for total length in feet) but the effective resonant length is slightly affected by the leg angle. As the apex angle decreases (legs more steeply angled), the resonant frequency shifts lower — the effective electrical length increases slightly.
Feed impedance changes with apex angle:
- 180° (flat dipole): ~73Ω — standard dipole impedance
- 120° apex angle: ~65Ω — common practical inverted-V, close to 50Ω
- 90° apex angle: ~50Ω — very close to 50Ω, often no matching needed
- Below 90°: impedance continues dropping; gains in omnidirectionality but loses some gain
Recommended minimum apex angle: 90°. Below 90°, the antenna becomes increasingly omnidirectional but gain drops noticeably compared to a flat dipole. The wire tips should be at least 6–8 feet above ground to avoid detuning by ground proximity and to keep them clear of people and animals.
Complete 20m Dipole Build — Step by Step
Everything from wire cutting to verified resonance on 14.200 MHz.
Calculate and Cut Wire
468 ÷ 14.200 = 32.96 ft total. Cut two legs at 17.0 ft each — 3% longer than the 16.48 ft calculated leg. This gives trimming room. Use #14 AWG stranded copper-clad steel wire for permanent installations.
Wind the Current Choke
Wind 8–10 turns of RG-8X coax through an FT-240-31 toroid core. Keep turns tight and consistent. This provides at least 1000Ω of common-mode choking impedance on 20m — essential for accurate SWR readings and to prevent feedline radiation. Alternatively, use a commercial 1:1 current balun rated for your power level.
Build the Feedpoint
Use a commercial dipole center or fabricate one from PVC and stainless hardware. Strip 1.5 inches of coax jacket and braid. Solder the center conductor to one leg, braid to the other. Heat the wire first — touch solder to the joint, not to the iron. Good joints are shiny and flow completely around the wire. Dull or grainy joints will fail within months.
Attach End Insulators and Rope
Thread each wire tip through an end insulator. Secure with a split-bolt connector or loop-and-solder. Attach UV-resistant Dacron polyester rope to each insulator — minimum 12 inches of rope between insulator and support point. This rope gap prevents the support from detuning the element.
Raise and Support the Antenna
Get the feedpoint as high as possible — this is the single most important installation decision. For an inverted-V, raise the center support first, then tension the wire ends and secure them. For a flat dipole, raise the center and both ends. Leave a drip loop in the coax just below the feedpoint — the coax should descend and then loop upward slightly before running down to the shack.
Initial SWR Sweep
Connect a NanoVNA at the shack end of the coax. Sweep 13.5 to 15.5 MHz. Find the frequency of minimum SWR — this is the antenna's actual resonant frequency. The SWR at the dip should be 1.5:1 or better. If it is higher, check all connections and verify the current choke is working before trimming any wire.
Trim to Target Frequency
If resonance is below 14.200 MHz, trim both legs equally — 2-inch increments on 20m shifts resonance approximately 15–20 kHz. Re-sweep after each trim with the antenna at full height. If resonance is above 14.200 MHz, extend each leg by splicing additional wire. Record every trim and the resulting resonant frequency.
Weatherproof and Verify
Wrap the feedpoint with self-amalgamating tape starting from below the connector, with 50% layer overlap, ending well above the coax entry. Add a PVC electrical tape outer layer for UV protection. Perform a final SWR sweep — if readings have shifted from before weatherproofing, a tape layer is interfering with the connector; recheck. Record the final wire lengths and resonant frequency.
Using a Single-Band Dipole on Other Bands
A half-wave dipole cut for one band will resonate on its odd harmonics — a 40m dipole also resonates on 15m (3rd harmonic). On other bands, the impedance will be non-resonant and variable, but the antenna can still radiate effectively with an antenna tuner to match the feedline.
- 40m dipole resonates on: 40m (fundamental) and 15m (3rd harmonic)
- 80m dipole resonates on: 80m and 40m (2nd harmonic — note: NOT a true resonance but close enough for a tuner)
- 20m dipole resonates on: 20m and 10m (2nd harmonic)
- A tuner and current choke allow operation on any band — efficiency varies
- Ladder line feed with a balanced tuner at the radio gives lowest loss on off-resonance bands
For dedicated multi-band operation without a tuner, a fan dipole, trap dipole, or OCFD provides better efficiency across all covered bands than forcing a single-band dipole to work on non-resonant frequencies.
Multiband antenna options →Antenna Tuners with Dipoles
An antenna tuner (ATU) does not improve the antenna — it presents a 50Ω load to the transmitter regardless of what the antenna actually looks like. What it does do is allow the transmitter to deliver full power into a mismatched antenna, and it protects the finals from operating into a high-SWR load.
Tuner placement matters significantly:
- Shack tuner (at the radio) — corrects SWR at the radio but does not reduce SWR-related coax loss. The coax still sees high SWR and loses additional power as heat.
- Remote tuner (at the antenna) — corrects SWR at the feedpoint, eliminating SWR-related coax loss entirely. The coax runs at 1:1 SWR from tuner to radio. Significantly more efficient for multi-band operation over long coax runs.
- Ladder line + balanced tuner — eliminates SWR-related coax loss completely. The low-loss ladder line handles high SWR with minimal penalty. Best system for multi-band wire antenna operation.
How long should a 20m dipole be?
A 20m half-wave dipole total length is 468 ÷ 14.200 = 32.96 feet, with each leg approximately 16.48 feet. Cut both legs to 17 feet and trim to resonance after installation — the actual resonant length will differ slightly based on height above ground, wire insulation, and surrounding environment. On 14.200 MHz, each inch trimmed from both legs raises resonance by approximately 10–15 kHz.
Dipole calculator →What is the feed impedance of a dipole and does it matter?
A half-wave dipole in free space has a feedpoint impedance of approximately 73 ohms — close enough to 50 ohms that most installations work acceptably with a 1:1 current choke and no additional matching. In practice, proximity to real ground shifts the impedance, which can range from 50 to 90 ohms depending on height and surroundings. An inverted-V at a 120-degree apex angle naturally falls near 65 ohms, and at 90 degrees near 50 ohms — often requiring no matching at all beyond the current choke.
Does a dipole need to be perfectly horizontal?
No — a dipole works in any orientation. Horizontal, inverted-V, sloper (one end high, one end low), or even vertical (though a vertical dipole has a different pattern than a vertical monopole). The orientation affects radiation pattern and polarization but does not prevent the antenna from working. For most HF DX operation, horizontal orientation produces the most useful radiation pattern. A sloper — one end attached to a mast and the other at ground level — is a practical compromise when a second support is not available, with performance between a flat dipole and a vertical.
Can I use coax without a balun on a dipole?
Technically you can transmit without a balun and the radio will work, but the antenna will not perform as designed. Without a current choke, RF current flows on the outside of the coax shield, causing the feedline to become part of the antenna. This distorts the radiation pattern, shifts the resonant frequency as you move the coax, causes RF in the shack, and raises the receive noise floor. Many operators operate without a balun for years without realizing the performance they are leaving on the table. Install a properly wound current choke and re-measure — the improvement is frequently dramatic.
Current choke guide →Why does my dipole SWR change when I move the coax?
SWR that changes when you move or reposition the coax is the classic symptom of common-mode current flowing on the outside of the coax shield. The coax is acting as part of the antenna — its routing and length become part of the resonant structure. The fix is a current choke at the antenna feedpoint with sufficient choking impedance to block common-mode current. After installing a proper choke, the SWR should become stable and independent of how the coax is routed below the feedpoint.
SWR troubleshooting guide →What wire should I use for a dipole?
For permanent HF installations, #14 AWG stranded copper-clad steel (CCS) is the best choice — it has good conductivity and significantly better tensile strength than pure copper, which stretches and sags under the tension of long spans and seasonal temperature cycling. For portable and SOTA/POTA work, #22–26 AWG magnet wire saves considerable weight. Avoid using PVC-insulated wire on dipoles without accounting for the velocity factor effect — PVC insulation slightly increases the electrical length, requiring the wire to be cut approximately 2–3% shorter than the bare-wire formula to resonate at the same frequency.
Is a dipole or a vertical better for DX?
A high dipole generally outperforms a vertical for DX on HF. A dipole at λ/2 height (65 feet on 40m) produces low-angle radiation that competes well with any vertical. A vertical's advantage is omnidirectionality in azimuth at low angles — it radiates equally in all directions simultaneously, which a dipole does not. In practice: a dipole at 50+ feet on 20m beats most low-budget verticals for actual DX contacts. A high-quality vertical with 32+ radials is competitive with a dipole at moderate height. The choice often comes down to available horizontal space versus vertical space rather than absolute performance.
What is an OCFD and is it better than a fan dipole?
An off-center-fed dipole (OCFD) uses an asymmetric feedpoint — typically 1/3 from one end of a 135-foot wire — which creates multiple resonances across HF bands from 80m through 10m. It requires a 4:1 current balun at the feedpoint. A fan dipole uses multiple parallel elements each resonant on a different band with no traps or balun needed. The OCFD is simpler physically (one wire, one feedpoint) but requires a 4:1 balun and may show higher SWR on some bands. The fan dipole is more complex to build but provides true resonant performance on each covered band with a standard 1:1 current choke. Neither is universally better — the OCFD wins on simplicity, the fan dipole wins on per-band efficiency.
OCFD build guide →