Build a 20m Moxon Rectangle Antenna
The 20 m Moxon rectangle delivers the compact directional performance that makes this design so popular — roughly 5.5 dBd forward gain, a front-to-back ratio that regularly exceeds 30 dB, and a direct 50 Ω coax feed — from a wire frame that spans just 9.5 metres wide and 3 metres deep. For any operator with a pair of supports 10 m apart, a wire Moxon on 20 m is one of the most rewarding first beam projects available.
Why 20m & Why Moxon?
Twenty metres is the flagship DX band in amateur radio — open to some part of the world almost every hour of the day during normal solar conditions and capable of worldwide contacts with modest power during solar peaks. For the operator who cannot support the mechanical complexity of a full Yagi on a rotating tower, the Moxon wire rectangle offers most of the gain and superior front-to-back performance from a lightweight wire frame that can be mounted between two trees, suspended from a single mast in an inverted-V configuration, or hung inside a large attic.
Suspended Wire Version
The lightest and simplest build. Four fibreglass spreader arms from a central hub support the wire frame. Total weight under 2 kg including feedline. Can be mounted on a light push-up mast or suspended between two supports. Excellent for portable, field day, or semi-permanent use.
Fixed Inverted Installation
The antenna frame hangs vertically between two supports — trees, poles, or building walls — with the plane of the rectangle vertical. The main sections run horizontally, the tails hang downward. Feed point at the centre of the top (driven element) section. Simple to install, no rotator needed if your target DX direction is fixed.
Rotatable on a Light Mast
A hub-and-spreader frame mounts to a short mast with a TV rotator, enabling full 360° beam heading control. The lightweight wire construction keeps wind loading low enough for rotators rated at 5–10 kg. A 20 m Moxon fits comfortably on an Alliance U-100 or equivalent light-duty rotator.
| Dim | Description | 14.025 MHz (CW) | 14.175 MHz (centre) | 14.250 MHz (SSB) |
|---|---|---|---|---|
| A | DE main section | 9.609 m | 9.505 m | 9.448 m |
| B | DE tail each side | 1.222 m | 1.209 m | 1.202 m |
| C | Gap (critical) | 0.313 m | 0.310 m | 0.308 m |
| D | REF tail each side | 1.531 m | 1.515 m | 1.506 m |
| E | REF main section | 9.541 m | 9.433 m | 9.377 m |
| Width (≈A) | — | 9.609 m | 9.505 m | 9.448 m |
| Depth (B+C+D) | — | 3.066 m | 3.034 m | 3.016 m |
Wire cut lengths: cut the driven element as a single piece of length A + 2×B = 9.505 + 2×1.209 = 11.923 m for 14.175 MHz. Mark the centre (5.963 m from each end) — this is the feed point. Cut the reflector as a single piece of E + 2×D = 9.433 + 2×1.515 = 12.463 m for 14.175 MHz. The reflector is continuous — no gap, no feed point.
20m Moxon Dimension Calculator (Cebik equations)
Materials for 20m wire Moxon (14.175 MHz design)
Complete Construction Sequence
Build the hub and spreader arms, cut and route the wire elements, install the gap spacers, then feed and raise the antenna. Allow 4–6 hours for the complete build.
Prepare the hub and spreader arms
Cut four fibreglass rod sections: two horizontal arms 1.55 m long (these extend 1.55 m from hub centre toward each corner, giving the antenna its 9.5 m total width), and two depth arms 1.55 m long (one to the front and one to the rear of the hub). Insert the rods into a PVC cross fitting and fix with epoxy or set screws. The hub becomes the mast attachment point; drill a 12 mm hole through the centre for a U-bolt clamp.
Install corner insulators
At the outer end of each horizontal arm, fit a corner insulator or fibre angle bracket. The corner insulator must hold the wire at a 90° turn — directing the DE and REF tail wires from their horizontal run down toward each other. The insulator must be non-conductive — even damp wood will detune the antenna at 14 MHz. Fix the insulator to the spreader arm with a stainless self-tapping screw and epoxy.
Cut the driven element and mark the feed point
For 14.175 MHz, cut a 11.923 m length of wire (A + 2B = 9.505 + 2 × 1.209 m). Measure exactly to the centre (5.962 m from each end) and mark with a permanent marker and a cable tie. Strip 40 mm of insulation at the centre — this is the feed point. Also strip 30 mm at each tip end. Solder a short 100 mm wire pigtail to each stripped tip end for later connection to the gap spacer.
Route and secure the driven element on the frame
Attach the DE wire to the forward depth arm at the centre (feed point), and run it along the two horizontal arms to the corners. At each corner, pass the wire through the corner insulator and turn it 90° to run down the depth arm toward the rear. Secure the wire to the spreader arms with UV-resistant cable ties every 300 mm — the wire must not sag significantly between attachment points.
Cut and route the reflector
Cut a 12.463 m length of wire (E + 2D = 9.433 + 2 × 1.515 m). The reflector runs along the rear depth arm at its centre (no feed point — this wire is continuous), then extends to the corners via the horizontal arms, then turns 90° at each corner and runs 1.515 m along the depth arm toward the driven element. At no point should the reflector touch the driven element wire or the frame hub.
Install the gap spacers and set dimension C
The gap C = 0.310 m separates the DE tip and REF tip on each side of the antenna. This is the most critical assembly step. Cut two pieces of PTFE or acrylic rod, each 35–40 mm long, drill a 3 mm hole through each piece at both ends, and thread the DE and REF tip wires into the holes. Adjust the wire lengths until the gap is exactly 310 mm (for 14.175 MHz). Verify C on both sides of the antenna is within 5 mm of identical.
Install the feed point and balun
At the centre of the DE, connect the coaxial cable. Solder the inner conductor to one wire half and the outer braid to the other. Install a 1:1 current choke immediately at the feed point — thread the feedline through an FT-140-31 toroid with 6–8 turns, or slide 6 ferrite beads over the first 100 mm of coax. Seal the entire assembly in the weatherproof ABS enclosure, secured to the forward depth arm.
Raise, orient and perform initial SWR check
Raise the antenna to its operating position — minimum 6 m for useful DX performance; 9–12 m is markedly better on 20 m. Orient the front face toward your primary operating direction. Connect a NanoVNA or antenna analyser directly at the feed point balun output with a short piece of coax. Sweep 13.5–15.0 MHz and find the SWR minimum. A correctly built Moxon will show minimum SWR of 1.1–1.3:1 within 100 kHz of the design frequency.
| Frequency (MHz) | Gain (dBd) | F/B (dB) | SWR (50 Ω) | Notes |
|---|---|---|---|---|
| 14.000 | 4.7 | 10 | 2.0:1 | CW low edge — reduced F/B |
| 14.050 | 5.0 | 18 | 1.5:1 | CW contest freq — good |
| 14.175 | 5.5 | 32 | 1.1:1 | Design frequency — peak |
| 14.225 | 5.4 | 28 | 1.2:1 | SSB DX — excellent |
| 14.275 | 5.2 | 22 | 1.4:1 | SSB — very good |
| 14.350 | 4.8 | 14 | 1.9:1 | Upper edge — acceptable |
Choosing your design frequency: for mixed CW and SSB operating, 14.175 MHz gives the best compromise. Dedicated CW operators should use 14.050 MHz as the design frequency — this shifts peak F/B to the CW portion and keeps SWR below 1.5:1 from 14.000 to 14.200 MHz. SSB DX operators can use 14.225 MHz as the design point.
Horizontal Flat-Top on a Rotator
The classic Moxon installation. The frame lies horizontally, rotating in the horizontal plane. A TV rotator rated at 5–10 kg is adequate for the lightweight wire construction. Use a non-conductive (fibreglass or PVC) mast section for the top 2 m below the antenna to prevent the mast from coupling into the radiation pattern. Weight balance matters — the hub and feedline entry should be over the mast centreline.
Fixed Horizontal Between Two Supports
The simplest permanent installation. Run a strong support rope between two trees or poles, separated by at least 10.5 m. Hang the antenna from the rope at two points — the front corner insulators attach to the support rope to maintain the full 9.5 m width. The rear of the antenna hangs freely, held in shape by the spreader arms. The antenna cannot be rotated without physical rope work.
Attic Installation
A 20 m Moxon fits inside the roof space of a house with a ridge length of at least 10 m, provided the attic ceiling is high enough for the 3 m depth dimension. Performance is reduced by proximity to the roof materials — expect resonant frequency to shift down 3–7% from the free-space calculated value, requiring the elements to be shortened slightly. Gain is reduced by 2–4 dB compared to an outdoor installation, but the noise reduction and stealth advantage in an HOA environment often outweigh the performance compromise.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| SWR minimum is at wrong frequency | Driven element length error, or asymmetric gap C | A 100 mm error in total DE length shifts resonance by approximately 100–150 kHz at 14 MHz. If one gap is significantly different from the other, the antenna is asymmetric | Re-measure the total DE wire length (A + 2B). Verify the gap C on both sides — both gaps must be equal to within 5 mm |
| SWR is 1.5–1.8:1 at design frequency — cannot improve | Gap C slightly wrong | An overly large gap pushes the feed impedance above 50 Ω; an overly small gap pushes it below 50 Ω | Experiment by temporarily reducing the gap by 20 mm on both sides and re-measuring; adjust in 10 mm increments until SWR minimum reaches 1.0–1.2:1 |
| Excellent SWR but no noticeable directional improvement | Common-mode current on the coax shield | Without a proper choke at the feed point, the coax braid becomes an asymmetric third element that disrupts the balanced two-element coupling | Install a proper 1:1 current choke and test again. Check that the reflector is not accidentally making contact with the hub or mast |
What height is needed for good DX performance on 20m?
At 14 MHz, one full wavelength is approximately 21 m. The take-off angle drops rapidly as height increases from λ/4 (5.3 m — very high angle, NVIS-like) through λ/2 (10.6 m — around 30° TOA) to 1λ (21 m — 15° TOA, excellent DX). For most suburban stations, 9–12 m is achievable and gives a 20–25° take-off angle.
How does a 20m Moxon compare to a 3-element Yagi?
A 3-element 20 m Yagi has about 7.5 dBd forward gain compared to the Moxon's 5.5 dBd — a 2 dB advantage in favour of the Yagi. However, the Moxon's 30+ dB F/B ratio far exceeds the Yagi's 20–22 dB F/B. The Moxon's 9.5 m width vs. the Yagi's 10 m element length and 7+ m boom also make the Moxon considerably more manageable mechanically.
Can I operate on 15m or 17m with a 20m Moxon?
On 17 m (18.1 MHz) the 20 m Moxon is about 1.27λ electrically long and presents high SWR — an ATU can match it but the pattern is nothing like the designed Moxon pattern. On 15 m (21 MHz) the situation is similar. For multi-band use, a separate antenna for each band is preferable.
What wire gauge should I use?
For a permanent outdoor installation, 2 mm² (14 AWG) stranded copper is the best choice — strong enough to resist sagging and stretching, fine enough to handle easily. For portable use, 1 mm² (18 AWG) saves weight. Avoid aluminium wire — it corrodes at solder joints and stretches more than copper.
How do I set up the Moxon for portable field day use?
The wire Moxon breaks down to a compact bundle. At the field site, assemble the hub and arms (5 minutes), uncoil the pre-cut wires and attach them to the frame (10 minutes), set the gap spacers (5 minutes), and raise on a pushup mast (10 minutes). Total deployment time: 30–40 minutes with one operator.
Can I build a rotatable aluminium tube version?
Yes — and it is significantly more durable for permanent use. Use 25 mm OD aluminium tube for the main A and E sections, and 19 mm tube for the B and D tails. Apply the 0.97 tube correction factor to all dimensions. The aluminium version adds approximately 6–8 kg to the assembly — verify your rotator is rated for the combined weight and wind load.