Build a 6m Halo and 6m Moxon Antenna
The 6m band — the Magic Band — is one of amateur radio's most unpredictable and rewarding operating environments. A band where transatlantic contacts happen on a summer afternoon via sporadic-E, where F2 propagation during solar maxima produces worldwide DX, and where a simple antenna at modest height can produce contacts thousands of miles away in minutes. Two antenna designs dominate 6m fixed-station operation: the halo, a horizontally polarised omnidirectional loop that provides gain over a dipole in the horizontal plane with no pointing required; and the Moxon rectangle, a compact two-element beam that delivers genuine 4 dBd gain and excellent front-to-back ratio from a structure just 9 feet wide. This guide covers both antennas — theory, dimensions, construction from aluminium tubing, feedpoint matching, and installation for a permanent 6m station.
The 6m Halo — Horizontal Omnidirectional
The halo is a horizontally polarised loop antenna approximately one half-wave in circumference, fed at a gap in the loop with a small capacitor to cancel residual reactance. It radiates omnidirectionally in the horizontal plane — like a horizontal dipole rotated into a circle — providing coverage in all directions simultaneously without a rotator:
The 6m Moxon Rectangle — Compact Two-Element Beam
The Moxon rectangle is a bent two-element Yagi — driven element and reflector both folded into a rectangle, with the element ends facing each other across a critical gap. This end-coupling mechanism gives the Moxon its distinctive properties: wide SWR bandwidth, excellent front-to-back ratio, and a compact footprint significantly smaller than a conventional 2-element Yagi:
When to Choose the Halo vs the Moxon
Both antennas serve 6m effectively but for different operating styles:
- Choose the halo if: you want coverage in all directions without a rotator; sporadic-E openings arrive from unpredictable bearings and you cannot always be at the radio to rotate; your mast cannot support a rotator; or you want a permanently fixed antenna that works whenever a 6m opening occurs without any action required.
- Choose the Moxon if: you know your primary DX direction (Europe from North America; Japan from the western US); you have a rotator or are willing to manually repoint the antenna; you want the signal advantage of directional gain for weak-signal work or EME on 6m; or you want excellent front-to-back ratio to reject interference from one direction while working the other.
- Combined installation: many active 6m operators install both — a halo for monitoring and working unexpected openings during the day, and a Moxon or Yagi for working weak signals when the band is known to be open in a specific direction. The halo monitors passively; the Moxon is deployed when a specific opening is active.
- 6m Yagi vs Moxon: a 3-element or longer Yagi provides more gain than the Moxon (7–9 dBd vs 4 dBd) but requires a longer boom (14+ ft on 6m) and a rotator. The Moxon is often the right choice when maximum footprint is 10 ft wide and a light-duty or no rotator is available.
6m Propagation — Making the Most of Both Antennas
Understanding 6m propagation modes helps choose antenna orientation and operating strategy:
- Sporadic-E (most common): unpredictable patches of intense ionisation in the E layer, typically at 900–2,500 km distances. Openings arrive from any direction with little warning — the halo's omnidirectional coverage catches these reliably. Peak months: May–August in the Northern Hemisphere. Duration: minutes to hours.
- F2 propagation (solar maxima): worldwide DX via the F2 layer, similar to HF propagation. Occurs during high solar flux periods (sunspot maximum). Predictable paths toward the sun's reflected point. The Moxon pointed toward the target region is ideal.
- Meteor scatter: brief bursts via meteors entering the atmosphere. Digital modes (MSK144, FSK441) designed for millisecond-duration bursts. Any antenna works — the Moxon's gain helps with weak paths. Major showers: Perseids (August), Leonids (November), Geminids (December).
- EME on 6m: moonbounce on 6m requires large antenna arrays (multiple Yagis) — beyond the scope of a single halo or Moxon. However, the Moxon can be used as a single element in a small EME array.
- Tropo: less common on 6m than at VHF/UHF but occurs. Local contacts and regional paths up to 500 km possible under anticyclonic conditions.
| Parameter | 6m Halo | 6m Moxon | Notes |
|---|---|---|---|
| Design frequency | 50.150 MHz | 50.150 MHz | 6m SSB calling frequency; adjust for CW (50.090 MHz) |
| Conductor diameter | 1/2-inch aluminium | 1/2-inch aluminium | Larger conductor = broader bandwidth; always spec conductor in calculator |
| Loop/antenna diameter | 37.5 in (95.3 cm) | 9.04 ft wide × 3.68 ft deep | Moxon dimensions from AC6LA calculator |
| Feedpoint impedance | 5–15 Ω (requires matching) | ~50 Ω (direct coax feed) | Halo needs 1:4 unun; Moxon needs only 1:1 choke balun |
| Matching required | Series capacitor + 1:4 unun | 1:1 current choke balun only | Moxon's 50 Ω native match is a major practical advantage |
| Gain (dBd) | ~1–2 dBd | ~4 dBd | Moxon gain is directional; halo gain is omnidirectional |
| Front-to-back ratio | N/A (omnidirectional) | 25–35 dB | Moxon F/B is among best of any 2-element design |
| 2:1 SWR bandwidth | 400–600 kHz | Over 1 MHz | Both easily cover the entire 6m amateur band |
| Rotator needed | No | Yes (or manual pointing) | Halo's key practical advantage for unattended monitoring |
Materials for a 6m halo antenna for 50 MHz horizontal omnidirectional operation
Materials for a 6m Moxon rectangle for 50 MHz directional operation
Building the 6m Halo
The halo is the simpler of the two antennas — a single loop of aluminium tubing, bent into a circle, with a feedpoint gap and matching network. The most time-consuming part is forming a clean circular loop from aluminium tubing. Work slowly and re-check the circle's shape frequently during bending.
Calculate Loop Circumference and Cut the Tubing
The halo loop circumference is approximately 94% of a half-wave at the operating frequency — shorter than a full half-wave because the resonating capacitor provides the electrical length correction. For 50.150 MHz, start with a loop circumference of 9.4 ft (2.87 m) and plan to tune the capacitor to final resonance:
Bend the Loop into a Circle
Using the 1/2-inch tube bender, form the aluminium tubing into a circle approximately 37.5 inches in diameter. Work progressively around the tube — make gentle, overlapping bends at 10–15° intervals moving around the circumference rather than making sharp bends at a few points. A properly formed halo loop looks like a smooth circle, not a polygon.
Form the circle on a flat surface and check it frequently against a circular template — a large dinner plate (11–12 inches) used as a reference for the overall roundness. The two ends of the tubing should point toward each other, leaving a 2–3 inch gap at the feedpoint. This gap is where the tuning capacitor and matching network connect.
Build the Feedpoint and Matching Network
At the feedpoint gap, install the series tuning capacitor and impedance matching network. The halo's feedpoint impedance is very low (5–15 Ω), which requires a step-up transformer to match 50 Ω coax:
Mount Loop Horizontally and Tune Capacitor
Mount the halo loop in a horizontal plane on the mast — the loop face pointing skyward, the plane of the loop horizontal. The loop must be perfectly horizontal for omnidirectional radiation — a tilted halo has a distorted pattern with reduced gain in the low directions. Support the loop using three non-conductive ties from the loop to a central hub that attaches to the mast top.
Connect the NanoVNA and sweep 49–51 MHz. Adjust the series capacitor until the SWR minimum falls at 50.150 MHz. The SWR at resonance should be under 1.5:1 with the 1:4 unun in place. Once tuned, note the capacitor setting, then replace the variable capacitor with a fixed silver-mica or high-quality ceramic capacitor of the same value for a permanent installation:
Building the 6m Moxon Rectangle
The Moxon's critical dimension is the gap between the driven element and reflector tails — this gap controls both the feedpoint impedance match and the front-to-back ratio. Always generate dimensions from the AC6LA Moxon calculator using your exact conductor diameter before cutting any material. A 1mm error in the gap can shift SWR significantly.
Generate Dimensions from the Moxon Calculator
The Moxon rectangle's dimensions depend critically on the conductor diameter — using dimensions for a different wire gauge than your actual tubing will produce incorrect gap spacing and degraded performance. Use the AC6LA Moxon calculator (available online) with these inputs:
Cut and Bend the Driven Element
The driven element consists of two identical halves — each is an L-shaped section with a long parallel arm (dimension A) and a shorter tail (dimension B) bent at 90° toward the reflector. Cut two pieces of 1/2-inch aluminium tubing to length A + B + connection allowance. Using the tube bender, form a clean 90° bend at the A-B junction on each piece:
Cut and Bend the Reflector
The reflector is a single continuous piece of tubing bent into a U-shape. Its parallel section is the same width as the DE parallel sections (2A), and its tails (D sections) are slightly longer than the DE tails (B). The reflector connects to the driven element frame through a boom plate at the centre — it is not connected electrically to the DE:
Assemble the Frame and Set the Gap
Assemble the Moxon on a flat surface. Connect the two DE halves at the feedpoint (leave the feedpoint gap open for now — just position them). Mount the reflector parallel to the DE at the calculated depth. The DE tails and reflector tails should now face each other across the critical gap C:
Install Balun, Finalise, and Mount
Once the gap is optimised, install the 1:1 current choke balun at the driven element feedpoint. Connect the balun's balanced terminals to the two DE feedpoint ends (one terminal per half). The coax connects to the balun's unbalanced output and runs down to the mast and shack.
Secure all element joints and the gap spacers permanently. For the DE-to-boom plate connection, use stainless steel U-bolts and clamps that make a secure mechanical connection while maintaining the element geometry. Orient the Moxon with the DE facing the intended direction of maximum radiation (the front direction):
Operating Strategy — When to Use Each Antenna
Experienced 6m operators have learned that no single antenna is ideal for all 6m situations. The halo and Moxon complement each other well:
- Morning monitoring with the halo: during summer sporadic-E season (May–August), leave the receiver on the 6m calling frequency (50.150 MHz) with the halo connected. The omnidirectional coverage means any opening in any direction triggers a loud signal — no need to be at the radio constantly rotating a beam.
- Switch to Moxon when the band opens: once a sporadic-E opening is confirmed via cluster spots or hearing activity, switch to the Moxon pointed toward the active path. The 4 dBd gain makes a real difference on marginal paths during sporadic-E — the difference between hearing stations and working them.
- F2 propagation (solar maximum): F2 openings are predictable in direction — toward the equatorial region. The Moxon pointed toward Europe from North America, or toward South America or Japan, captures F2 propagation efficiently. F2 openings are longer than sporadic-E so the directional antenna is worth deploying.
- Digital modes (FT8, MSK144): the halo's omnidirectional coverage is valuable when running FT8 unattended — you work stations from all directions without needing to rotate. The Moxon is better when specifically working weak-signal stations from a known direction.
Extending to a 6m Yagi from the Moxon
If the Moxon's gain proves insufficient after some operating experience on 6m, extending to a 3-element or longer Yagi is the natural next step. On 6m the dimensions are manageable:
- 3-element Yagi on 6m: approximately 10 ft boom, 9 ft elements, 7–8 dBd gain. The step from a Moxon (4 dBd) to a 3-element Yagi (7–8 dBd) is 3–4 dB — significant for EME and weak-signal work. Requires a rotator.
- 5-element Yagi on 6m: approximately 20 ft boom, 10+ dBd gain. The standard for serious 6m DX and EME. Requires a heavy-duty rotator and substantial mast.
- Why start with the Moxon: the Moxon proves the concept of a 6m beam without the cost of a full Yagi and rotator system. Many operators find the Moxon fully adequate for their operating style and never feel the need to upgrade to a larger antenna.
- Hex beam on 6m: adding 6m wires to an existing hex beam (see the hex beam build guide) is an inexpensive upgrade that produces similar performance to the Moxon from the same hub and spreader arms. If you already have a hex beam for 20–10m, adding 6m to it costs approximately $5 in wire.
| Symptom | Antenna | Most likely cause | Fix |
|---|---|---|---|
| High SWR across entire 6m band — no minimum | Halo | Open circuit in loop; tuning capacitor open; or matching network disconnected | Check loop continuity with ohmmeter; verify capacitor is connected in series at feedpoint gap; check balun terminal connections |
| SWR minimum at wrong frequency — too high or low | Halo | Series capacitor at wrong value; loop too long or too short | Adjust variable capacitor to move resonance to 50.150 MHz; if capacitor is already at limit, trim loop (too low) or add wire stub (too high) |
| SWR at resonance above 2:1 with matching network | Halo | Matching network ratio wrong for your halo's feedpoint impedance | Measure feedpoint impedance at resonance with NanoVNA; adjust matching network ratio or try hairpin match |
| SWR good but pattern appears omnidirectional — no front-to-back | Moxon | Gap C too large or too small; or DE and reflector accidentally bonded at gap | Verify gap spacers are non-conductive (no metal); adjust gap in 5mm increments while monitoring a back-direction signal for minimum |
| SWR shifts when hand approaches the Moxon gap area | Moxon | Normal at 6m — body capacitance affects the critical gap region slightly; confirms high sensitivity of gap to nearby objects | Accept as normal; tune with final spacers installed and antenna in final position before verifying SWR |
| Moxon SWR good at ground level but shifts when raised | Moxon | Height above ground changes feedpoint impedance; normal behaviour | Re-tune gap C with antenna at final installed height; the optimum gap may differ by 3–8mm between ground level and installed height |
| Halo pattern appears to have a null in one direction | Halo | Loop not perfectly circular — flat section creates a partial dipole effect | Reshape loop carefully to restore circular geometry; verify on flat surface against circular template before installing |
Does the 6m halo really work for DX?
Yes — during sporadic-E and F2 openings, the halo's 1–2 dBd gain over a dipole combined with horizontal polarisation is fully competitive for intercontinental contacts. Many operators have worked over 100 DXCC entities on 6m using a halo as their primary antenna. The halo's key advantage for DX is its omnidirectional coverage — sporadic-E openings arrive from unpredictable directions and the halo catches them all. The 2–3 dB you sacrifice versus a beam is more than compensated by never missing an unexpected opening because the beam was pointed the wrong way.
What height should I mount the 6m halo or Moxon?
For 6m DX via sporadic-E and F2, height matters less than for VHF terrestrial work because the signals arrive from steeply inclined paths via the ionosphere — the elevation angle is 10–30° rather than near-horizontal as in VHF line-of-sight. A halo at 30 ft works almost as well as one at 60 ft for E-skip DX. For meteor scatter (near-horizontal paths) and local line-of-sight, height follows the usual rules — higher is better. A practical target: mount both antennas as high as your mast allows, but do not delay getting on 6m while waiting for a taller mast — a 6m antenna at 20 ft is fully effective for sporadic-E DX.
Can I use the Moxon without a rotator?
Yes — the Moxon can be fixed-pointed in one direction and still provide useful coverage due to its broad forward lobe (approximately 70° between 3 dB points). For a US station, a Moxon pointed northeast covers Europe and extends usefully toward the north (Canada, Arctic) and east (Atlantic openings). During a sporadic-E opening to Europe, stations within ±35° of northeast would still be heard at reduced strength. For fully omnidirectional coverage, the halo is the better choice. For semi-directional coverage with gain in the primary DX direction without a rotator, a fixed Moxon is a practical middle ground.
How do I know when 6m is open if I'm not at the radio?
Several online tools alert you to 6m openings in real time: the DX Cluster (dxcluster.com), PSK Reporter, and the VHF propagation alert services operated by various national amateur radio societies. The DX Cluster in particular provides real-time spots of stations worked via sporadic-E and F2 — searching for spots on 50 MHz with your region or call area shows immediately when the band is open toward your location. Many 6m operators set up automated alerts via email or smartphone when spots appear from target regions during the sporadic-E season (May–August in the Northern Hemisphere).
Is horizontal or vertical polarisation better on 6m?
Horizontal polarisation is strongly preferred for 6m DX on SSB and CW — it is the universal convention among 6m operators worldwide, and all SSB calling frequencies and DX activity uses horizontal polarisation. A vertically polarised antenna communicating with a horizontally polarised antenna suffers approximately 20 dB of polarisation loss — equivalent to losing 100× the transmit power. Both the halo and Moxon in this guide are horizontally polarised, matching the convention. The exception is beacon monitoring and digital modes where vertical polarisation is sometimes used for local or meteor scatter contacts — but for DX, horizontal is always correct on 6m.
What power can the 6m halo and Moxon handle?
Both antennas, built from 1/2-inch aluminium tubing, handle legal limit power (1500W in the US) without concern for conductor heating. The critical component for the halo is the series tuning capacitor — a fixed silver-mica capacitor of appropriate voltage rating handles 1500W at 6m without issue, as the voltage across the capacitor at 1500W into a resonant 50 Ω system is modest (approximately 275V peak). For the Moxon, the current choke balun must be rated for the operating power level — a balun wound on FT-240-31 cores handles 1500W at 6m comfortably. At 100W, both antennas handle power without any concern about component ratings.