Build an 80m Full-Wave Loop Antenna
An 80m full-wave loop is 280 feet of wire formed into a closed loop — a large antenna by any measure, but one that rewards the installation effort with performance no other 80m wire antenna can match at the same height. The loop's full-wavelength circumference gives approximately 2 dB gain over a dipole on 80m, excellent noise rejection on receive, and with a ladder line feed, complete multi-band coverage from 80m through 10m from a single wire structure. This guide covers every configuration option for a large loop on a real property, the specific support considerations for 280 feet of wire, and the complete build and tuning process.
Why 280 Feet and Why a Loop?
A full-wave loop resonates when its circumference equals one complete wavelength at the operating frequency. At 3.600 MHz (80m), one wavelength is approximately 272 feet in free space — in practice, antenna wire has a velocity factor slightly below 1.0, so the actual wire length needed is approximately 275–285 feet depending on wire diameter and installation height.
The loop's advantage over a dipole at the same height is approximately 1.8–2.2 dBd of gain in the favored direction, combined with noticeably lower noise pickup on receive — a real and audible improvement in operating practice on a noisy band like 80m.
Choosing the Loop Shape for Your Property
A 280-foot loop can take any closed shape — the shape determines the support requirements and, to a lesser extent, the radiation pattern. The most common configurations:
- Square loop (sky loop): four equal sides of 70 feet each, all at the same height. Requires four support points at 30+ feet. Most omnidirectional pattern. Most common for large rural properties. Horizontal polarization when mounted horizontally.
- Rectangular loop: two long sides and two short sides. Useful when the available horizontal space is asymmetric — a lot that is 100 feet long but only 40 feet wide can accommodate a 100×40-foot rectangle (280 ft perimeter). Somewhat directional broadside to the long sides.
- Delta loop (triangular): one tall apex support plus two lower base anchors. The most practical for properties with one tall tree or mast. The apex needs to be at least 60–65 feet for the loop to clear the ground adequately. Produces mixed horizontal and vertical polarization.
- Irregular/conforming shape: the loop can follow property boundaries, fence lines, or tree locations — any closed shape works. Performance depends on the specific geometry but is typically within 1–2 dB of a regular shape.
For most operators: a rectangular or square loop following property boundaries is the most practical. The loop does not need to be a perfect geometric shape to work well.
| Configuration | Shape | Support points needed | Min. height required | Polarization | Best for |
|---|---|---|---|---|---|
| Horizontal square | 70 × 70 ft | 4 corners at same height | 30 ft min, 50 ft preferred | Horizontal | NVIS regional; omnidirectional; large rural lots |
| Horizontal rectangle | Any ratio, 280 ft perimeter | 4 corners at same height | 25 ft min | Horizontal | Long narrow lots; follows fence lines |
| Delta (apex up) | Triangle, apex high | 1 apex (60+ ft) + 2 base anchors | 60 ft apex ideal | Mixed H+V | Single tall tree; DX + regional compromise |
| Vertical delta | Triangle, upright plane | 2 tall supports (60+ ft) or 1 very tall | 70 ft for full vertical | Vertical (dominant) | Best DX on 80m; hardest to install |
| Irregular perimeter | Follows property boundary | As many trees/posts as needed | 8 ft min clearance | Mixed | Odd-shaped lots; fence-line installation |
80m Loop Calculator
This design has published dimensions for more than one band, or this page has no dedicated dimensions table this script could confidently locate. The default shown below is the most frequently cited frequency on the whole page -- verify it before trusting the result.
Where to Feed the 80m Loop
The feedpoint location on the loop determines the feedpoint impedance and the polarization of radiation on 80m. On the harmonics (40m, 20m, etc.), the feedpoint impedance and pattern both change significantly from the fundamental. For a coax-fed loop targeting primarily 80m operation:
- Corner feed (square or rectangular loop): feedpoint at one corner. Impedance approximately 100–130Ω on 80m. Requires 2:1 or 4:1 balun to match 50Ω coax. Simplest to access for installation and maintenance.
- Side-center feed: feedpoint at the mid-point of one side. Impedance approximately 50–70Ω on 80m — much easier to match. Requires 1:1 current choke to 50Ω. Slightly harder to access on a side mid-span.
- Ladder line from any position: the best choice for all-band operation. Connect ladder line at any convenient point on the loop, route to a balanced tuner in the shack. The tuner handles all HF bands. This eliminates the impedance matching issue entirely and gives maximum operating flexibility.
For operators who primarily want 80m operation with the option of other bands: side-center feed to a 1:1 current choke gives the cleanest 80m match. For all-band operators: ladder line feed is the clear winner.
80m Loop Multi-Band Coverage
Fed with 450Ω ladder line to a balanced tuner, an 80m full-wave loop covers every HF band from 80m through 10m. The loop wire is resonant or near-resonant at multiple amateur bands as harmonics of the 80m fundamental:
The gain on harmonic bands can be significantly higher than on the fundamental. A full-wave loop at the 4th harmonic (20m) produces approximately 3–4 dBd of gain in specific directions — better DX performance than a simple dipole by a noticeable margin.
Complete materials for an 80m full-wave rectangular loop
Building the 80m Full-Wave Loop
Plan the geometry first, then build the feedpoint, cut the wire, raise all four corners, and tune. Allow a full day — the 280-foot wire and four support points make this the most installation-intensive guide in this series.
Survey the Property and Plan the Rectangle
Walk the full perimeter of the planned loop installation with a measuring tape. The 280-foot loop can be any rectangle — choose dimensions that fit the available space and maximizes the corner heights. For a typical suburban lot 100 feet deep and 60 feet wide, a 100×40-foot rectangle (280 ft perimeter) is a natural fit and uses the full lot depth.
Identify a tree, post, or mast at each planned corner. Mark each corner location with a stake or marker. Measure the actual perimeter by walking each side — real property corners are rarely exactly where a map suggests, and the actual distances may require adjusting the rectangle dimensions.
Plan Corner Heights and Mid-Span Supports
On a horizontal 80m loop, height is everything for DX performance. The average height of the loop determines the takeoff angle — aim for the highest consistent height possible across all four sides. A loop where two corners are at 50 feet and two corners are at 15 feet will sag severely on the low sides, reducing average height significantly. Better to have all four corners at 30 feet consistently than two high and two low.
For sides longer than 50 feet, plan a mid-span support at the wire mid-point to prevent excessive sag. The wire weight for 70 feet of #14 CCS wire is approximately 350 grams — manageable with moderate rope tension at the corners, but a mid-span support reduces catenary sag significantly on long sides:
Build the Feedpoint Assembly
The feedpoint assembly connects the loop wire to the ladder line. For a ladder line feed at the mid-point of one side of the rectangle:
Use a commercial ladder line feedpoint insulator, or fabricate from a 3-inch section of 1/4" polycarbonate rod with two small stainless eyebolts. The two conductors of the ladder line connect to the two eyebolts — one conductor to each side of the point where the loop wire is interrupted for the feed connection.
The loop wire is cut at the feed point: the two wire ends at the feed cut connect — one end to one ladder line conductor, the other end to the other conductor. The ladder line then runs down and away from the loop toward the shack, maintaining at least 6 inches clearance from any metal structure along its route.
Cut and Lay Out the Wire
Cut one continuous piece of wire to 287.6 feet (for a 3.600 MHz target with 3% trimming room). This is a substantial amount of wire — the full spool will be nearly empty after cutting. Lay the wire out on the ground in the shape of the planned loop — use the survey stakes at each corner as guides. Verify the perimeter by walking each side with the tape measure while the wire is laid out. This is the last opportunity to make major adjustments before the wire is in the air.
Install corner insulators at each of the four rectangle corners: cut the wire at each corner, thread both ends through the insulator, wrap each end back 4 inches, wrap 5 times, and solder. Leave both wire ends of the feedpoint gap disconnected until the feedpoint assembly is attached.
Get Support Ropes Over All Four Corner Supports
Before raising any wire, get a support rope over each of the four corner trees or posts. Use a throw weight and line for trees — throw over a branch at the target height, pull a Dacron support rope through, and leave the rope hanging at the corner location with enough length to lower and raise the corner wire as needed during installation.
Work all four corners before raising any wire. It is much easier to get throw lines into four trees when you are not simultaneously managing a heavy wire loop. Once all four support ropes are in place, the actual wire raising is quick — one person at each corner simply pulls the wire up to height and secures the rope.
Raise the Loop — All Four Corners
Attach each corner insulator to its corner support rope. Begin raising all four corners simultaneously — a helper at each corner is ideal, or raise two corners first to mid-height, then the other two, then all to full height. Keep the wire from dragging through vegetation as it rises — wire dragging through branches picks up debris and can snag badly.
Once all four corners are at target height, adjust tension on each corner rope until the loop wire is visible and reasonably taut on all four sides. Some sag on long sides is normal — correct with mid-span supports on sides over 60 feet if needed. The loop should form a rough rectangle visible from the center of the installation area.
Connect the Feedpoint and Route the Ladder Line
Connect both wire ends at the feedpoint gap to the feedpoint assembly terminals — one wire end to each terminal. Verify both connections are mechanically secure. Connect the ladder line at the feedpoint assembly — one conductor to each terminal.
Route the ladder line from the feedpoint down toward the shack. The ladder line must maintain 6 inches clearance from all metal surfaces including gutters, downspouts, and metal-framed windows. Use ladder line standoff insulators where the line must pass close to the building. Allow the ladder line to hang freely in the air for as much of its run as possible — the more of the run that is free in air, the lower the feedline loss and the more predictable the impedance transformation.
At the building wall, use a ladder line feedthrough insulator — a ceramic or polycarbonate piece specifically designed for balanced line wall penetration. Never pull ladder line through a standard coax feedthrough — the close spacing of the two conductors against a conductive or damp wall section changes the line's characteristic impedance and affects performance.
Install the Balanced Tuner and Verify Connection
Connect the ladder line to the balanced tuner inside the shack. The tuner must be a true balanced (differential) tuner — a Z-match, Johnson Matchbox, MFJ-974, or similar. A standard unbalanced antenna tuner connected to ladder line via a 1:1 balun is a compromise that works but a true balanced tuner is significantly better.
Before transmitting, verify the ladder line connection is correct: with the radio connected and no power applied, sweep the 80m band with the NanoVNA connected at the radio-side of the tuner. The tuner should be able to find a match (SWR below 1.5:1) on 80m with some tuner adjustment. If the tuner cannot find any match, check the ladder line continuity and feedpoint connections.
Verify 80m Resonance with NanoVNA
Temporarily bypass the balanced tuner and connect the NanoVNA directly across the ladder line terminals to measure the bare feedpoint impedance. Sweep 3.3 to 4.1 MHz. Look for the resonance frequency — where the reactance crosses zero on the Smith chart or where the loop's natural impedance shows its characteristic pattern.
With wire cut to 287.6 feet for 3.600 MHz, expect resonance around 3.55–3.65 MHz before trimming. On 80m the loop's SWR curve at resonance into its natural impedance (approximately 100Ω at a corner or 50–70Ω at a side center) should show a distinct minimum. Note the resonant frequency and the impedance at resonance.
Trim to Target Frequency
Trim the loop wire to raise 80m resonance to the target frequency. Since trimming one point changes the total loop perimeter, lower one side of the loop at a convenient access point, cut equal amounts from each wire end at that point, re-join, re-raise, and re-measure. For an 80m full-wave loop:
Trim conservatively — the loop resonance is sensitive to ground conditions on 80m, and what seems like an off-resonance issue in very dry conditions may be perfectly resonant in normal conditions. Measure on at least two different days before making large trim decisions.
Verify All-Band Coverage Through the Tuner
With 80m resonance confirmed, verify that the balanced tuner can find acceptable matches on every HF band. Set the tuner to a mid-band setting on each band and adjust for minimum SWR at the radio. A properly installed 80m full-wave loop with a good balanced tuner should achieve below 1.5:1 SWR on every band from 80m through 10m:
- 80m: tuner required — loop natural impedance needs matching to radio
- 40m: tuner typically easy to match — loop at 2λ presents manageable impedance
- 20m: tuner required — impedance at 4λ is variable but matchable
- 17m, 15m, 12m, 10m: all matchable with tuner — higher harmonic bands
- 30m: may be challenging but achievable — near-harmonic at 3λ
If the tuner cannot find a match on one or more bands, check the ladder line length — certain ladder line lengths create impedances that push outside the tuner's matching range. Adding or removing a foot or two of ladder line often resolves this.
Weatherproof, Inspect, and Document
Apply self-amalgamating tape to the feedpoint connections where the ladder line meets the loop wire. Wrap each conductor connection individually, then wrap the entire feedpoint assembly with an outer layer. Apply PVC tape for UV protection. The feedpoint is at height and may be difficult to access after installation — thorough initial weatherproofing reduces the need for early maintenance.
Inspect each corner insulator connection visually from the ground — look for wire kinks at the insulator wrap points and verify each corner rope is properly secured. Check mid-span supports if installed.
Document the installation: loop dimensions (each side length measured on the ground), corner heights (approximate), feedpoint location and ladder line run length, resonant frequency on 80m, and the tuner settings on each primary band. Photograph each corner and the feedpoint from the ground. Plan inspection of corner rope conditions every 6 months — the multiple rope-over-branch contact points on an 80m loop are the most common maintenance items.
80m Loop vs 80m Dipole — Real-World Difference
The 2 dBd theoretical gain of a full-wave loop over a dipole at the same height is real and audible in on-air operation. In practical terms:
- On 80m receive, the loop is noticeably quieter than a dipole — signals are stronger relative to noise because the loop's radiation resistance is higher and it couples less to near-field local noise sources
- On 80m transmit, the 2 dBd gain is equivalent to increasing transmitter power by 60% — from 100W to 160W effective. Over a full DX pileup season, this margin matters
- The loop covers the full 80m band with the tuner without the sharp bandwidth limitation of a resonant dipole or EFHW — operationally more convenient for operators who work both CW and SSB ends of the band
- On 40m (2nd harmonic), the loop performs comparably to a full-size dipole with some additional directional gain depending on orientation — a useful free bonus from the installation
- The primary trade-off is complexity: the 80m loop requires significantly more installation effort, more wire, and more support points than an 80m dipole
The 80m Loop on 160m
A 280-foot wire loop is approximately half a wavelength on 160m (530 feet for a full wave). Operating the loop on 160m requires a tuner and results in moderate efficiency, but it is a practical option for operators who want some 160m capability without a dedicated antenna:
- The loop presents a capacitive impedance on 160m — the tuner must provide inductance to resonate it
- A good balanced tuner with sufficient inductance range can match the 80m loop for 160m operation
- Efficiency on 160m is lower than on 80m — estimate 30–50% of the input power actually radiated, with the rest lost to ground and tuner
- For casual 160m contacts and listening, the 80m loop on 160m is entirely adequate
- For serious 160m DX, a dedicated 160m antenna is necessary — but the 80m loop gets you on the band without additional hardware
- The loop's receive noise characteristic on 160m is still better than a dipole of the same height — a genuine advantage for listening to DX on a noisy band
Dealing with Property Constraints
An 80m full-wave loop requires 280 feet of wire perimeter — the single largest constraint for most residential installations. Practical solutions for common problems:
- Lot too small for a full square: use a very elongated rectangle — a 120×20-foot rectangle fits many suburban lots and provides a full 280-foot perimeter. The elongated shape biases radiation broadside to the long dimension.
- Only two tall trees, not four: use an inverted-U shape (two tall sides + a low bottom wire) — the low bottom wire can run at 8 feet height along a fence. The top and two sides run between the tall trees.
- One tall tree only: use a delta loop configuration with the apex at the tall tree. The 80m delta loop needs an apex at approximately 90 feet for a balanced equilateral triangle — or a very tall narrow triangle if 90 feet is not achievable.
- Fence line installation: run the loop along fence lines at 8–10 feet height. The low height limits DX performance but provides excellent NVIS regional 80m coverage and full multi-band tuner coverage of all other bands.
Noise Performance — The 80m Loop's Hidden Advantage
The 80m full-wave loop is consistently reported by operators to have lower noise pickup than an 80m dipole at the same height. This is particularly noticeable in suburban and urban environments where local interference (power line noise, VDSL, LED drivers, solar inverters) creates a noise floor that limits the ability to copy weak signals:
- The loop's closed, balanced structure provides some inherent common-mode noise rejection — noise that appears equally on both conductors at the feedpoint partially cancels
- The loop's higher radiation resistance compared to a dipole means a lower noise figure — the ratio of signal to noise is inherently better
- Many operators in suburban environments report being able to copy signals on the 80m loop that are completely buried in noise on a dipole at the same height
- This noise advantage applies to receive only — on transmit, the loop's 2 dBd gain advantage is the primary improvement
- For 80m contesting and DX work, the combination of gain and noise rejection makes the full-wave loop one of the most effective 80m wire antennas available
How high does the 80m loop need to be?
For NVIS regional 80m coverage (500–1500 miles), a height of 20–30 feet for the full loop is adequate — lower height actually helps for NVIS by increasing the upward radiation angle. For DX performance on 80m, the average loop height should be 50 feet or more. An 80m loop with corners at 40 feet represents a good compromise — genuinely useful for both regional and DX contacts. The single most important height recommendation: get all four corners to similar heights. An uneven loop with two corners at 50 feet and two at 20 feet performs worse than a level loop at 35 feet.
Can I use a standard shack ATU instead of a balanced tuner?
Technically yes, with a 1:1 current balun between the ATU and the ladder line — but a true balanced tuner is significantly better. A standard ATU feeding balanced line through a balun works but the balun's voltage and current stress at some impedances can cause balun core saturation and added loss. A true balanced tuner handles any impedance from the ladder line without stressing a balun. For 100W operation on all bands, a quality balanced tuner is worth the investment. For QRP or occasional use, a standard ATU with a good 1:1 current balun works adequately.
Does the loop shape matter — square vs rectangle vs irregular?
Shape matters less than total wire length and average height. A square loop and an elongated rectangle of the same perimeter perform within 1–2 dB of each other at the same height. An irregular loop that follows a property boundary performs comparably to a regular rectangle of the same perimeter. The primary shape effect is on the radiation pattern — a square loop has a more omnidirectional pattern while a very elongated rectangle has more gain broadside to the long dimension. For most operators, fitting the loop to the available space while maximizing perimeter and height matters far more than achieving a specific geometric shape.
Why does my balanced tuner struggle to match on some bands?
The impedance presented at the shack end of the ladder line depends on the ladder line length as well as the antenna's feedpoint impedance. At certain ladder line lengths, the impedance transformation through the line can produce very high or very low impedances that push outside the tuner's matching range. Adding or removing 6–12 inches of ladder line at the shack entry shifts the electrical length of the line and changes the impedance presented to the tuner — often resolving the matching issue. Similarly, the balanced tuner's inductance range must be adequate for the lowest frequencies (80m) where inductance requirements are highest. Some basic balanced tuner designs have insufficient inductance range for 80m full power operation.
How do I handle the 80m loop in high wind and ice loading?
An 80m loop in high wind generates significant aerodynamic force on each wire side — particularly the sides that are perpendicular to the wind direction. Use 3/16" Dacron rope at each corner rather than thinner rope, and inspect the rope-over-branch contact points after each major storm. Ice loading (in northern climates) adds weight to the horizontal wire sections that can exceed the breaking strength of thin rope — upgrade corner ropes to 1/4" Dacron in areas where ice loading is common. Mid-span support ropes are particularly valuable in high-wind or icy conditions since they prevent the wire from swinging and chafing against branches. Accept that some wire maintenance will be needed after severe weather — plan by storing spare wire and connectors.
Is an 80m full-wave loop worth the extra installation effort vs a simple dipole?
For serious 80m operators, yes — the combination of 2 dBd gain plus improved receive noise makes a real operating difference. For casual 80m operation, the extra effort probably is not justified and an 80m dipole at the same height is much simpler. The sweet spot: operators who regularly work 80m DX, participate in 80m contests, or are active in 80m emergency communications networks will find the loop's performance advantage genuinely useful. Operators who only occasionally use 80m for regional contacts will not notice enough difference from the additional installation complexity to justify it. Honest self-assessment of 80m operating intensity should drive the decision.