The W3DZZ Multi-Band Antenna has earned a reputation as one of the most reliable multiband wire antennas in amateur radio. Designed to cover five HF bands from a single feed point, it offers a simple alternative to fan dipoles or complicated matching networks. With only two tuned traps and ordinary wire, the antenna provides effective operation on 80, 40, 20, 15 and 10 meters.
What makes the design so successful is the way the traps divide the antenna electrically. On 40 meters and higher, the traps act as high-impedance barriers so that only the inner sections radiate. On 80 meters the traps behave as loading inductors, allowing the full length of the antenna to function as a shortened dipole. This clever approach gives multiband coverage without switching or tuners in most installations.
The W3DZZ Multi-Band antenna (80m-10m Trapped Dipole) stands as a masterclass in classic amateur radio engineering. First introduced by Chester L. Buchanan in the mid-20th century, this design solved a problem that still plagues hams today: how to operate across the most popular HF bands using a single, manageable piece of wire. Unlike modern multiband antennas that rely on lossy wideband transformers or complex remote tuners, the W3DZZ utilizes the elegant physics of resonant traps to provide a multiband solution that maintains high efficiency.
Basic Layout and Dimensions
The classic W3DZZ Multi-Band antenna is a centre-fed trapped dipole with a trap in each leg. From the feedpoint outward, each side consists of a 33-foot inner section, a 7MHz trap, and a 22-foot outer section. The total tip-to-tip length is therefore about 110 feet, considerably shorter than a full-size 80-meter dipole.
Fifty-ohm coax connects directly to the centre insulator. Many builders add a 1:1 current balun at this point to reduce feedline radiation and keep the SWR curve more stable, but the antenna will function without one if the installation is symmetrical.
W3DZZ Multi-Band Antenna – How the Traps Work
The traps are tuned circuits resonant close to 7.1 MHz. Each trap is made from an inductor of roughly five microhenries and a capacitor of around 100 picofarads. At its resonant frequency the trap presents a very high impedance, effectively isolating the outer wire sections when the antenna is used on 40 meters and above. On 80 meters the trap is below resonance and behaves mainly as an inductor, adding electrical length so that the full antenna can resonate on that band.
Two common construction approaches are used. The traditional method employs a coil wound on a 40mm PVC former with a discrete 100pF capacitor across it. A more modern alternative is the coaxial trap, where several turns of RG58 or similar coax are wound on a former. The coax itself provides both inductance and capacitance, producing a neat and weather-resistant assembly.
Constructing the Traps
When building the discrete LC version, most amateurs use 1.2 to 2.5mm enamelled copper wire. Ten turns on a 40mm diameter former usually give the required inductance of about 5µH. The capacitor must be a high-voltage type; silver mica or a small piece of copper laminate PCB is often used. It is important to leave a millimetre or two of clear board around the copper to prevent flashover when transmitting at higher power.
For coaxial traps, RG58 is wound directly on the former, typically around eleven turns. The ends of the antenna wire are soldered to the braid and centre conductor. This method is mechanically simpler and avoids the need to source high-voltage capacitors, although the exact number of turns may need slight adjustment depending on the coax used.
Master Craftsman Trap Construction: Coaxial vs. Discrete LC
The most critical phase of the build is the assembly of the traps. Modern builders often prefer the coaxial trap method due to its simplicity and durability. By winding 11 turns of RG-58 coaxial cable around a 40mm diameter PVC pipe, you create a self-contained capacitor and inductor. The capacitance exists between the inner conductor and the outer braid of the coax, while the coil itself provides the inductance. When wiring these, the braid from the starting end is soldered to the center conductor of the finishing end, creating the parallel circuit required for resonance.
An alternative, more traditional method involves using discrete components. This requires a 5.024 µH inductor paired with a 100 pF high-voltage capacitor. If you choose this path, the capacitor must be able to handle several thousand volts, especially if you plan on running high power, as the voltage across a resonant trap can be significant. Many builders use double-sided PCB material to etch a custom “plate” capacitor, which offers excellent weather resistance and power handling. Regardless of the method, it is vital to use an antenna analyzer to verify that each trap resonates as close to 7.1 MHz as possible before installing them in the wire.
Assembling the W3DZZ Multi-Band Antenna
Construction begins with cutting the four wire sections. Accuracy to within a few inches is adequate because final trimming will be done during tuning. The 33-foot inner wires are attached to the centre insulator, the traps are fitted to their outer ends, and the 22-foot sections complete the assembly. All joints should be soldered and then sealed carefully with self-amalgamating tape or heat-shrink tubing to keep moisture out of the traps.
The completed dipole can be erected as a flat top, inverted-V, or with slight drooping ends. Heights of eight to ten meters give good all-round performance, though the antenna will still work at lower levels with some reduction on 80 meters.
80m-10m Trapped Dipole – Tuning Procedure
Although the published dimensions usually produce a usable antenna straight away, a little adjustment pays dividends. Tuning is best started on 40 meters, as this is governed mainly by the trap resonance. If the SWR minimum is too high or low in frequency, the traps should be adjusted before altering wire lengths.
Once 40 meters is correct, attention can move to 80 meters. Here the outer 22-foot sections are trimmed equally on both sides to shift the resonance. Only small changes are needed; removing an inch from each end can move the centre frequency by several tens of kilohertz. The higher bands generally fall into place automatically, often giving multiple low-SWR points across 20, 15 and 10 meters.
W3DZZ Multi-Band Antenna – On Air Performance
In practice the W3DZZ Multi-Band antenna behaves much like separate dipoles for each band. On 40 meters it is essentially a half-wave dipole with a clean radiation pattern. On 80 meters the traps introduce a little loss compared with a full-size antenna, but the convenience of reduced length usually outweighs this. Many users report excellent DX results on 20 and 15 meters where the antenna operates on harmonic resonances.
The design handles typical amateur power levels comfortably when good components are used. Careful spacing of the capacitor and secure waterproofing are the keys to reliability, especially for stations running 100 watts or more.
Practical Installation Advice
Choose a location that keeps the ends of the antenna away from gutters, metal roofs and tree branches. Lightweight end insulators and non-conductive support rope help maintain stability in wind. Adding a choke balun at the feedpoint often cures problems with RF in the shack and makes the SWR curve less sensitive to feedline routing.
Regular inspection of the traps is worthwhile, particularly after severe weather. Any sign of moisture ingress should be dealt with immediately to avoid drift in the trap frequency.
Decades after its introduction, the W3DZZ Multi-Band Antenna remains a favourite home-brew project because it combines simplicity with real multiband capability. With a modest amount of wire, a pair of traps and an afternoon’s work, it is possible to cover most of the HF spectrum without tuners or complex switching. For newcomers and experienced operators alike, this classic trap dipole continues to deliver dependable performance from 80 through 10 meters.
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