In the era of modern amateur radio, dominated by antenna modeling programs and mammoth dynamic beams, there is a gem from the past that deserves to be dusted off: the G3LZR Tribander.
It’s clear that this isn’t an antenna for those seeking “turnkey” perfection, but for those who love challenge and experimentation.
Developed in the 1970s by the genius of Fred Caton (VK2ABQ) and perfected by his friend Ted Womack (G3LZR), this unique tribander defies conventional element spacing. While a standard Yagi can occupy several meters of space, the G3LZR, as evidenced by its shape, folds in on itself using a unique concept: Voltage Feedback.
If you’re looking to experiment on a budget, have a couple of fishing rods, and are curious to see how capacitive coupling between the tips can create a cardioid pattern, read on.
Here’s how high-voltage physics can help you DX with recycled materials.
The Theory: “Voltage Feedback” and the Cardioid Pattern
Unlike a standard Yagi-Uda which employs inductive coupling over a boom length of several meters, the VK2ABQ is a closed-geometry parasitic array. It has a driven element, and a reflector loop bent into a square shape, supported by an X-frame.
The conceptual advance of G3LZR‘s implementation is in the element tips. In a dipole, the tips are the points of maximum voltage (High-Z). G3LZR set these high-voltage tips to face each other, separated by only a few centimeters of insulator. He called this phenomenon “Voltage Feedback“.
Formally, this is in essence a critical capacitive coupling. By placing the voltage nodes of the driver and the reflector close to each other, the antenna uses the electric field (E-field) to induce current in the reflector.
This “feedback” then causes the structure to have a phase shift (approximating the 90 degree phase shift of a Yagi Uda), which creates a cardioid distribution pattern.
The end result is a small-beam (the turning radius being only 12 ft (3.5m))
The Original Construction
G3LZR’s 1980 specifications called for materials that were cheap and easily attainable : bamboo canes for spreaders, coat buttons or small Perspex scraps for insulators, and 75 ohm TV coax.
Is this still feasible? Yes, but with a caveat. If you are a beginner looking for a temporary, portable antenna for a weekend of Field Day or camping (POTA/SOTA), then the original is perfect. Bamboo is light, as are the buttons, and a few yards of coax. In a temporary environment, the deterioration of the materials doesn’t matter : tape the wires to the canes, hoist the apex in the air 20ft off the ground, and enjoy 20 m beamforming for the price of a sandwich.
The Modern Upgrade: Built to Last
However, if you are planning on putting this on the roof half-permanently, then the materials used in the original projects will cause issues. As you know, Bamboo is hygroscopic, it absorbs water which will detune the antenna when out in the elements. The “coat button” insulators can arc-trace under high power or if dirty.
To make a G3LZR design that will survive the 21st century, follow these modern design protocols:
The Spreaders : Fiberglass is King
Discard the bamboo. Use telescoping fiberglass fishing poles or dedicated spreader kits (such as those designed for a Quad or Moxon). Fiberglass is corrosion-proof, and RF-transparent. It means that while water may slow down your rain delay a little, the structure of the antenna does not change, keeping the high-Q reflector resonant as designed.
The Wires : Stability over Mass
G3LZR used standard plastic-covered hookup wire. Today, use UV resistant Kevlar-cored wire. (or Poly-Stealth). This prevents the wire from stretching over time. In a high-Q system of this nature, a stretch of just 2cm can cause the resonance to shift out of the band.
The “Voltage Feedback” Gap : High-Quality Dielectrics
The gap between the elements tips is the heart of the antenna. Don’t use a button, use a Delrin spacer (or other high quality Polycarbonate or Delrin) to isolate the element tips. The distance must be permanently fixed; if a gust of wind causes the elements to compress, the SWR will weathervane.
The Feed System : Baluns are Mandatory
The original iteration often ignored the balun. Today, with the advent of switching power supply powered homes, a 1:1 Current Balun (Choke) at the feedpoint is a must. It stops the coax braid from becoming part of the antenna, preventing the back-lobe nulls from being “eaten” by common mode currents.
A Bridge Between Yesterday and Today
Let’s be clear: the G3LZR will never replace your Hexbeam or even your 3-element Yagi. As you’ve probably figured out, this is essentially a high-Q system, and therefore sensitive to humidity, with a bandwidth that often requires some patience during calibration. But that’s where the fun is, right?
Building a “modernized” version today using fiberglass and Delrin insulators isn’t just about assembling a smaller antenna, it’s about participating in a lineage of empirical engineering that puts genius before money. It also means retracing an experimental process that has dominated magazines in both hemispheres for nearly two decades, and which gave birth to the Moxon, HexBeam or Cobwebb antennas we all know today.
However this could be the ideal antenna for a memorable Field Day or for those who live in an apartment building and want to demonstrate that a “low profile” doesn’t mean sacrificing your ability to be heard, perhaps by setting it up specifically for that contest you’d love to participate in, but don’t have a “fixed” antenna.
After all, the true spirit of amateur radio isn’t about buying DX, but about snatching it from the airwaves with a piece of wire and a good idea.
FAQ
The Cobwebb antenna is the most famous, invente by G3TPW are basically folded dipoles mounted on a cross-shape support. The modern Hexbeam is the true successor to the “compact wire directive.” It uses a 6-arm structure shaped like an upside-down umbrella.
The Moxon is the “spiritual daughter” of folded element antennas. It has replaced the VK2ABQ in the hearts of builders because it is easier to model in simulation software and much more robust in maintaining tuning.
This antenna fell victim to technological and market evolution for three main reasons:
The advent of the Moxon Rectangle: The Moxon solved the same problem (reducing the size of a Yagi by bending the tips) but more efficiently.
Calibration Difficulty: Calibrating this antenna requires patience.
Mechanical Fragility: The “X” structure with perimeter wires is subject to mechanical stress and stretching that affect resonance.