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TRIGUN-20

a tri-sector switched-beam wire antenna for 20, 15 and 10 m · a WarFi design

TRIGUN-20 is WarFi's own antenna: a tri-sector switched-beam wire antenna that gives a wire the directional gain of a beam without a rotator, a boom, or a single moving part. Three fixed elements cover three headings; a switch chooses which way you point. It was designed for a coastal Philippine station, built from native materials, and made to ride out the weather of one of the most typhoon-struck countries on earth rather than fight it. Palawan itself sits in a sheltered corner that direct typhoons rarely reach, which is good fortune, not a design assumption: the antenna is built for the whole archipelago, including operators who are not so lucky. It is documented here so anyone can build their own. The name is borrowed from a story loved since childhood, about a gunman who refuses to take a life and keeps reaching out to strangers who might yet become friends. That felt like the right spirit for an antenna: three sectors kept under watch, and a signal sent out to whoever is listening.

01Directivity without a rotator

A beam antenna concentrates your signal in one direction, which is how modest power reaches far. The usual price is a rotatable Yagi: a heavy boom of aluminium on a tower with a motor to turn it, expensive, and a liability in a typhoon. TRIGUN-20 takes a different route. Instead of one beam you turn, it uses three fixed wire beams, each aimed at a different third of the compass, and an electrical switch selects which one is live. There is nothing to rotate, nothing to seize, and nothing to tear loose in a storm.

» Three fixed elements on one frame, each favouring a 120-degree sector.

» A switch at the feed selects the heading; steering is electrical, instant, and silent.

» No rotator, no boom, no moving parts: far cheaper and far more storm-survivable.

» Covers three bands, 20, 15 and 10 metres, from the one structure.

02The structure

The elements are wire, carried on a fixed, cord-stayed hexagonal frame, with three stacked tiers so the three bands nest together rather than needing three separate antennas. It is light, it flexes in wind instead of fighting it, and it goes up on a single mast.

» Think of it as a cousin of the hexbeam, which also hangs wire elements on a frame, but with the pattern steered by switching between sectors rather than by turning the whole thing.

03Steering by sector

The three fixed beams are aimed about 120 degrees apart, so between them they cover the whole horizon. You do not turn anything: the switch simply makes one sector live, and that beam fires outward along its heading while the other two rest. Changing direction is a flick of a switch, not a slow grind of a motor, so you can follow a band as it opens one way and then another.

» The headings above are the natural DX targets from Palawan, but the frame is symmetrical: align the three sectors to whatever bearings matter most from your own location before you raise it.

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04The problem it solves

The design started from a real constraint: a 25 by 25 metre inland lot, a 15.5 metre mast, constant salt air, and the storm risk of a typhoon-prone country. A full rotatable Yagi was out, too heavy, too exposed, too costly. A plain vertical or dipole was affordable and survivable but gave no directional gain. The question was whether a wire antenna could deliver beam-like performance in chosen directions while staying light and fixed. Surveying what already existed pointed the way.

05The antennas it learned from

TRIGUN-20 borrows one good idea from each of several established designs, and leaves behind what did not fit the site.

» The hexbeam: wire elements on a light frame, compact and effective. TRIGUN keeps the wire-on-frame idea, and drops the need to rotate it.

» The Yagi beam: real directional gain from driven and parasitic elements. TRIGUN keeps the directivity, and avoids the heavy boom and the motor.

» Switched and phased arrays (the four-square vertical being the classic): steering a pattern by switching which elements are fed, no mechanical motion. This is the core insight TRIGUN is built on.

» Multiband verticals such as the Cushcraft R8: all-band coverage from one structure, but omnidirectional, so no gain. TRIGUN wanted the multiband part with gain added.

» The rotatable dipole (Cushcraft D-3) and compact commercial dipoles: simple and light, but still either omni or in need of turning.

» Put together: the hexbeam's wire-on-frame form, the Yagi's directivity, and the switched array's electrical steering, combined into a fixed, three-sector, three-band wire antenna.

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06Specifications

The figures below are the Rev F design targets. Exact dimensions and the switching scheme are in the build manual; the numbers that matter for planning are here.

» The three bands are harmonically related, so one physical structure resonates on all three with the elements scaled by frequency, which is why the tier radii fall in near-exact ratio.

07Inside one sector

Each sector is a two-element wire beam: a driven element, and a reflector about five percent longer set roughly 0.15 wavelength behind it. The reflector re-radiates with just enough delay to add to the signal out the front and cancel it off the back. That is the whole trick of a beam, done in wire. Expect what any good two-element wire beam gives: a few dB of forward gain over a dipole, and front-to-back rejection on the order of 10 to 15 dB across the part of the band you work. It is not a big stacked Yagi, and it does not try to be; it is the most gain you can hang on light wire and still trust in a storm.

» Two elements is the sweet spot for wire: most of the useful gain of a three-element Yagi, a fraction of the size and weight, and a feed impedance that is easy to match.

08The nested frame

All three bands share one cord-stayed hexagonal frame of bamboo spreaders. Three rings of wire nest on it, the largest for 20 metres and the smallest for 10, so one structure does the work of three antennas. Because 20, 15 and 10 metres are close to harmonically related, the ring radii fall in near-exact ratio, and the frame stays compact.

» The frame is a cousin of the hexbeam, which also carries wire on light spreaders. The difference is that TRIGUN is never turned: the pattern is steered by switching sectors instead.

09Switching and the feed

At the centre, where all three sectors meet, sits a small relay box. One control line runs down the mast, and whichever sector you select is the one that gets fed; the other two are left open on the frame. Because the steering is electrical, re-aiming the beam takes no time and wears nothing out.

Keep the relay box sealed against the salt air and give it a drip loop. A stuck relay is the one failure that can leave you pointed the wrong way, so it is the part to inspect first on the maintenance calendar.

10Height and DX

On 20 metres, height decides whether you work the region or the world. The ground reflection only begins reinforcing low-angle radiation, the angles DX arrives at, once the antenna is about half a wavelength up.

» A coastal, over-sea path adds a low-angle boost of a few dB in the seaward directions, which partly forgives modest height exactly where DX matters most.

11What to expect on the meter

A switched wire beam is not a laboratory antenna; the aim is a usable match across the part of each band you work, with the front-to-back and gain that make switching worthwhile. Tune each sector in turn, confirm the switch selects cleanly, and check that the pattern favours the intended heading.

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12Native materials, by hand

TRIGUN-20 was designed to be built from what a provincial operator can actually get: bamboo for the frame spreaders, ordinary wire for the elements, and hardware-store fittings, with a Philippine substitution list so nothing exotic is required. The build manual walks it in twelve illustrated steps, from preparing and sealing the bamboo to stringing and tuning the elements.

1. Prepare and weatherproof the bamboo spreaders against salt air and sun.

2. Assemble the cord-stayed hexagonal frame flat on the ground.

3. String the three nested tiers of wire elements to the scaled dimensions.

4. Wire the sector switch at the feedpoint and run the control line down the mast.

5. Raise on the single mast, then tune and verify each sector's match and heading.

13Storm doctrine and maintenance

The Philippines is one of the most typhoon-struck countries on earth, so a Philippine antenna earns its keep by surviving the season, not only by how it plays on a quiet night. Palawan is luckier than most of the country, tucked into a corner that direct hits seldom reach, but the salt air never lets up and a bad blow is never impossible, so the design still plans for the worst. A light wire antenna that flexes rides out wind that would fold an aluminium beam, and there is no rotator to seize or fail. The doctrine is simple: build it to give, keep the salt off, and check it on a calendar.

» Flex, do not resist: light wire and bamboo ride out gusts a rigid boom would not.

» No moving parts means nothing to seize, corrode, or tear loose in a storm.

» Rinse and inspect connections for salt-air corrosion on a maintenance calendar.

» Ground the mast and fit lightning protection; disconnect the feed in storms.

Antenna and mast work is the real hazard here, not the radio. Keep the whole structure well clear of power lines with room to fall, and never transmit while anyone is near it.

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14Where the project stands

The design is complete and documented through Revision F, a fifteen-page illustrated build manual with blueprint drawings, the twelve build steps, the bamboo guide, storm doctrine, a maintenance calendar, and appendices covering a 40 metre scaling and optional refinements: nested 17 and 12 metre elements, remote switching with an ESP32 and bias-tee, and a scan-while-listening mode. The station build follows the manual; as-built measurements will be added here as they are taken.

» Want the raw model to check the physics yourself? The 4nec2 geometry file will be posted alongside the manual so you can run the pattern and SWR predictions before you cut a single wire.

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