W5GI Mystery Antenna
The W5GI Mystery Antenna, published by Fred Eckert, W5GI, in QST, is a fixed 124-foot wire hybrid combining a folded, parallel-wire center section with two open tail extensions - part folded dipole, part extended double Zepp, part parallel-line stub. What earned it the "mystery" nickname is that this combination reliably presents a usable match on 80m through 10m fed directly with 50-ohm coax, often without a tuner, even though that broadband multiband behavior doesn't fall neatly out of any single simple antenna formula. This is a fixed-length compromise design, like the G5RV and ZS6BKW already on this site, not a build-to-your-frequency calculator antenna.
Three antenna concepts stacked into one wire
The center of the antenna is a folded, parallel two-wire section (closely spaced, shorted at both ends, similar in concept to a folded dipole), with two additional open-wire tail sections extending outward from each end of that folded section to reach the antenna's full 124 ft tip-to-tip length - echoing the extended-length approach of an Extended Double Zepp. That combination of a folded section plus extended tails is what gives the design its "mystery" reputation: it isn't a single clean textbook shape, it's an empirically discovered hybrid that happens to behave very well across multiple bands.
Why direct coax feed is the real selling point
Most multiband doublet-style wire antennas of similar overall length - the G5RV, the ZS6BKW, a plain doublet - need open-wire ladder line and a balanced tuner to cover multiple bands well. The W5GI's folded-plus-tails structure presents an impedance that lands close enough to 50 ohms on most HF ham bands to run straight into coax with a simple 1:1 balun, which is unusual for a fixed-length multiband wire antenna of this type and is the main reason it's worth building over a plain doublet.
- G5RV/ZS6BKW/plain doublet: ladder line + balanced tuner required for full multiband coverage.
- W5GI Mystery Antenna: direct 50-ohm coax feed, tuner often unnecessary depending on band and installation.
Why it's a fixed design, not a per-frequency calculator
Like the G5RV and ZS6BKW, this antenna's multiband behavior comes from its specific, fixed internal proportions - the folded section length, the tail lengths, and the overall 124 ft total all work together as a single published design. Scaling the whole thing to a different "design frequency" the way you would a plain dipole would change those internal proportions and isn't how this design is meant to be built or used.
Honest expectations
"Often usable without a tuner" is not the same as "always perfectly matched on every band." Expect good, usable SWR on most HF bands from this design, with the possibility that some bands or some specific installations still benefit from a modest tuner touch-up - a fair, evidence-based expectation rather than an overselling of the "mystery."
Installation options
- Flat-top between two supports: the standard install, matching the antenna's published testing configuration most closely.
- Inverted-V from a single mast: workable if you only have one high support, with the usual modest pattern and impedance shift any inverted-V configuration brings.
- Attic or stealth install: the manageable 124 ft length and direct coax feed make this a reasonable candidate for attic installation where a rotator-based beam isn't an option.
| Section | Length | Notes |
|---|---|---|
| Total length, tip to tip | 124 ft (37.8 m) | Fixed overall length - the core published spec of this design |
| Center folded (parallel-wire) section | 68 ft (20.7 m) | Two closely spaced parallel wires, shorted together at both ends of this section |
| Each open-wire tail section | 28 ft (8.5 m) | Extends from each end of the folded section out to the overall tip length |
| Parallel-wire spacing (folded section) | ~2 in (5 cm) | Consistent spacing along the full folded section |
| Feedpoint | Center of the folded section | Direct 50-ohm coax via a 1:1 current balun |
Materials for W5GI Mystery Antenna
Building the W5GI Mystery Antenna
Build the folded center section first and get its spacing consistent, then add the two tails - precision on the fixed published lengths matters more here than on a simple dipole.
Cut the folded section's two parallel wires
Cut two equal 68 ft lengths of wire for the center folded section.
Space and short the folded section
Install spacer insulators to hold the two wires about 2 in apart along the full 68 ft, and short them together with jumpers at both ends of the section.
Install the center feedpoint
At the center of the folded section, break only one of the two wires and connect the feedpoint bracket there, same principle as a folded dipole's center feed.
Cut and attach both tail sections
Cut two 28 ft tail wires and connect one to each end of the folded section, continuing outward to the antenna's full 124 ft tip-to-tip length.
Attach end insulators
Tie off the far end of each tail to an egg insulator, ready for support rope.
Install the balun and raise the antenna
Install the 1:1 current balun at the feedpoint, then hoist the antenna flat-top or as an inverted-V between supports.
Connect coax and sweep each band
Connect your feedline and sweep SWR across each HF band you plan to use, noting which bands are clean without a tuner and which benefit from one.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| One band has poor SWR while others are fine | Fault in the folded section's spacing or shorting jumpers | Recheck the folded section's spacing and both shorting jumpers first | Correct spacing/jumpers; a fault here can show up unevenly across bands rather than uniformly |
| SWR is consistently a bit high on every band | Feedpoint breaks both folded-section conductors, or a poor balun connection | Confirm the feedpoint only breaks one conductor and check the balun connection | Correct the feedpoint construction; an error here affects every band simultaneously |
| Performance doesn't match the published expectations | A section length departs from the fixed published dimensions | Double-check every section length against the published spec | Re-cut to the exact published proportions rather than assuming a small change "shouldn't matter" |
Can I scale this to a different total length for a different set of bands?
Not in the way you would a plain dipole - this is a fixed compromise design like the G5RV and ZS6BKW, where the published 124 ft total and internal section lengths work together as a package.
Do I really not need a tuner?
Often, on many bands, yes - but treat that as a strong practical advantage rather than a guarantee on every band and every installation. Keep a tuner available for touch-ups.
Why is it called a "mystery" antenna?
Because its broadband multiband performance comes from a hybrid combination of folded-dipole, extended-double-zepp, and parallel-stub concepts that doesn't reduce to one simple, obvious textbook formula - it was discovered to work well rather than derived cleanly from a single theory.
How is this different from the G5RV already on this site?
The G5RV needs ladder line and a tuner for full multiband coverage. The W5GI's folded-plus-tails structure is built specifically to allow direct 50-ohm coax feed instead.
What feed height does this need?
Standard HF wire antenna siting guidance applies - higher is generally better, with 30-50 ft being a common practical range for this length of antenna.
Who designed this antenna?
Fred Eckert, W5GI, published the design in QST, and it's remained popular since as a practical multiband wire antenna that avoids the ladder-line-and-tuner requirement of similar designs.