HF Baluns: The Last Two Antennas Where They Still Belong
For decades, baluns were seen as a universal fix for “balancing” antennas. In reality, almost no HF antennas are truly balanced. They may look geometrically symmetric, but electrically they are not — the ground, the feedline, and nearby objects break symmetry. That means the real workhorse for most antennas is the 1:1 current choke, not a balun with transformation.
There are only two monoband antenna families left in HF ham radio where a transformation balun still makes sense:
- Folded dipoles (monoband)
- Full-wave loops (monoband, horizontal or delta)
The keyword is monoband. On multiple bands, transformation ratios break down and the balun becomes a heater. On a single band, they can still work — though not always as the best choice.
Balun vs Feedline Transformation
For these monoband cases, you have two options:
- Current balun — A practical solution, but with ferrite loss (especially at QRO). Expect extra heat and slightly reduced efficiency.
-
Feedline transformation — A cleaner alternative:
- Use a short section of 75 Ω coax to step ~100–120 Ω loop impedance down to 50 Ω, then add a 1:1 choke.
- Feed a 300 Ω folded dipole with ladder line cut for transformation, then transition into a 1:1 choke at the rig end.
- Loss & heat: Ferrite cores in high-ratio baluns dissipate heat when used near their limits or off their design band; a correctly cut 75 Ω/ladder section is largely low-loss and runs cool.
- QRO headroom: Feedline transforms scale with coax/line voltage rating; balun core saturation and temperature rise often limit power first.
- Bandwidth (monoband focus): Both are narrow by definition; feedline sections hold their ratio precisely on the design band and don’t “drift” with heating.
- Common-mode control: Neither replaces a choke — always finish with a 1:1 current choke (ideally at 0.05–0.1 λ from the feedpoint) to keep RF off the coax.
- Practicality: Baluns are compact and convenient; feedline transforms need a short, measured section but reward you with cooler, often more efficient operation.
Both methods give you a match, but the feedline trick avoids ferrite heating and core saturation. At high power, it is the superior option.
Where Baluns Don’t Belong
- Off-center-fed dipoles (OCF) — Present ~200 Ω feedpoint impedance. The correct fix is a 4:1 unun for matching, followed by a 1:1 current choke placed 0.05–0.1 λ down the coax to block common-mode currents.
- End-fed wires (EFHW, random wires) — Electrically unbalanced. They require ununs (49:1, 9:1, etc.) and a choke.
- Yagis and verticals — Only symmetric on paper. A 1:1 choke keeps the feedline quiet and pattern clean.
Decision Table for HF Antennas
| Antenna Type | Best Solution | Alternative (less efficient) |
|---|---|---|
| Folded Dipole (monoband) | Balanced feedline transform + 1:1 choke | 4:1 Current Balun (more loss) |
| Full-Wave Loop (monoband) | 75 Ω coax + 1:1 choke | 2:1 or 4:1 Current Balun (more loss) |
| Center-Fed Dipole (multi-band) | 1:1 Current Choke | Balun not needed; adds loss |
| OCF Dipole | 4:1 Unun + 1:1 Choke (0.05–0.1 λ) | 4:1 Balun misapplied; heats at QRO |
| EFHW / Random Wire | Unun (49:1, 9:1) + Choke | Balun not applicable |
| Verticals / Yagis | 1:1 Current Choke | Balun not needed |
Short version: only monoband folded dipoles and loops can justify a balun — and even there, feedline tricks with a 1:1 choke are usually better.
Mini-FAQ
- Are baluns obsolete? — Not entirely. They still apply to monoband folded dipoles and loops.
- Why prefer feedline matching? — It avoids ferrite heating and improves efficiency at QRO.
- Can I just use a current balun? — Yes, but it’s the “lesser solution” with more loss.
- What about OCF dipoles? — Use a 4:1 unun for matching, then a 1:1 choke 0.05–0.1 λ down the line to suppress common-mode.
- What about multi-band wires? — Use a choke + tuner or unun. Baluns don’t fix imbalance there.
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