Why Voltage Transformers (UNUNs) Are More Efficient Than Baluns for Real HF Antennas
One of the recurring myths we hear is that “balun transformers are inefficient.” The truth is more subtle: voltage-driven transformers (UNUNs) are efficient, while balun transformers waste energy when applied to HF antennas that are only balanced geometrically — not electrically.
Geometric vs. Electrical Symmetry
On paper, antennas like dipoles, loops, and even quads look “balanced.” But when you add ground, feedline routing, and real-world surroundings, that balance vanishes. The system is unbalanced by nature — even if the geometry looks perfect.
A balun transformer assumes symmetry that simply isn’t there. It wastes energy trying to enforce equal and opposite currents. In contrast, a UNUN accepts the unbalanced reality and simply transforms impedance efficiently.
Commercial Practice: Why UNUNs Dominate
- Mini-Circuits: Their massive catalog of RF transformers is overwhelmingly UNUNs. They only offer a handful of true baluns, mainly for IC differential ports. For antenna and wideband use, it’s UNUNs all the way.
- Broadcast industry: AM and shortwave transmitters feed antennas with tapped coils and auto-transformers (UNUN-style networks). Curtain arrays and rhombics, which look symmetrical, are still fed this way — with separate chokes to control common-mode current.
- RF modules: Cellular, WiFi, GNSS, and SDR front-ends use UNUN matching transformers into antennas. True baluns are reserved only for I/Q or differential IC interfaces.
- Test equipment: Rohde & Schwarz and others nearly always couple probes and front-ends through UNUN-style transformers, not baluns.
Scientific Support
Engineers like Rudy Severns (N6LF) have demonstrated that “balanced” antennas in real soil are never electrically balanced, and that forcing balance creates extra loss. Tom Rauch (W8JI) has long explained that voltage baluns are lossy in practice — but the underlying truth is that most HF antennas aren’t balanced enough for a balun to make sense in the first place.
Typical insertion loss values at HF:
- UNUN (voltage transformer): 0.05–0.2 dB across HF bands.
- Current balun on “balanced” load: 0.1–0.3 dB (good case).
- Balun on real HF dipole or loop: often 1–2 dB wasted as heating and feedline common-mode current.
That’s up to 25–40% of your TX power lost — and on RX it means a permanently higher noise floor.
The RF.Guru Approach
Our HF matching products follow this industry-proven strategy:
- Use a UNUN for efficient impedance transformation.
- Add a dedicated choke for common-mode suppression.
- Stop wasting power on a balun transformer that assumes a perfect symmetry which your antenna does not have.
Conclusion
When someone claims “baluns are inefficient,” the correct answer is: yes, because HF antennas aren’t electrically balanced to begin with. The efficient solution is a UNUN for transformation, plus a choke for noise and common-mode control. That’s why commercial industry, from Mini-Circuits to broadcasters, has been doing it this way for decades.
Mini-FAQ
- So are all baluns bad? — Not always. On true monoband, center-fed antennas with controlled surroundings, a current balun can work fine. But they’re rare outside textbooks.
- Why don’t I see “baluns” in RF catalogs? — Because industry favors UNUNs; baluns only appear for chip-level differential ports or test jigs.
- How do I keep my coax quiet? — Use a proper 1:1 choke after the UNUN. That kills common-mode current without wasting power.
Questions or experiences to share? Feel free to contact RF.Guru.
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