Balanced vs Unbalanced Tuners

What Really Happens Between Your Coax and Ladder Line

Updated October 2025

The Three Typical Chains

A) rig → coax → PA → 1:1 current choke → coax → asymmetric (unbalanced) tuner → ~5 m coax → big 1:1 current choke → 600 Ω ladder line → doublet

B) rig → coax → PA → 1:1 current choke → coax → symmetric (balanced) tuner → 600 Ω ladder line → doublet

C) rig → coax → PA → 1:1 current choke → coax → asymmetric (unbalanced) tuner → 25 cm coax → big 1:1 current choke → 600 Ω ladder line → doublet

The Short Answer

On “easy” bands, the extra loss of chain A over B or C can be just a few tenths of a dB. On “ugly” bands—where the ladder line presents very high or reactive Z—adding coax and an output choke between tuner and ladder line can cost 2–4 dB, and in worst cases ≈ 4–5 dB. A balanced chain (B) avoids this penalty, while C (very short coax) limits it to a few tenths of a dB.

Numbers You Can Hang Your Hat On

ARRL/QST ran a detailed comparison with a 40 m inverted-V and ~30 m (100 ft) of balanced line. Input power was 1.5 kW:

• Balanced tuner → open-wire line (like chain B): 1325 W delivered — tuner loss ≈ 0.23 dB, line loss ≈ 0.31 dB.
• Balanced tuner → window line: 1027 W delivered — higher line loss.
• Unbalanced T-tuner + 6.1 m RG-213 + 1:1 choke → balanced line (like chain A): 397 W delivered on 14.1 MHz. Losses: −2.97 dB in coax + 156 W in the choke — > 4 dB total penalty vs balanced setup.

If your jumper is 5 m instead of 6.1 m, coax loss drops ≈ 18 %, giving ~520 W at the antenna (≈ 3 dB below balanced). Pattern remains the same: coax + choke at mismatch = real power loss.

Type C — where the balun is on the input side of an unbalanced tuner (sees 50 Ω) — shows virtually no penalty. The loss difference to a true balanced tuner is only hundredths of a dB, since no coax or choke handles a wild reactive load.

Why Chain A Can Be So Lossy

• Coax under high SWR. The short jumper “inherits” the mismatch from the ladder line. Depending on frequency and line length, voltage or current peaks inside that 5 m coax can multiply loss far beyond its matched spec.
• Output 1:1 choke heating. A current balun at the tuner output forces balance while seeing large common-mode voltages from the unbalanced network. Its resistive impedance turns that into heat—tens or hundreds of watts at high power. QST measured 156 W in one choke alone.

Practical Takeaways for Your Station

• Chain B (balanced tuner) is the low-loss baseline. All coax remains on the 50 Ω side — no balun or line segment is abused by high SWR.
• If you must run chain A:
  • Keep the coax jumper as short as possible (shorter than 5 m if you can).
  • Use a serious 1:1 current choke (Z_cm ≥ 5 kΩ across your bands) between the coax and the 600 Ω open wire.
  • Adjust ladder-line length by 5–15 % to move nasty impedances away from the tuner/choke region (read this on your tuner or use an analyzer).
• Expected extra loss with 5 m jumper:
  • “Easy” bands → ≤ 0.5 dB difference vs balanced tuner.
  • “Hard” bands → 2–4 dB typical, ≈ 5 dB possible in worst cases (as shown in QST data).

References

• R. Dean Straw, “Don’t Blow Up Your Balun,” QST, June 2015 — examples 1–6.
• AC6LA, “‘Additional Loss Due to SWR’ is in Quotes for a Reason.”
• G3TXQ, “Tuner Baluns” — why 1:1 current chokes belong here.

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