We Prefer a 4:1 UNUN for Wire Antennas Without Harmonic Relationships
Last updated: August 22, 2025.
When hams move beyond harmonic EFHWs (e.g. 80/40 or 40/20), they face impedance unpredictability. Non-harmonic bands like 60/40/30 m break the usual patterns. For slopers or flat-tops ~13–14 m long, the 4:1 UNUN is the most practical choice. Here’s why.
The Problem With Non-Harmonic Multiband Use
Harmonic EFHWs behave predictably because their impedances repeat on related bands. But non-harmonic combos like 60/40/30 m do not. Feedpoint Z can swing from 100 Ω to 1000 Ω depending on length and height. A 49:1 is tuned for ~2450 Ω at EFHW resonances — totally mismatched here. Instead, non-harmonic wires often fall in the 100–200 Ω region.
Why 4:1 UNUNs Fit the Role
- A ~14 m wire shows 100–300 Ω on 60/40/30 m
- A 4:1 UNUN steps 200 Ω → 50 Ω, inside ATU range
- Less tuner stress, better power transfer
A 9:1 UNUN expects ~450 Ω, not mid-range values. A 1:1 choke offers no transformation. Thus, the 4:1 UNUN is the sweet spot.
The Role of Counterpoises
Counterpoises stabilize Z by providing a real return path. For 60/40/30 m, use:
- ~5.3 m wire for 60 m
- ~3.5 m wire for 40 m
- ~2.6 m wire for 30 m
Attach these to the UNUN ground. This reduces soil variability and keeps matching consistent.
The Sweet Spot: 14 m Wire
A 14 m wire is non-resonant on all three bands — by design. This avoids narrow bandwidths and deep nulls. A tuner + 4:1 combo makes it smooth, especially with counterpoises and a choke further down the line.
Other workable lengths:
- 35.5 m inverted-L: excellent for 160/80/60 with counterpoises (26 m, 13.5 m, 4 m)
- 24.5 m sloper: efficient 40/30 m option with better Rr than shorter wires
As always, height, slope, and site geometry are decisive in final performance.
Conclusion
The 4:1 UNUN isn’t a compromise — it’s the right tool for non-harmonic multiband wires. For 60/40/30 on 14 m, or 160/80/60 on 35 m, it provides stable, efficient matching. Pair it with counterpoises, a choke, and a tuner, and you’ll have a compact, effective system where 49:1 EFHWs fail.
Mini-FAQ
- Why not a 49:1? — Because it expects ~2450 Ω EFHW resonance, not mid-range values.
- Why not a 9:1? — Best for very high or variable impedances, not 100–300 Ω.
- Do counterpoises matter? — Yes. They stabilize impedance and reduce soil dependency.
- Is a choke still needed? — Yes. Always add a common-mode choke further down the feedline.
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