Why We Still Use 600 Ω Open Wire and Not Window Line
Window line ≠ open wire line
If you're chasing low loss, high efficiency, and reliable multiband performance, only real 600 Ω open-wire line with wide spacing and smooth conductors delivers.
The Myth of “Low-Loss” 450 Ω Window Line
For years, 450 Ω window line has been promoted as a low-loss alternative to coax. And while it performs better than most coaxial cables, the marketing has exaggerated its efficiency — especially over longer runs or under high SWR.
Early ARRL Handbooks mistakenly listed optimistic loss figures, implying window line was nearly lossless. This was later corrected. In truth, most commercial window lines (using #18 stranded copper-clad steel and polyethylene insulation) show only marginally better loss than LMR-400 in real-world tests. That’s a far cry from the myth.
| Feedline Type | Loss per 30 m | Notes |
|---|---|---|
| 450 Ω window line | ≈ 1.5 – 2 dB | Polyethylene dielectric, #18 CCS |
| 600 Ω open-wire line | ≈ 0.2 – 0.3 dB | Air dielectric, #12 bare Cu |
That’s nearly 10× lower loss for real open-wire line.
Why 600 Ω Open Wire with 20 cm Spacers Wins
Lower dielectric losses:
True open-wire line uses air as the dielectric. Window line uses polyethylene, which introduces dielectric loss, especially under high RF voltage.
Lower conductor resistance:
Open-wire line typically uses #12 or #14 bare copper, not thin stranded copper-clad steel. This drastically reduces I²R losses — especially important in high SWR systems where standing-wave voltages and currents are extreme.
Wider spacing = lower capacitance = higher impedance:
Spreading the wires 20 cm apart pushes the characteristic impedance toward 600 Ω. This minimizes current for a given power level and reduces skin-effect and dielectric heating. Window line, with ≈ 12 mm spacing, runs closer to 400–450 Ω.
Negligible heating at high power:
Open-wire can handle kilowatts with practically zero temperature rise. Window line gets warm — and losses rise with temperature.
But Isn’t Window Line More Convenient?
Absolutely. And that’s why it exists. Window line is:
- Cheap
- Flexible
- Easy to mass-produce
But it’s a compromise. If you’re running:
- Long feedline runs
- Multiband antennas with high mismatch
- Legal-limit power
- Low-band operations (where every dB counts)
…then using 450 Ω window line is like driving a Ferrari with flat tires.
Practical Build: 600 Ω Line with 20 cm Spreaders
To build real open-wire line:
- Use #12 AWG bare copper wire
- Space wires 20 cm apart
- Use non-conductive spreaders every 30–50 cm (e.g., PVC, polycarbonate, Delrin, or sealed hardwood)
The result is a virtually lossless, high-power, high-efficiency line ideal for resonant or non-resonant dipoles, loops, and open-wire-fed verticals.
Final Word
The term “open-wire” gets misused. Real open-wire line is not the same as window line. One is a legacy of military and broadcast-grade engineering. The other is a compromise sold to hams in plastic bags.
If your antenna system deserves the best, don’t feed it with window dressing — feed it with the real thing.
Real open-wire line isn’t retro — it’s RF performance done right.
Mini-FAQ
- Does 600 Ω line need a tuner? — Only if the antenna isn’t resonant. A monoband dipole at resonance doesn’t need one.
- Can I run 600 Ω line through walls? — Yes, with proper stand-offs or ceramic feed-throughs. Keep spacing consistent.
- Can I use insulated wire? — You can, but it lowers impedance and increases dielectric loss. Bare copper is best.
- What about rain and snow? — Moisture slightly changes impedance but rarely adds measurable loss.
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