The Open Wire Balanced Feedline: The Forgotten Ultra-Low Loss Champion
Why 600 Ω Open-Wire Line Still Reigns Supreme for Multiband HF Antennas
When it comes to feeding multiband HF antennas like doublets, dipoles, and loops, few solutions offer the performance and flexibility of 600-ohm open-wire line. Let’s break down why this classic feedline still outperforms modern alternatives like 300-ohm twin-lead and even coaxial cable, especially in demanding HF applications.
Impedance Matching and SWR Tolerance
Multiband antennas rarely present a perfect match at all frequencies. Coaxial cable, with its fixed 50 Ω characteristic impedance, suffers significant loss when SWR increases — especially at high frequencies and long runs.
In contrast, 600 Ω open-wire is extremely forgiving. Its low loss per meter and high voltage handling mean it can tolerate high SWR without turning into a dummy load. It’s ideal for use with a transmatch (tuner).
Low Loss Even Under Mismatch
Technically speaking, power loss in feedlines is proportional to I²R losses and dielectric losses. Coax has a lossy dielectric and carries current on both the inner and outer conductors — this becomes problematic when mismatch forces current imbalance.
Twin-lead uses a foamed dielectric that degrades in wet or humid conditions. Its higher loss per meter, smaller spacing, and plastic jacket mean it performs poorly when wet, bends too easily, and detunes when run near metal.
600 Ω open-wire line, by comparison:
- Has very wide spacing (12–14 cm)
- Uses air as the dielectric — the lowest loss possible
- Has negligible loss, even with high mismatch
- Maintains impedance stability regardless of moisture or bending
RF Behavior Near Objects
Balanced lines like twin-lead and open-wire are sensitive to nearby objects — but twin-lead is far worse. Its narrow conductor spacing allows common-mode pickup and coupling to nearby metal, causing RF distortion and increased loss.
600-ohm line, with its wider spacing and improved field cancellation, suffers much less from this effect.
Build Quality and Power Handling
TV twin-lead was never designed for high-power RF. It was a consumer-grade product for VHF/UHF television and cannot handle kilowatts of HF power, nor survive UV exposure, moisture, or physical stress over years.
By contrast, properly built open-wire line:
- Handles high power with ease (1–5 kW +)
- Lasts for decades outdoors
- Can be easily repaired or custom-made
Why Coax Still Fails on Multiband Antennas
Coax works best when it sees 50 Ω — and only if it’s short, dry, and shielded properly. On multiband antennas where impedance swings wildly (100 Ω → > 1000 Ω), coax becomes a lossy transmission line. Even premium coax suffers from dielectric and skin-effect losses at high SWR.
Final Thoughts
If you’re serious about efficient HF operation across multiple bands — especially with high power — then 600-ohm open-wire line remains the gold standard. It outlasts, outperforms, and outmatches TV twin-lead and coax in nearly every technical aspect.
Yes, it’s a bit more work to install, and you’ll need a decent tuner and a good 1:1 current balun — but the performance rewards are exceptional.
A good feedline is not just a wire — it’s part of your antenna system. For multiband HF, open-wire is simply unbeatable.
Mini-FAQ
- Can I use 450 Ω window line instead? — Yes, but it has higher dielectric loss and detunes in wet weather; 600 Ω open-wire remains superior.
- Do I need a choke balun? — Only if you transition to coax in the shack. Keep the open-wire balanced and symmetrical to prevent common-mode current.
- Is 600 Ω line affected by rain or snow? — Hardly. Air dielectric and wide spacing make it nearly immune to moisture-related detuning.
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