Why an Inverted-V with Ladder Line Is More Stable Than Coax + Balun
Why an Inverted-V with Ladder Line Is More SWR-Stable Than Coax + Balun (Especially on 160 m)
An inverted-V is a fantastic low-band workhorse. But how you feed it determines how much of your rig’s power actually makes it to the antenna. On 160 m, where antennas are electrically low and impedances swing widely, a ladder-line feed often remains far more SWR-stable at the shack than a coax-plus-balun feed.
The 160 m Problem: Big Wavelengths, Touchy Impedances
A half-wave on 160 m is ~80 m. Most inverted-V installations are relatively low (in wavelengths), so feedpoint impedance moves around with height, angle, soil, and even weather. With coax, any high SWR turns into real, cumulative loss—and a balun can be driven into poor behavior at the extremes. The result: more heating and less radiated power.
Why Ladder Line Stabilizes SWR
Ladder line (open-wire) is both low-loss and an impedance transformer. Its electrical length (βℓ) rotates the load on the Smith chart, frequently moving “awkward” impedances into a tuner-friendly window. Because losses are tiny, it doesn’t “burn off” mismatch like coax would—so more power survives to the antenna.
Suppose you measure at the shack about 2:1 SWR at 1.8 MHz and 4:1 at 2.0 MHz with an inverted-V on ~16 m of 600 Ω ladder line (VF≈0.98). By shortening or lengthening the ladder line a few meters, you change its electrical length just enough to re-map the antenna’s impedance so the tuner sees a smoother, lower-stress range—often into roughly ~1.3:1 → 3:1 across the band edges.
The key: you’re not “fixing” the antenna with the line—you’re using the line’s low-loss impedance shift to place the tuner in its comfort zone.
Why not coax? With coax, the same mismatch is carried as real loss. A 20 Ω load on a 50 Ω coax line shows a 2.5:1 SWR; at 160 m, even “low-loss” coax can add multiple dB of attenuation. Stretch the mismatch to 4:1 and the loss compounds quickly. Instead of transforming the impedance into something easier for the tuner, coax just dissipates more power as heat. Worse, the balun at the feedpoint is now forced to operate into extreme impedances and reactive loads, where saturation and extra heating further degrade performance.
In short: ladder line transforms, coax punishes. On 160 m, where line lengths are long and impedances swing wildly, this difference decides whether your system radiates strongly or just warms up the coax jacket.
Representative values for ~16 m of feedline, 20 Ω antenna load, ~1.5 kW PEP. Loss figures rounded. Actual numbers vary with soil, height, and installation.
| Feedline | Matched loss (1:1) | Effective SWR loss (2.5:1) | Power lost | Notes |
|---|---|---|---|---|
| 600 Ω ladder line (~16 m) | ~0.05 dB | ~0.1 dB | <3 % | Loss negligible; impedance shift helps tuner. |
| RG-213 coax (~16 m) | ~0.2 dB | ~1.0–1.5 dB | 20–30 % | Mismatch loss dominates; balun stressed. |
Takeaway: On 160 m, coax converts mismatch directly into heat; ladder line carries it with almost no penalty while transforming impedance into safer ranges.
Practical Tuning Recipe (Fast)
- Start with what you have (e.g., 16 m of ladder line). Measure SWR at 1.8 and 2.0 MHz at the shack.
- Add or remove ~2–3 m, re-measure both edges. Then iterate in ~1 m steps to favor your preferred part of the band.
- Place a 1:1 current choke at the tuner’s balanced output (or use a true balanced tuner) so common-mode doesn’t fake your readings.
- Avoid ladder-line lengths approaching odd quarter-wave multiples at mid-band (worst inversions). On 160 m that’s ~40 m electrical—well above these lengths.
- Don’t chase absolute minimum SWR; ladder line is low-loss. A shack-end 2–3:1 that your tuner handles easily is usually a net win.
- Higher apex = smoother impedance. If you can get the center higher on 160 m, the whole system behaves better.
Coax + Balun vs. Ladder Line — Summary
- Coax + Balun: convenient but mismatch loss rises quickly on 160 m; balun behavior can degrade at extreme R±jX.
- Ladder line: negligible loss under mismatch and deliberate impedance shift to keep the tuner in its sweet spot.
Mini-FAQ
- Do I still need a tuner? — Yes. Ladder line doesn’t “fix” the antenna; it positions the impedance so your tuner works lightly.
- Why is coax a problem on 160 m? — High SWR turns into real loss with coax at these lengths/frequencies; ladder line doesn’t penalize you the same way.
- How much should I trim? — Start with ±2–3 m, then fine-tune in 1 m steps while watching both band edges.
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