Most hams think "feedline" means coax. It's the default, the familiar, and what the radio comes with. But coax is just ONE type of transmission line, and it's not always the best choice. Balanced feedlines — ladder line, open wire, and twin-lead — have been connecting radios to antennas since before coax was invented, and they still offer advantages that coax can't match.

Understanding all your feedline options lets you choose the RIGHT one for each situation instead of defaulting to coax out of habit.

Types of Transmission Lines

Coaxial Cable (Unbalanced)

Structure: Center conductor surrounded by dielectric insulator, surrounded by shield, surrounded by jacket.

Impedance: 50Ω (standard ham) or 75Ω (CATV).

Key property: Shield contains all fields — no radiation from the feedline. Can be routed anywhere (along metal, through walls, buried) without affecting performance.

Disadvantage: Loss increases with SWR. High SWR = dramatically higher loss.

Ladder Line (Window Line)

Structure: Two parallel conductors separated by periodic plastic spacers ("windows" cut in the plastic web between wires).

Impedance: 300-450Ω depending on wire spacing and diameter.

Key property: Extremely low loss — even at high SWR, loss remains low. A 100-foot run of ladder line with 10:1 SWR loses less power than 50 feet of coax with 3:1 SWR.

Disadvantage: Must be kept away from metal (6+ inches), can't be easily routed through walls, affected by proximity to conductors.

Open Wire Line

Structure: Two bare conductors separated by periodic ceramic or plastic spacers.

Impedance: 400-600Ω (depends on spacing and wire diameter).

Key property: Lowest loss of any practical feedline type. Used in broadcast transmitter installations and multi-band wire antenna systems.

Disadvantage: Delicate, requires standoff insulators for routing, can't touch anything conductive.

Twin-Lead (300Ω TV Lead)

Structure: Two conductors molded into flat plastic ribbon.

Impedance: 300Ω.

Key property: Cheap, available (TV antenna lead-in), adequate for receive and low-power applications.

Disadvantage: Dielectric absorbs water (loss increases dramatically when wet), limited power handling, UV-degrades outdoors.

When to Use What

Use Coax When:

  • Antenna is resonant (SWR < 2:1 on the operating frequency)
  • Feedline must route along metal, through walls, or underground
  • Convenience matters (no routing restrictions)
  • You want plug-and-play (most radios have coax connectors)
  • Single-band antenna matched to 50Ω

Use Ladder Line When:

  • Antenna is NOT resonant on all desired bands (multi-band wire with tuner)
  • You need very low loss across wide SWR range
  • You can route the feedline away from metal (6+ inch clearance)
  • You're using a balanced antenna tuner (or balun at the tuner)
  • You want the best efficiency for a multi-band wire antenna

The Classic Use Case: Doublet + Ladder Line + Tuner

A 130-foot wire (doublet) fed with ladder line to a balanced tuner:

  • Works ALL bands from 80m through 10m
  • SWR varies wildly per band (10:1 or higher on some)
  • Ladder line handles the high SWR with minimal loss
  • Tuner matches whatever impedance arrives at the shack
  • Total system efficiency: 85-95% on all bands

The same antenna fed with coax:

  • High SWR on non-resonant bands
  • Coax loss at high SWR: 3-6 dB or MORE (50-75% power lost in the coax!)
  • Tuner can match it, but the power is already wasted in the coax
  • Total efficiency: 25-60% on non-resonant bands

The difference is enormous. This is WHY ladder line exists.

The Physics: Loss vs SWR

Why Coax Fails at High SWR

Coax loss is specified at SWR 1:1. When SWR increases, loss increases because:

  • Current at high-SWR points is much higher than average (I²R losses increase)
  • Voltage at high-SWR points is much higher (dielectric heating increases)
  • The loss multiplier compounds with each SWR cycle along the cable

Example (100 ft RG-213 on 7 MHz):

  • SWR 1:1: 0.6 dB loss (13%)
  • SWR 3:1: 1.0 dB loss (21%)
  • SWR 5:1: 1.5 dB loss (29%)
  • SWR 10:1: 2.5 dB loss (44%)
  • SWR 20:1: 3.8 dB loss (58%)

Why Ladder Line Doesn't Care

Ladder line's matched loss is extremely low (~0.1 dB/100 feet at HF). Even multiplied by high SWR, the total remains small:

  • SWR 1:1: 0.1 dB loss (2%)
  • SWR 10:1: 0.5 dB loss (11%)
  • SWR 20:1: 0.8 dB loss (17%)

Even at 20:1 SWR, ladder line loses less than coax at 2:1 SWR. This is the fundamental advantage.

Impedance Transformation

Transmission Lines Transform Impedance

A key concept: transmission lines CHANGE the impedance as seen at their input end depending on:

  • The load impedance (antenna)
  • The line's characteristic impedance
  • The line's ELECTRICAL length (in wavelengths)

Special cases:

  • Half-wave line (λ/2): impedance at input = impedance at load (no transformation)
  • Quarter-wave line (λ/4): impedance inverts. Z_in = Z_line² ÷ Z_load

Practical implication: A 50Ω antenna connected to 100 feet of 50Ω coax won't appear as 50Ω at the radio end if there's any mismatch. The impedance rotates around the Smith chart as line length changes. The tuner at the radio end must handle whatever impedance arrives.

With a Tuner

When using an antenna tuner:

  • The tuner matches whatever impedance appears at its terminals to 50Ω for the radio
  • The feedline between tuner and antenna carries whatever SWR the antenna presents
  • Feedline loss at that SWR determines how much power reaches the antenna
  • LOW-LOSS feedline (ladder line) = more power to antenna when SWR is high

Practical Installation: Ladder Line

Routing Rules

  • Keep 6+ inches from any metal (gutters, siding, conduit, towers)
  • Keep perpendicular to any parallel metal run
  • Can cross metal at right angles briefly
  • Route away from building exterior metal surfaces
  • Use standoff insulators (4-6 inch standoffs screwed to building)

Building Entry

Option 1: Through window/wall with standoff

  • Drill two holes (one per conductor) through wall
  • Insert PVC tube insulation in holes
  • Feed conductors through (no metal contact)
  • Seal around tubes weatherproof

Option 2: Convert to coax at building entry

  • Balun at entry point (4:1 converts 300-450Ω to ~75-100Ω)
  • Short run of coax from balun to tuner inside
  • Minimizes coax length (and SWR-related loss) to a few feet

Option 3: Bring ladder line all the way to tuner

  • Best efficiency (no transition)
  • Requires routing ladder line through the shack to the tuner
  • Less convenient but lowest loss

Weatherproofing

  • Ladder line itself is weatherproof (plastic spacers, stranded wire)
  • Water on the line slightly affects impedance/loss (usually negligible)
  • Twin-lead (300Ω ribbon): absorbs water badly. Use WINDOW line or open wire for outdoor runs.
  • Ice loading: add strain relief support (ladder line is light but ice is heavy)

Building Your Own Ladder Line

DIY Open Wire Line

Materials:

  • Two runs of 14 AWG stranded insulated wire
  • Spacers every 6-12 inches (cut pieces of PVC pipe, or drilled plastic strips)
  • Cable ties or wire through spacer holes

Spacing: 2-4 inches between conductors Impedance: ~400-500Ω (depends on spacing and wire diameter)

Construction:

  1. Cut both wires to length (same length!)
  2. Every 12 inches: insert a spacer between wires, secure with cable tie through spacer
  3. Keep spacing consistent
  4. Result: homebrew ladder line at minimal cost

Commercial Ladder Line

  • Wireman 551 (450Ω window line): $0.40-0.60/foot. The standard.
  • Wireman 553 (300Ω): heavier, lower impedance
  • DX Engineering: various options with strong spacers

The Multi-Band Wire Station

The Best HF Antenna System for Most Hams

  1. Antenna: 130-135 foot wire (center-fed doublet)
  2. Feedline: 450Ω ladder line from antenna feedpoint to shack
  3. Tuner: Balanced antenna tuner (Johnson Matchbox, Palstar BT1500, or internal tuner + 4:1 balun)
  4. Result: Efficient all-band operation from 80m through 10m with ONE antenna

Why this works:

  • Wire is resonant (or near-resonant) on multiple bands
  • Non-resonant bands: high SWR, but ladder line handles it efficiently
  • Tuner matches all bands to 50Ω for the radio
  • Total system loss: 0.5-1.5 dB on any band (vs 3-6 dB with coax at high SWR)

This setup outperforms compromise multi-band antennas (trap verticals, OCF dipoles) in efficiency while using nothing more than wire, spacers, and a tuner. It's the antenna system that antenna experts actually use at home — because it WORKS on every band with minimal compromise.

When Coax Wins

Despite ladder line's advantages, coax is still the right choice when:

  • Your antenna is resonant on your operating bands (SWR < 2:1)
  • You need to route through walls, along metal, or underground
  • You're connecting to a beam antenna on a tower (coax at the rotator)
  • Convenience and simplicity outweigh the efficiency margin
  • You're using a monoband antenna that's already matched to 50Ω

For resonant antennas with good SWR, coax loss is minimal and the routing convenience wins. For multi-band wire antennas with varying SWR, ladder line wins by a wide margin.