Ladder Line vs Coax: Feedline Loss, SWR and Which to Choose

Every antenna needs a feedline, and the choice often looks like a matter of taste. Many amateurs buy coax because it is convenient and then wonder why a multiband wire loses so much signal when the SWR is high. Others hear that ladder line vs coax is a contest that ladder line always wins, and then struggle with tuners, wet weather and cables that refuse to enter the shack. Neither view is complete. This guide explains how the two cable families differ, what actually causes loss, why a feedline with high SWR can be a good solution, and how to decide which one belongs in your own installation.

Two Different Kinds of Transmission Line

Coaxial cable has a centre conductor surrounded by a dielectric and a braided or solid shield. The shield confines the field inside the cable, which is why you can run coax along a wall, bury it in conduit or bundle it with other cables. It is an unbalanced line, with the signal on the centre conductor and the return current on the inside of the shield.

Ladder line is a balanced line, a pair of parallel conductors held apart by insulating spacers or a plastic web. The family includes twin lead, window line and open wire line. Typical characteristic impedances run from about 300 ohms for ribbon twin lead and 300 to 450 ohms for window line to the range of roughly 500 to 650 ohms for open wire ladder line. The two wires carry equal and opposite currents, so their fields cancel at a distance, as long as the line is kept symmetrical and away from metal.

That last point is the root of most of the practical differences. Coax hides the signal inside a shield, so its behaviour barely depends on what is nearby. Ladder line exposes its field to the world. When it is well balanced and kept clear of clutter, it is wonderfully efficient. When a gutter, a drainpipe or a metal mast comes close, the balance is disturbed and the impedance and the loss change.

Where Feedline Loss Comes From

Two separate effects add up in a practical station, and both matter in the ladder line vs coax decision.

• Matched loss. This is the loss of the cable when it is terminated in its own characteristic impedance. It comes from the resistance of the conductors and from losses in the dielectric. It rises with frequency and with the length of the run. Thin, small-diameter coax has a high matched loss on the upper bands.
• Additional loss due to SWR. When the load does not match the line, part of the power is reflected and travels back and forth on the cable. Each trip adds more conductor and dielectric loss, so the actual loss is higher than the matched loss. The higher the SWR and the lossier the cable, the larger the extra penalty.

The comparison is dramatic at HF. As one reference puts it, a common thin coax such as RG-58 loses about 6.6 dB per 100 metres at 30 MHz, while 300 ohm twin lead loses only about 0.55 dB for the same length and frequency. The exact figures vary with the specific cable and with age and moisture, but the order of magnitude is typical. Balanced line has very low matched loss because there is no solid dielectric to absorb energy and the conductors can be relatively thick and widely spaced.

That difference becomes decisive when the SWR is high. A multiband dipole or doublet cut for a single band, used on others, can present a feedpoint impedance far from 50 ohms. A piece of low-loss ladder line with a high SWR can still lose very little, while a length of thin coax in the same situation would waste a large part of the power. This is the basic reason that the classic multiband antennas, such as the doublet with ladder line described in our guide to the doublet antenna with ladder line, are fed with balanced line.

It helps to remember what SWR is and what it is not. The standing wave ratio describes how much of the power is reflected at the load, and it says nothing by itself about how much is lost on the way. A reading of 6:1 on a short run of low-loss open wire may cost a fraction of a decibel, while the same reading at the end of a long run of thin coax can cost several decibels. The meter at the transmitter looks the same in both cases, which is why the choice of cable matters more than the number on the display. The transmitter also has to be able to live with the mismatch it sees, so a tuner is part of the system, not an optional extra.

Think of the feedline as part of the antenna system. The antenna radiates, the line carries power to it, and the tuner makes the transmitter comfortable. If one part is poor, the whole system underperforms, and the cheapest improvement is often a better cable or a better route for the one you have.

What Coax Does Better

With all that talk of loss, it is easy to overlook why coax is still the default.

• Simple installation. Coax can be attached to walls, taped to a mast and run near metal, and it can be buried or put into conduit.
• Easy entry to the shack. A wall feedthrough or a connector panel handles it with no special measures.
• Low noise pickup. A good shield rejects interference from household wiring, which is especially valuable for receiving in a noisy environment.
• Standard connectors and a 50 ohm match. Every transceiver, amplifier, switch and meter expects 50 ohm coax. Resonant antennas such as a dipole at a good height, a quarter-wave vertical or a beam are designed for it.
• Predictable behaviour. The impedance does not change when the weather does or when the cable passes near another object.

If an antenna presents a modest SWR on the band you use, quality coax works well. Our comparison of RG-58, RG-8X and LMR-400 shows how the different grades behave at HF and VHF. For a resonant antenna on a single band, a short run of low-loss coax will lose very little, and the convenience is hard to beat.

What Ladder Line Does Better

• Very low loss, even with a mismatch. This is what makes it the right feedline for multiband wire antennas that are not resonant on every band.
• High power handling. Without a lossy dielectric, there is little heating, and the limit is usually voltage, which depends on the spacing.
• Low cost per metre for open wire. A homemade open wire line can be built from wire and spreaders. Window line is inexpensive and lightweight.
• Freedom from a fixed impedance. You are not trying to force the antenna to look like 50 ohms. The tuner does that job at the shack end.

The cost is that you must tolerate its habits. The line needs a tuner that is happy with high or reactive loads, and the tuner needs a balanced output, or a balun on the output, to connect balanced line to an unbalanced transmitter. Our guide to baluns and ununs describes the options, and the article on choosing an external antenna tuner explains what to look for in a tuner that can handle the extremes.

Comparison Table

Routing Rules for Balanced Line

Ladder line behaves best when you respect a short list of habits.

• Keep it away from metal. Gutters, downspouts, wires and metal masts distort the balance. A common guideline is to keep it clear by several times the spacing between the conductors, and the more clearance the better.
• Avoid sharp bends. Turn corners gradually. Sharp kinks can change the impedance locally and add loss.
• Keep the two wires symmetrical. The line should leave the antenna at the same distance from both sides. Standoffs made from non-metallic materials help keep it away from the building.
• Twist if you must. A modest number of twists in window line can help it run alongside a structure without disturbing the balance, but do not exceed what the manufacturer recommends.
• Use a proper entry. Bring it through a window or a wall with an insulated feedthrough, then connect it to the tuner with short, tidy runs. Take care not to leave the high voltage points exposed where a person or a pet could touch them.
• Watch the weather. Wet snow, ice and heavy rain can change the characteristics of window line. Open wire is less sensitive, but it is bulkier.

Common Mode Currents

Balanced line only stays balanced if the antenna and the shack stay balanced. If current flows on the outside of the line or in the transmitter case, you get common mode radiation, noise pickup and unpredictable SWR readings. Several things help. Use a good current balun or choke at the point where balanced line meets coax. Keep the line from running parallel to long wires. Try to keep the antenna symmetrical. And remember that the length of the line can affect the common mode current, which is why moving or lengthening the feedline sometimes changes how a station behaves.

The same reasoning applies to coax-fed antennas. Our article on what an SWR meter tells you and what it hides explains why a simple SWR reading at the transmitter can mislead when there is loss or common mode current.

Choosing for Your Station

A short decision guide helps.

• Single-band resonant antenna, beam or vertical. Use coax of a suitable quality. The SWR will be low and the cable is easy to install.
• Multiband wire fed at the centre, such as a doublet or a G5RV type. Use ladder line or window line to the shack, with a balanced or balun-equipped tuner. This arrangement keeps the loss low on every band.
• Long runs on the upper bands. Choose low-loss coax or consider balanced line if the antenna is not resonant. A long run of thin coax at a mismatch is the worst combination.
• Noisy location with a receive priority. Coax with good common mode attenuation is likely to be quieter.
• Portable and field use. A short piece of coax is usually more practical. A roll of window line can be useful for a quick doublet, but it needs careful handling.
• Remote tuner at the antenna. Put the tuner at the feedpoint and use coax from there to the shack. The tuner then matches the antenna, and the coax runs at a low SWR.

Use a cable analyzer to check the actual feedpoint impedance before deciding. The measurement shows whether the SWR on the band is moderate or extreme, and many free calculators can estimate the total loss of a given cable at that SWR and frequency.

The Bottom Line

The ladder line vs coax debate has no universal winner. Coax is the convenient, quiet and predictable choice for resonant antennas and anywhere you need to run a cable near metal. Balanced line is the efficient, economical choice for multiband wires, especially when the SWR is high, but it demands good routing, a balun and a tuner that can cope. Pick the feedline that fits the antenna you actually have, measure rather than guess, and do not let a single number such as SWR decide for you. A station that uses both, with coax for the beam and verticals and ladder line for the wire, is often the most practical solution.

Frequently Asked Questions

Is ladder line really lower loss than coax?

Yes. A published comparison gives about 6.6 dB per 100 metres for RG-58 coax at 30 MHz against about 0.55 dB for 300 ohm twin lead. The gap widens when the SWR is high.

Can I connect ladder line directly to my transceiver?

No. A transceiver expects an unbalanced 50 ohm load. Use a tuner with a balanced output, or a balun and tuner, to connect balanced line to the radio.

Why does ladder line work well with a high SWR?

Its matched loss is so low that even with repeated reflections the extra loss remains small. Coax, especially thin coax, adds far more loss in the same situation.

How close can ladder line be to a metal object?

As far as practical. Metal near the line disturbs its balance. Keep it clear by several times the conductor spacing and use non-metallic standoffs.

Is window line better than open wire?

Window line is lighter and easier to handle, but wet weather affects it more. Open wire has the lowest loss and handles weather well, but it is bulkier and needs spacers.

Which is better for a quarter-wave vertical?

Coax. The vertical is designed to present about 50 ohms, so coax gives a low SWR, easy routing and low noise pickup.