The Phantom Third Conductor

Open-wire (ladder) line has a deserved reputation ... low loss, happy at high SWR, and wonderfully honest about impedance transformation. But there’s a catch that only shows up when the system isn’t truly balanced.

The moment you drive a balanced line out of balance, you unintentionally create something that doesn’t exist on the schematic: a third “conductor” made out of your surroundings ... tuner cabinet, coax shield, station ground, house wiring, gutters, mast, and sometimes even you.

That “phantom conductor” is where unwanted return currents go. The effect is absolutely analogous to coax carrying current on the outside of the shield ... it’s just expressed differently because open-wire has no shield.

What open-wire does brilliantly ... when it stays balanced

A true two-wire line supports a differential mode:

• Current goes out on one conductor.
• An equal-and-opposite current returns on the other conductor.

When those currents are equal and opposite, the external fields largely cancel. The line tends to radiate less, pick up less, and behave like a predictable transmission line.

Here’s the key point that gets missed: balance isn’t just “the wires look symmetric.” Balance means each conductor has the same impedance to its surroundings (the local reference ... usually earth and nearby objects). If those impedances aren’t equal, the system is not balanced even if the conductors are physically identical.

When you “feed it crooked” ... the in-phase component appears

If the two conductor currents aren’t equal and opposite, you can think of what’s happening as two components riding on the pair:

• Differential current (wanted) ... equal magnitude, opposite direction.
• In-phase current (unwanted) ... the same direction on both conductors.

Once that in-phase component exists, it needs a return path ... and that’s where the “phantom third conductor” shows up. Open-wire can’t magically force that return to stay on “the other wire” anymore, because the system has stopped behaving like a clean two-conductor world.

What causes the imbalance in real installations

• One side of the antenna is closer to a building, tree, ground, or roof edge than the other.
• The line runs closer to metal on one side (mast, gutter, flashing, tower leg, siding).
• A tuner/output network is unbalanced (many are) while feeding a balanced line.
• The transition to coax or station equipment “references” one side more strongly to the chassis/ground environment.
• The last meters near a house entry become asymmetrical (window frame, conduit, wiring bundles).

So where do the unwanted return currents go?

The uncomfortable answer ... everywhere they can.

In a perfectly balanced pair, return current is neatly confined: it returns on the other conductor. But when the system is driven out of balance, the stray return current returns through capacitance and coupling to the environment:

• tuner case / enclosure
• shack “ground” wiring and bonding
• coax shield (if coax exists anywhere downstream)
• AC safety ground wiring
• computer/audio/interface cables
• your body (yes, really)

That’s why imbalance correlates so strongly with classic symptoms:

• RF in audio, hot mic cases, keyboard/mouse glitches
• RFI to nearby electronics
• “my tuning changes when I touch the tuner”
• pattern distortion and unexpected lobes because the feedline/station became part of the radiator

Is this “the same thing” as coax shield current?

Yes ... the physics is the same (multiple modes can exist), but the mechanics look different.

Coax

In its intended TEM mode, coax carries equal-and-opposite currents on the center conductor and the inside surface of the shield. Ideally, the outside of the shield carries no RF. When the system is excited out of balance, however, the outside of the shield can carry current and become a radiator and noise pickup structure.

Open-wire

Open-wire has no shield, so there is no neat “outer braid” conductor to point at. Instead, the in-phase component rides on both wires together, and the return path becomes the surrounding world. In both cases, the result is the same:

• Feedline behavior turns into “feedline plus station environment” behavior.
• Unwanted currents appear in places you never intended ... because the system created a third path.

Why the “right” balun often belongs near the shack

The most common place where balanced systems go to die is the transition zone ... where the clean two-wire world meets the messy station world. Outdoors, the open-wire may be beautifully symmetric in free air. Then near the house:

• it runs near brick, flashing, gutters, metal frames
• it enters a building (asymmetric environment)
• it connects to an unbalanced tuner or station reference
• it transitions to coax (explicitly unbalanced line)

This is exactly where a current balun / line isolator earns its keep ... it presents a high impedance to the in-phase component, forcing current to return on the other conductor instead of recruiting your station as the missing return path.

What the balun is doing ... in plain language

A current balun is trying to enforce this rule: whatever current goes out on one wire must come back on the other wire ... not on the tuner case, not on the coax shield, not on the shack wiring.

Placing that choke/balun at the open-wire end (shack entry, outdoor tuner box, or open-wire-to-coax transition) often gives the biggest practical win: it keeps stray return currents from entering the station.

Why not at the feedpoint?

Choking at the feedpoint can be excellent for pattern integrity and for keeping the entire feedline from becoming “part of the antenna.” But with open-wire systems, feedpoint placement can be mechanically and electrically painful:

• impedances can be extreme and highly variable across bands
• weatherproofing and strain relief are harder
• the main real-world pain point is often “RF in the shack,” best solved at the shack end

So this approach is a common, practical compromise: keep the line as clean as possible outdoors ... then block the unwanted current component right before it can ride into the station environment.

Why any coax before an indoor tuner should be short

If the tuner is in the shack, then any feedline between the antenna system and that tuner may be operating at high SWR. Open-wire can usually tolerate that with very low loss. Coax often cannot ... because mismatch loss can rise sharply under severe SWR, and voltages/currents along the coax can get ugly.

So if your chain is:

open-wire → current balun → coax → tuner (in shack)

... that coax segment is living on the wild side (high mismatch). Keep it short, and make sure it can’t become the convenient return path for stray currents.

Even better when possible: put the tuner outdoors at the transition point, so coax is on the matched 50 Ω side ... then coax length becomes far less critical and far less “exciting.”

TX vs RX ... why the symptoms differ

On transmit

On TX, stray return currents are loud, literal, and sometimes painful:

• they drive RF onto the station environment and cables
• they increase RFI risk and “RF in the shack” symptoms
• they can distort the intended radiation pattern by making the feed system part of the radiator

On receive

On RX, the currents are tiny, so you don’t get burns ... but the same mechanism still matters because of noise pickup. A well-balanced two-wire line tends to reject noise that couples equally to both conductors. But if the last meters near the house become asymmetric, the line can start “listening” to local wiring noise through that same phantom return path.

Practical RX verdict:

• Balanced open-wire done right ... often quieter.
• Open-wire allowed to go unbalanced near the house ... can get noisy.
• Coax with outside shield current ... frequently becomes an excellent pickup antenna for household noise.

A practical checklist that matches this philosophy

If your goal is “keep the open-wire balanced outdoors, and prevent it from dragging the shack into the antenna,” this pattern is proven:

• Dress the open-wire symmetrically ... keep equal spacing from metal and surfaces as much as practical.
• Respect the last meters ... treat the shack entry as the danger zone for imbalance.
• Install a current balun / line isolator at the boundary ... outdoor tuner box, entry panel, or open-wire-to-coax transition.
• If coax exists before an indoor tuner, keep it short ... because it may be operating at high mismatch.
• Reduce “easy” return paths ... tidy bonding, avoid random parallel cable runs, keep the transition physically compact and deliberate.

Closing thought

Open-wire doesn’t magically eliminate unwanted currents ... it makes them obvious. The moment the system becomes asymmetric, the station environment can become the missing return path: the phantom third conductor.

Put a current balun/choke at the end of the open-wire line (or at the transition to coax), keep any pre-tuner coax short, and you keep those stray return currents outdoors ... where they belong.

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