Routing Coax for HF Antennas (1–30 MHz)

If you listen to enough HF antenna advice, you’ll hear all of these statements, often from good operators:

• “Just bury the coax and you’ll stop RF in the shack.”
• “Never bury coax... your SWR will go crazy.”
• “Your dipole feedline must drop straight down at exactly 90°.”
• “EFHWs need a certain coax length to tune right.”
• “OCFs are magic; no choke needed.”

The confusion comes from mixing two very different topics: mechanical routing, which protects the cable, avoids water ingress, avoids UV, and prevents tripping hazards; and RF current control, which stops unwanted current on the outside of the coax shield.

Once you separate those, the “rules” stop sounding contradictory.

The One Concept That Explains Most Coax-Routing Problems

Routing and burying decisions matter most when common-mode / stray return RF current exists. If you stop it with proper feedpoint design and intentional choking, coax routing becomes mostly a mechanical and weatherproofing issue.

Universal Coax Routing Rules for HF

Don’t Let the Coax “Hug” the Radiator

For the first part of the run leaving the feedpoint, avoid running the coax parallel and close to the antenna wire, mast-mounted vertical element, or one leg of a dipole.

Better: leave the antenna area quickly, at a right angle if practical, then route wherever you want.

Why it matters: if there is any common-mode / stray return RF current, a parallel run couples strongly and encourages the coax shield and nearby objects to participate in radiation.

Cross Other Conductors at 90° When You Can

If your coax must cross antenna wires, radials, fence wires, house wiring, or metal gutters/downspouts, crossing at a right angle reduces coupling.

Use Strain Relief and Drip Loops Outdoors

• Strain relief at the feedpoint: do not let the connector carry the cable weight.
• Drip loop before any enclosure or building entry: water follows the cable.

Weatherproof Every Outdoor Connector Properly

Outdoor coax failures are usually water ingress, not mysterious RF behavior.

• Keep connections out of puddle zones and off the ground.
• Seal with self-amalgamating butyl rubber tape as the inner layer plus a UV-resistant overwrap as the outer layer.
• Avoid burying connectors or splices. Bring splices into an above-ground junction box.

Add Choking Intentionally

If you do nothing else, use a proper common-mode choke or current balun where it matters for your antenna type, and consider a second choke at the shack entry if you fight RF in the shack or noise pickup.

“Choking” means forcing the feedline to behave like a feedline instead of becoming part of the antenna via common-mode / stray return RF current.

Burying Coax Is Mainly a Mechanical Decision... Unless Your Coax Is Radiating

Bury coax because you want protection, a tidy install, and fewer mechanical failures. Do not expect burying alone to fix RF.

If common-mode / stray return RF current is present, burying can change SWR and performance with soil moisture because you unintentionally buried part of the antenna or return system.

When to Bury Coax, and When Not To

Bury Coax When

• It is a permanent or semi-permanent installation.
• You want protection from damage and UV.
• You want predictable routing and fewer mechanical failures.
• You have already managed common-mode / stray return RF current, or your design inherently keeps it low.

Don’t Bury Coax, or Don’t Bury It Yet, When

• You are still experimenting with antenna placement and feedpoint setup.
• You have an EFHW or other unbalanced feed where the coax may be acting as a return path and you have not controlled that yet.
• You would end up burying a splice or connector.

Practical Burying Tips

• Use direct-burial rated coax if it is actually going in soil. Otherwise run standard coax inside conduit.
• Avoid tight bends; follow the coax minimum bend radius.
• Route with gentle curves, not kinks.
• Never bury PL-259/SO-239 splices as-is. If you must splice, bring it up into a weatherproof junction box above ground.
• Call your local utility locate service before digging and follow local practices/codes for depth.

Dipoles: Coax Routing That Actually Matters

A center-fed dipole is balanced in principle. Coax is not the problem by itself, but direct coax feed without effective current choking can allow common-mode / stray return RF current on the outside of the shield and produce pattern skew.

Best-Practice Setup

• Use a 1:1 current balun or an effective choke at the feedpoint.
• Route the coax away so it does not run alongside either leg.

Does the Coax Have to Drop Straight Down?

Not perfectly. The real goals are: do not run parallel to one leg for a long distance, get some distance before turning, and use a current balun/choke so routing becomes less critical.

Rule of thumb: leave the feedpoint at roughly a right angle for a few meters, then route as needed.

When Burying Is Fine for Dipoles

With a proper feedpoint choke or balun, burying is usually purely mechanical. A buried coax run feeding a well-choked dipole is common and stable.

OCF Dipoles: Why Coax Routing Gets People in Trouble

OCF dipoles are popular because they can be multiband and easy to deploy, but they are more likely to create common-mode / stray return RF current on the feedline than a center-fed dipole.

Why OCFs Create More Feedline Issues

• The feedpoint is not symmetrical.
• Each side couples differently to ground, nearby structures, and the feedline.
• Even with a transformer, some common-mode / stray return RF current may remain unless a strong current choke is used.

Best-Practice Setup

• Use the recommended transformer for the design, commonly 4:1 depending on the specific OCF design.
• Add a strong common-mode choke at or very near the feedpoint.
• Consider a second choke near the shack entrance if you have RFI or receive noise pickup.

Routing Advice That Helps OCFs Most

• Avoid routing the coax close and parallel to the longer leg.
• Leave the feedpoint area cleanly; get distance before you turn.
• If the OCF is near the house, avoid running alongside gutters, siding, or wiring unless common-mode / stray return RF current is well-controlled.

The “Coax Length Matters” Myth

With OCFs, changing coax length can change how common-mode / stray return RF current behaves, so SWR may shift when you add or remove coax. That leads to folklore about “the right coax length.”

Better approach: treat “coax length makes it tune” as a sign you need more choking or better feedpoint balance. If you want the deeper why, see: Why minimum coax length matters for HF antennas.

EFHW: Where Most Coax Routing Confusion Comes From

EFHW antennas are intentionally end-fed. They can work extremely well on HF, but their feed system still needs a return path. If you do not provide one, the feedline shield and nearby structures often become it via common-mode / stray return RF current.

The EFHW Reality: the Coax May Be Part of the Antenna

If common-mode / stray return RF current is present, routing changes the antenna system. Burying can shift SWR with soil moisture and season, coax length changes can affect tuning, and RF in the shack becomes more likely.

Three Common EFHW Strategies

Strategy A: Provide a Defined Return, Then Choke Hard

• Add a dedicated counterpoise or radial system at the transformer/feedpoint reference side.
• Use a common-mode choke right at or very near the transformer output to keep common-mode / stray return RF current off the long coax run.
• Optional second choke at the shack entrance.

This is the approach that makes coax routing the least mysterious.

Strategy B: Let Some Feedline Participate... But Stop It Before the Shack

• Route coax away from the radiator cleanly.
• Place a choke some distance down the line, not right at the feedpoint.
• Add another choke at the shack if needed.

This can work well, but it is more sensitive to routing and environment because the first coax section is intentionally part of the RF structure.

Strategy C: No Defined Return, Minimal Choking

It may still make contacts, but it is the least predictable and most likely to produce “SWR changes when it rains,” “magic coax length,” and RF in the shack.

EFHW Routing Rules That Reduce Problems

• For the first several meters, keep coax away from and not parallel to the EFHW wire.
• Avoid routing along metal structures that can re-radiate RF unless common-mode / stray return RF current is well-controlled.
• If you plan to bury the coax, do it after you have decided your return/choking strategy.

Verticals: When Burying Coax Is Normal, and When It Is Not Enough

Ground-Mounted Quarter-Wave Vertical with Radials

In a classic ground-mounted vertical, the radial field is the return path. With a decent radial system, the feedline is less likely to become part of the antenna.

• A choke at the base can still help reduce common-mode / stray return RF current and keep RF out of the shack.
• Routing coax along the ground or burying it is usually fine and stable.

Elevated Verticals or “No Radials” Verticals

When the vertical is elevated, or when the “ground” system is minimal, the coax shield often tries to become the return path.

• Provide elevated radials or counterpoise wires at the feedpoint.
• Use a common-mode choke at the feedpoint to keep common-mode / stray return RF current off the coax.
• Route coax down and away cleanly; burying is fine after choking.

Vertical Dipoles / Coax-Fed Vertical Dipoles

Vertical dipoles are balanced radiators and generally behave more like dipoles: use a current balun or choke at the feedpoint, then routing is mostly mechanical.

Ground, Mast, or Conduit?

On the Ground

Fine mechanically if you protect it from UV, abrasion, and lawn equipment. RF-wise, ground contact does not automatically fix common-mode / stray return RF current.

Strapped to a Mast

Mechanically tidy and useful for strain relief. RF-wise: on dipoles and vertical dipoles with a feedpoint choke it is usually fine. On EFHW or OCF installations, if common-mode / stray return RF current is present, the mast can become part of the radiating system.

In Conduit

Excellent mechanical protection and makes future replacement easier. On HF it will not hurt normal coax operation. If the coax is radiating, conduit may change coupling slightly, but the real fix is still: choke plus defined return path.

Symptoms Your “Routing Problem” Is Actually an RF Problem

If you see any of these, you are dealing with common-mode / stray return RF current, not bad coax:

• SWR changes when you touch or move the coax.
• SWR changes a lot with different coax lengths.
• RFI in the shack: hot mic, buzzing speakers, computer glitches.
• Your antenna “works better” when coax is laid out in a certain shape.
• Receive noise changes dramatically depending on where coax runs inside the house.

Fix List, in Order

1. Add or upgrade a feedpoint choke/current balun appropriate to the antenna type.
2. Add a choke at the shack entrance if RF is coming back indoors.
3. Improve the antenna’s return path with radials or counterpoise where needed.
4. Then tidy up routing or burying for mechanical reasons.

A Simple Install Checklist for HF

Before You Bury Anything

• Get the antenna working and stable first.
• Confirm SWR does not change wildly when you move the feedline near the feedpoint.

At the Feedpoint

• Dipole / vertical dipole: 1:1 current balun or choke at the feedpoint.
• OCF: transformer as designed plus strong choking.
• EFHW: decide on counterpoise strategy; choke accordingly.
• Vertical: radials/counterpoise plus optional choke at the base.

On the Run to the Shack

• Leave the antenna area cleanly; do not run parallel to radiators.
• Route away from house wiring when possible.
• Add a choke at the shack entrance if needed.

At the Shack Entry

• Use an entry panel if possible and bond/ground appropriately for lightning safety.
• Weatherproof any external fittings and use drip loops.

The Takeaway Rules of Thumb

• Balanced antenna + good choke = coax routing is mostly mechanical.
• Unbalanced antenna without a defined return = coax routing becomes part of the RF design unless you control common-mode / stray return RF current.
• Bury coax for protection and neatness, not as an RF cure.
• If coax length changes SWR a lot, do not hunt the “magic length”... hunt common-mode / stray return RF current.

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