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 (protect the cable, avoid water ingress, avoid UV, avoid tripping hazards) and RF current control (stop 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 + intentional choking), coax routing becomes mostly a mechanical/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 (right angle if practical), then route wherever you want.

Why it matters: if there’s 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: don’t let the connector carry the cable weight.
• Drip loop before any enclosure/building entry: water follows the cable.

Weatherproof every outdoor connector properly

Outdoor coax failures are usually water ingress, not “RF issues.”

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

Add choking intentionally (don’t rely on “lucky routing”)

If you do nothing else: use a proper common-mode choke/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” is simply 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 “oops” 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/return system.

When to Bury Coax (And When Not To)

Bury coax when

• It’s a permanent or semi-permanent installation.
• You want protection from damage and UV.
• You want predictable routing and fewer mechanical failures.
• You’ve 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’re 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 haven’t controlled that yet.
• You would end up burying a splice/connector (avoid buried connectors).

Practical burying tips (ham-friendly)

• Use direct-burial rated coax if it’s 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 (Center-Fed): Coax Routing That Actually Matters

A center-fed dipole is balanced. Coax is unbalanced. If you connect coax directly, the dipole may still work, but it often invites Common-mode & Stray return RF current and 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: don’t 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/balun, burying is usually purely mechanical. A buried coax run feeding a well-choked dipole is common and stable.

OCF Dipoles (Off-Center Fed): Why Coax Routing Gets People in Trouble

OCF dipoles are popular because they can be multi-band 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.
• The currents on each side are different.
• Even with a balun, some Common-mode & Stray return RF current may remain.

Best-practice setup

• Use the recommended unun 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/wiring unless Common-mode & Stray return RF current is well-controlled.

The “coax length matters” myth (why people believe it)

With OCFs, changing coax length can change how Common-mode & Stray return RF current behaves, so SWR might shift when you add/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 (End-Fed Half-Wave): Where Most Coax Routing Confusion Comes From

EFHW antennas are intentionally unbalanced. They can work extremely well on HF, but their feed system needs a return path. If you don’t 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 (pick one on purpose)

Strategy A: Provide a defined return, then choke hard

• Add a dedicated counterpoise or radial system at the transformer/feedpoint ground.
• Use a common-mode choke right at (or very near) the transformer output to keep Common-mode & Stray return RF current off the coax.
• 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’s more sensitive to routing and environment.

Strategy C: No defined return, minimal choking

It may still make contacts, but it’s 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’ve decided your return/choking strategy.

Verticals: When Burying Coax Is Normal, and When It’s 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/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/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 doesn’t automatically “fix” Common-mode & Stray return RF current.

Strapped to a mast

Mechanically tidy and provides strain relief. RF-wise: on dipoles/vertical dipoles with a feedpoint choke it’s usually fine. On EFHW/OCF, 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 easy. On HF it won’t “hurt” coax operation. If the coax is radiating, conduit may change coupling slightly, but the real fix is still: choke + defined return path.

Symptoms Your “Routing Problem” Is Actually an RF Problem

If you see any of these, you’re 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/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 (radials/counterpoise) for unbalanced antennas.
4. Then tidy up routing/burying for mechanical reasons.

A Simple Install Checklist for HF

Before you bury anything

• Get the antenna working and stable first.
• Confirm SWR doesn’t change wildly when you move the feedline near the feedpoint.

At the feedpoint

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

On the run to the shack

• Leave the antenna area cleanly (don’t 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, don’t hunt the “magic length”... hunt Common-mode & Stray return RF current.

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