Best Feedline for HF Vertical Antenna | Greyline Kits

The Signal Lab · Feedline Doctrine

Complete Feedline System Kits

Every Greyline VDA is a complete antenna. What connects it to your shack is a system, and that system has to be configured correctly for the antenna to perform. This page specifies three complete feedline configurations: 450-ohm ladder line (lowest loss under high SWR, aerial installation), coaxial cable (simplest permanent installation, buriable), and silicone HV wire in metallic flex conduit (lower loss than coax under high SWR, buriable, cost-effective). All three work. Choose by site, run length, and operating preference. Every dB counts.

Read this first: tuner for the match, choke for the common mode

New operators often see "450-ohm ladder line" and "50-ohm coax" and conclude the system needs a 9:1 (or 4:1) transformer to match them. It does not. The 450 ohms printed on ladder line is the line's characteristic impedance, not the impedance your antenna presents. A multiband antenna shows a different impedance on every band, so no fixed ratio describes it, and no fixed 9:1 or 4:1 can match it — a transformer only moves the mismatch somewhere else and adds its own loss.

Two devices, two jobs. The tuner does the matching, band by band, to the 50 ohms your radio wants. The 1:1 choke keeps RF off the outside of the feedline — at the feedpoint, or, with a remote tuner at the antenna, on the radio side of the tuner. That is the whole feed system, and every configuration below is built on it.

What is already in your box

Every Greyline antenna ships with its feed system: a short run of ladder line that lives inside the pole from the feedpoint to the base, five snap-on ferrites that make the 1:1 choke, a ladder-line to PL-259 adapter, and spacers. Most owners use the adapter at the base to join coax and run it to the tuner; the three kits below are the options for that run. Common is not always most efficient, so compare them for your length and bands in the Feedline Loss Calculator first. Nothing on this page is required to get on the air. The three kits are configurations — advice on the run from the antenna to the shack — not products. Chokes by power rating are on the site for stations running an amplifier or wanting headroom, and assembled coax and hardline runs are on the shelf if you would rather not build your own.

The Science Behind the Kit

Why the VDA Has Specific Feedline Requirements

The VDA feedpoint is elevated and positioned off-center along the radiator, not at the midpoint. This is what makes the antenna multiband and radial-independent. It is also what makes feedline management important.

In a perfectly center-fed dipole, the two legs are equal and the feedpoint currents are equal and opposite, so the feedline is inherently balanced. In an off-center fed antenna the two legs are unequal, and the feedpoint currents are not perfectly equal on every band. That imbalance — which varies by frequency and feedline length — is the source of common-mode current on the feedline.

What is common-mode current?

A feedline — ladder line or coax — is meant to carry two equal and opposite currents, the differential mode that delivers power to the antenna. Common-mode current is the unequal component: it flows on the outside of the coax shield, or on both ladder-line conductors in phase. It travels down the feedline toward the shack, causing noise on receive, RF feedback on transmit, erratic tuner behavior, and at high power, equipment problems and RF burns. Rauch W8JI documents it thoroughly: when the outside of the shield carries current, it becomes part of the antenna.

The solution in every feedline path is the same in principle: a high-impedance 1:1 current choke wherever common-mode current would otherwise flow freely. In the ladder-line configuration that means two chokes — one at the feedpoint where the imbalance originates, one at the wall where balanced line meets coax. In the coax configuration it means one choke at the feedpoint, so the coax braid never becomes part of the antenna — or, with a remote tuner at the antenna, one choke on the radio side of the tuner.

The key principle: for an OCF antenna, the choke at the feedpoint is the primary one. A choke only at the shack wall is better than nothing, but the feedline between the antenna and a wall-only choke can behave as part of the antenna on certain bands. That is why some bands feel different from others in an under-choked OCF installation. The feedpoint choke stops the problem at the source.

A note on power levels: at 100 watts you may not notice common-mode problems at all. Add a linear amplifier and the same system can develop RF in the shack, tuner drift, and computer crashes. Common-mode current scales with power, and so does the choke impedance required to suppress it. The antenna itself comfortably handles the full legal limit; the choke and tuner set the system’s rating. The kits below are specified for legal-limit power. At 100 watts, the 500W-rated choke is sufficient; at a kilowatt or more, use the 3500W or 5kW options.

Kit 1 — 450-Ohm Ladder Line System

Lowest possible feedline loss — two chokes required, one optional

Best for: operators willing to manage a two-choke system in exchange for lower feedline loss under high-SWR multiband conditions. Open-wire balanced line has almost no dielectric loss — only conductor losses — and outperforms coax on the bands where the VDA presents elevated SWR, particularly on longer runs and the low bands. This is the choice for the serious DX station where feedline efficiency matters and aerial routing is practical. Requires a wide-range tuner.

Routing note: 450-ohm ladder line cannot be buried. Route it through the air, away from metal structures, and parallel to the antenna by at least 12 inches wherever possible. Where it must pass close to metal or walls, keep the run short and maintain spacing. Ice loading is a consideration in northern climates.

Component 1-A — Wall transition choke (required)

1:1 current choke, balanced studs in, SO-239 out

Spec: 1:1 current choke · rated for your power · 1.5–54 MHz · weatherproof housing

What it does: Manages the balanced-to-coax transition at the shack wall, presenting a high common-mode impedance to current trying to flow on the outside of the coax braid. Without it, the braid becomes a third conductor — an unintended antenna radiating back into the shack.

Why 1:1, not a 4:1 or 9:1: The impedance on the ladder line changes from band to band on a non-resonant antenna. No fixed transformer can match it; the wide-range tuner exists to do exactly that job. A 1:1 current choke does the one job this transition needs — stopping common-mode current — without adding a transformation the tuner did not ask for.

Placement: Outside the shack wall, at the point where the ladder line arrives. Connect the two ladder-line conductors to the balanced studs. Run the shortest possible coax from the SO-239 into the shack. Weatherproof.

Component 1-B — Antenna feedpoint choke (required)

Greyline feedpoint choke — included with every antenna; upgrade by power

1:1 current choke · ships in your box · higher ratings: the 3500W Maxi and the 5kW beads

What it does: Chokes common-mode current at the source, before it can travel down the ladder line toward the shack. This is the most important choke in the system for an OCF antenna.

Why feedpoint placement is primary: The feedpoint is where the current imbalance originates on some bands. The feedline between the antenna and any downstream choke can itself act as part of the antenna on certain frequencies, making a wall-only choke less effective there. A choke at the feedpoint stops the problem at its origin.

Placement: At the antenna feedpoint connections, between the feed studs and the ladder-line conductors.

Any equivalent 1:1 current choke rated for your power and 1.5–54 MHz does the same job. Call us if you are unsure which rating you need.

Component 1-C — Station entry choke (optional, recommended at amplifier power)

Greyline Maxi Line Isolator, or any 5kW 1:1 coax current choke

1:1 current choke · coax in/out · 3500W Maxi

What it does: A second choke on the coax run between the wall choke (1-A) and the tuner, a second line of defense against residual common-mode current inside the shack. At legal-limit power with an amplifier, a meaningful addition.

Placement: Between the short coax from Component 1-A and your tuner input, inside the shack or just outside the entry point.

Wiring diagram — signal path, Kit 1

VDA antenna (elevated OCF feedpoint)
↓ feed studs
1-B — Greyline feedpoint choke [1:1 at the feedpoint]
↓ 450-ohm ladder line (through the air, away from metal)
1-A — 1:1 current choke [wall transition — balanced studs in, coax out]
↓ shortest possible 50-ohm coax (LMR-400 class minimum)
1-C — Greyline Maxi or equivalent [optional station entry — 1:1]
↓ coax to tuner input
ANTENNA TUNER (wide-range — this is where the match happens)
↓
AMPLIFIER (if used)
↓
RADIO

Setup sequence — Kit 1

1. Install Component 1-B at the antenna feedpoint before any RF is applied.
2. Route the ladder line from feedpoint to shack wall, clear of metal.
3. Install Component 1-A at the shack wall exterior.
4. Run the shortest possible coax from 1-A to the tuner input. Install 1-C here if using it.
5. First session: 20 meters, 100 watts maximum. Tune. If the tuner tunes 20, work outward from there.
6. Check for RF feedback: touch the mic, the key, the computer — no tingle means clean.
7. If specific bands behave differently (won't tune, noisy, feedback), note which ones; the pattern tells you which choke position needs attention or upgrading.
8. Once clean at 100W, work up through the bands.
9. Add the amplifier last, at reduced power first, band by band.

Total investment — Kit 1: the feedpoint choke ships with the antenna; add a 1:1 wall choke rated for your power, and optionally a station-entry choke. Choose the 3500W or 5kW ratings for amplifier operation.

Kit 2 — Coaxial Cable System

Lowest complexity — one component required, one optional

Best for: operators who want a clean, permanent, buried installation with no feedline management — one cable from the antenna base to the shack. Coax loses more than open wire at elevated SWR, and that loss grows with run length and frequency; on short runs with quality low-loss cable it is small, and with a remote tuner at the antenna the coax sees a near-perfect match and most of that loss disappears. With a kilowatt-class amplifier, a coax-fed Greyline is a formidable station.

Component 2-A — Antenna feedpoint choke (required)

Greyline RF Choke / Line Isolator — choose by power

1:1 current choke · SO-239 in/out · 1–61 MHz · 500W Mini · 3500W Maxi · 5kW slip-on beads

What it does: Stops common-mode current at the antenna feedpoint, so the coax outer braid never becomes a third conductor and an unintended radiator. Without it, RF travels down the outside of the shield into the shack: noise on receive, RF feedback on transmit, equipment problems at high power.

Which rating: 500W for a barefoot station, the 3500W Maxi for an amplifier, the 5kW beads for legal limit with margin. Rate the choke above your amplifier's peak, not at it.

Placement: At the antenna feedpoint, coax side — the first device the coax meets when it leaves the antenna. Mount it securely at the base of the mast. Weatherproof.

Remote tuner at the antenna? Then the tuner sits at the base and the choke goes on the radio side of the tuner — the coax behind the tuner runs matched to the shack, and the choke keeps it clean. The same rule holds for any choke design.

Component 2-B — Station entry choke (optional, recommended at amplifier power)

A second Greyline choke, matching the rating of 2-A

What it does: A second choke at the shack entry, between the incoming coax and the tuner input. Catches residual common-mode current picked up along the run. Optional at 100 watts; add it at a kilowatt.

Coax selection guide

Cable Run length Power Notes
LMR-400 class Up to 100 ft Up to 1.5 kW Minimum recommended. Direct-burial versions available.
LMR-600 class Any length Legal limit Recommended for permanent buried runs. Lower loss, handles full power cleanly.
Hardline Long runs Any Best possible. Contest and commercial stations use it.

Rather not build it yourself? We stock assembled runs in genuine Times Microwave LMR-400 and LMR-600 and Andrew Heliax hardline — cut to length, terminated, weatherproofed, and labeled. Stock lengths 25 to 100 feet; longer runs quoted. Ten percent comes off the feedline when it rides with an antenna, and it ships free with the antenna. See the coax line →

PVC-jacketed coax is not recommended for permanent outdoor or buried HF runs: UV and moisture degrade it over time. Use polyethylene-jacketed, direct-burial-rated cable.

Wiring diagram — signal path, Kit 2

VDA antenna (elevated OCF feedpoint)
↓ feed studs
2-A — Greyline RF Choke [1:1 at the feedpoint — or radio side of a remote tuner]
↓ LMR-400 class minimum / LMR-600 class recommended (direct burial)
2-B — second Greyline choke [optional station entry — 1:1]
↓ coax to tuner input
ANTENNA TUNER (this is where the match happens)
↓
AMPLIFIER (if used)
↓
RADIO

Setup sequence — Kit 2

1. Install Component 2-A at the antenna feedpoint — or on the radio side of a remote tuner — before any RF is applied.
2. Run coax from 2-A to the shack. Bury it if possible, in direct-burial-rated cable.
3. Install Component 2-B at the shack entry or tuner input (optional, now or later).
4. First session: 20 meters, 100 watts maximum. Tune, then work outward band by band.
5. Check for RF feedback. No tingle means a clean installation.
6. Work through the bands at 100W, then add power. Amplifier last.

Kit 3 — Two-Conductor HV Silicone Wire in Metallic Flex Conduit

Lower loss than coax under high SWR — buriable — cost-effective — requires installation care

Two silicone-insulated high-voltage wires run inside metallic flexible conduit. The conduit shields the balanced pair, the silicone is an excellent dielectric for HF, and the whole assembly can be buried. Under the high-SWR conditions a multiband non-resonant antenna presents on most bands, this configuration loses less power than coax — and costs less per foot to install.

The configuration follows standard transmission-line physics. Zavrel's Antenna Physics: An Introduction (ARRL) ranks the common wire insulations: silicone rubber is the best practical choice for a buried balanced line — excellent voltage breakdown, adequate loss tangent into the VHF range, reasonable flexibility and cost — while Teflon (PTFE) is better on loss tangent but prohibitively expensive. The balanced-line geometry is consistent with Kraus (Antennas, McGraw-Hill) and the ARRL Handbook treatment of open-wire feedlines.

Why not PVC wire insulation?

Two reasons. Most PVC-insulated wire is not rated for the high voltages on a feedline at elevated SWR and full power. And PVC has a poor loss tangent at RF: it absorbs a measurable fraction of the energy as heat. At 60 Hz that loss is negligible, which is why PVC is fine for household wiring; at HF it is not. Silicone rubber avoids both problems.

Component 3-A — Wire (required)

Silicone rubber-insulated 2-conductor wire — #16 AWG minimum, #14 AWG preferred — high-voltage rated

Search: "silicone mini split wire 2-conductor" or "16 AWG silicone high-temperature 2-conductor" — electrical suppliers. A voltage rating of several thousand volts is required.

Wire gauge: #16 AWG is the minimum; #14 AWG reduces conductor resistance on longer runs.

Component 3-B — Conduit (required)

Metallic flex conduit with PVC jacket — ½" or ¾" ID

Flexible metallic conduit with attached PVC jacket — any electrical supplier or home center — about $0.75–$1.25/ft.

Why metallic conduit: Burying a balanced line directly in soil lets soil conductivity and moisture alter the line's impedance and add loss. The metallic conduit shields the pair from the soil; the outer PVC jacket weatherproofs it for direct burial.

Size: ½" ID for two #16 AWG conductors; ¾" for #14 AWG or runs with multiple bends. Separate metal conduit inside non-metallic conduit also works, at lower material cost.

Component 3-C — Shack-end transition (required)

Balanced-line tuner — or a 1:1 current choke at the wall

Two paths work. If your tuner has balanced output terminals, the wire runs directly to them — the Johnson Matchbox is the classic example of an excellent balanced-line tuner. If your tuner has coax only, a 1:1 current choke at the wall (same spec as Kit 1, Component 1-A) handles the transition. Not a 4:1 or 9:1: the tuner does the matching. See Do I need an antenna tuner? for the tuner options.

Why lower loss than coax under high SWR — the physics

Coax at elevated SWR loses more than its matched-load specification says, and the extra loss grows with SWR and run length. A balanced line with low-loss insulation has conductor losses and almost no dielectric loss, so under high SWR it loses substantially less than equivalent coax. This is standard transmission-line physics, consistent with Kraus and the ARRL Handbook loss tables.

The metallic conduit solves the one problem that makes buried open wire impractical — soil coupling — giving a balanced line the burial characteristics of coax while keeping its loss advantage.

Wiring diagram — signal path, Kit 3

VDA antenna (elevated OCF feedpoint)
↓ feedpoint studs to wire conductors
Two silicone HV wires inside metallic flex conduit
   (buried run — stable impedance regardless of soil)
↓ conductors emerge at shack entry
3-C — balanced tuner terminals [direct] OR 1:1 current choke [balanced in, coax out]
↓
ANTENNA TUNER → AMPLIFIER (if used) → RADIO

Installation notes

1. Pull both conductors through the conduit before burial; use pulling lubricant on longer runs.
2. Leave 18–24 inches of wire at each end for connections.
3. Seal the conduit ends with weatherproof silicone sealant.
4. Mark conductor polarity at both ends before burial and keep it consistent.
5. Connect the conductors to the VDA feedpoint studs; weatherproof with self-amalgamating tape.
6. At the shack end, connect to balanced tuner terminals or to the balanced studs of a 1:1 current choke.
7. Bury at least 6 inches deep, 12 inches preferred.

Kit 3 vs. Kit 2 (coax): Under the high-SWR multiband conditions of a VDA installation, Kit 3 has lower feedline loss and lower material cost per foot than coax, and can be buried permanently. The trade-off is installation discipline. For short runs at modest power the difference is small and coax is simpler; for long permanent runs at full power, the physics favors Kit 3.

Which Kit Is Right for You?

Choosing Between Them

Factor Kit 1 — Ladder Line Kit 2 — Coax Kit 3 — HV Wire / Conduit
Feedline loss Lowest under high SWR — advantage on long runs and low bands Higher than open wire under high SWR; small on short runs Lower than coax under high SWR
Can be buried? No Yes — direct-burial coax Yes — metallic conduit with PVC jacket
Complexity Two chokes, aerial routing discipline, weather-sensitive One choke, bury and forget — simplest Wire pulling, polarity tracking, weatherproof connections
Ice / weather Exposed aerial run — ice loading; rain shifts the match slightly (the tuner corrects) Buried, no exposure Buried, no exposure
Tuner requirement Wide-range tuner Standard desktop or remote tuner works Wide-range tuner; balanced output preferred
Best for Aerial runs where burial isn't possible; maximum low-band performance Permanent buried installation — simplest, most reliable Long buried runs at high power where feedline loss matters

Most owners — including many RF engineers — default to Kit 2 (coax): permanent, reliable, plug-and-play. But the common choice is not always the most efficient one for a given run. Kit 3 earns its place on long buried runs at high power. Kit 1 is for the operator who wants the lowest loss on an aerial run and will manage the discipline that comes with it. All three work; which loses least on your run is a calculation, not an opinion — put your length and bands into the Feedline Loss Calculator and let the numbers decide. The antenna, the location, and the operator are what make DX happen.

The Shelf Behind It

Every component spec on this page traces to the standing references in transmission-line and RFI engineering: Maxwell W2DU on transmission lines, Brown K9YC on RFI and ferrites, Severns N6LF on ground systems, Rauch W8JI on common-mode current, Lewallen W7EL on baluns, Kraus W8JK (Antennas), Zavrel (Antenna Physics, ARRL), and the ARRL Handbook. The Shelf We Read From →

Ham Radio is fun again! Pass it on… 73, Jon KL2A · 435-200-4902