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Technical Note No. 2.2.1

Feed System Configuration: Tuner, Choke, and Coax Setup

Physics of the feed point

A Greyline VDA is an off-center-fed vertical dipole, and the pole itself is the antenna. It operates without a radial field because both halves of the dipole are above ground — the antenna floats electrically. Correctly configured, the feed system preserves that isolation and lets the tuner present a matched load across the full operating range.

Configuring the Tuner and Choke

A common assumption is that every antenna system needs an RF ground connection at the tuner. For the Greyline VDA, that assumption is wrong. Both the upper and lower radiator sections are electrically isolated from earth, and the off-center feed point wants a balanced, choked feed to work correctly. (Your station itself is still grounded for safety, per the ARRL’s recommendations — that is a separate job from RF.)

A tuner in the shack and a remote tuner at the antenna both work, and both are common on Greyline stations — RF engineers run each.

Two accepted configurations:
1. Shack tuner: Radio → ATU → Coax → 1:1 Choke at the feedpoint → Antenna
2. Remote tuner: Radio → Coax → 1:1 Choke → Remote ATU at the antenna → Antenna

That is the whole rule for any choke design: the choke goes at the feedpoint — unless a remote tuner sits at the antenna, in which case it goes on the radio side of the tuner.

If you are starting fresh, the antenna + remote ATU bundles arrive spec'd together — and the standalone tuners live in the antenna tuner collection.

The floating balanced output

Most modern tuners have an unbalanced output — the coax shield is grounded internally. To present a floating, balanced drive to the dipole, place a 1:1 current choke per the rule above. It suppresses common-mode current on the coax shield and keeps RF off the feedline’s outer conductor. Never a 4:1 or a 9:1 — a vertical dipole wants isolation, not transformation. The tuner does the matching.

Build sequence — antenna through feed system

1. Ground section. The lower section sets in the PVC sleeve. No RF connection to earth is required.
2. Feed point connection. The ladder line inside the pole connects to the two halves of the dipole at the feedpoint insulator. The conductor on the upper radiator carries through to the center pin of the PL-259 at the adapter.
3. Choke placement. Place the 1:1 current choke per the rule above. Mount a remote tuner at least 6 inches above grade — a PVC standoff or wooden stake both work.

Agency and municipal deployments

Configuring a system for a Sheriff's office, Fire EOC, or emergency management facility? Greyline provides full technical documentation and architectural briefs for municipal and agency installations.

Agency Solutions · Capabilities Statement

Technical references

• Your RF System, End To End
• Where the choke goes
• Current balun vs voltage balun
• RF balance — isolation vs. symmetry
• Do I need a tuner? Shack or remote
• Technical line: 435-200-4902

73, Jon KL2A — 435-200-4902

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