Build a 20 Meter Vertical Antenna
The 20m quarter-wave vertical is one of the most effective antennas an HF operator can build for worldwide DX. At just 16.5 feet tall it is short enough to install almost anywhere — a rooftop, a small urban lot, a deck, or even a portable mast for field use — yet it delivers a low-angle radiation pattern that consistently outperforms a horizontal dipole at modest heights for long-haul contacts. This guide covers the complete build from element sizing through radial installation, feedpoint assembly, and final tuning for 14 MHz operation.
Quarter-Wave Vertical Fundamentals at 14 MHz
The 20m quarter-wave vertical operates on exactly the same principle as the 40m vertical — one half of a dipole, with the ground plane providing the missing half electrically. The shorter wavelength at 14 MHz means the element is half the physical length of a 40m vertical, making installation far easier:
The shorter element at 20m is an advantage in almost every practical dimension — it is lighter, cheaper to build, easier to raise, and more forgiving mechanically. A single 20-foot length of aluminum tubing or a 20-foot fishing pole is all that is needed for the support structure.
20m vs 40m Vertical — Key Differences
Building a 20m vertical differs from the 40m version in a few important ways operators should understand before starting:
- Element is half the length: 16.5 ft vs 33 ft — far easier to support self-standing. A single section of 1.0-inch aluminum tubing handles the job without telescoping sections.
- Radials are half the length: 20m radials are ~16.5 ft each vs ~33 ft for 40m — the total copper required for 16 radials is half that of the 40m version, significantly reducing cost.
- Narrower bandwidth: the 20m band is 350 kHz wide (14.000–14.350 MHz). A quarter-wave vertical tuned to 14.150 MHz typically shows SWR below 2:1 across the entire 20m band without a tuner — good bandwidth coverage is not a challenge on 20m.
- More sensitive to nearby objects: at 14 MHz, the antenna's near-field extends roughly 5 feet from the element. Metal gutters, fences, or structures within 5 feet cause more significant detuning than they would on 40m. Keep clear of metal objects within 5–8 feet of the element.
- Excellent rooftop and portable candidate: the compact size makes it practical to mount on a rooftop with elevated radials, a deck railing, or a portable tripod mast.
Radiation Pattern and DX Performance
The 20m band is the premier DX band for most of the solar cycle — it supports worldwide propagation reliably during the day on most days of the year. The vertical's low radiation angle is especially valuable on 20m:
The 20m vertical shines for operators who cannot get a dipole above 30 feet. Against a dipole at 50–66 feet the contest becomes closer, and at λ or higher the high dipole becomes competitive or superior. But for the typical suburban installation with a dipole at 25–35 feet, the vertical is the better DX antenna by a meaningful margin.
Element Construction Options
Three practical approaches, all well-suited to the shorter 20m element:
- Single aluminum tubing section: a single 20-foot length of 1.0-inch OD 6061-T6 aluminum tubing handles the 16.5-foot element with no telescoping required. Clean, rigid, and permanent. This is the simplest aluminum construction possible — one piece of tube, one base mount.
- Telescoping aluminum (two sections): a 1.25-inch OD lower section (10 ft) and a 0.75-inch OD upper section (8 ft) gives more flexibility in height adjustment and packs down for transport. Useful if the antenna will be occasionally relocated or stored.
- Fishing pole with wire: a 6-meter (20-foot) fiberglass fishing pole supports a #18 or #20 AWG copper wire element perfectly. Extremely lightweight and portable — ideal for travel, POTA, and SOTA activations where the 20m vertical is the workhorse antenna. Sets up in under 10 minutes from a small carry bag.
| Target frequency | Band segment | Element length (ft) | Element length (m) | Notes |
|---|---|---|---|---|
| 14.000 MHz | CW bottom | 16.71 ft | 5.10 m | Cut here for CW-only operation |
| 14.025 MHz | CW | 16.68 ft | 5.09 m | CW segment center |
| 14.074 MHz | FT8 / digital | 16.63 ft | 5.07 m | FT8 and FT4 calling frequency |
| 14.150 MHz | Phone center (recommended) | 16.55 ft | 5.05 m | Best all-band compromise — full 20m usable without ATU |
| 14.225 MHz | Phone center (ITU Region 1) | 16.46 ft | 5.02 m | Common phone calling frequency |
| 14.300 MHz | Maritime mobile / phone | 16.37 ft | 4.99 m | Upper phone segment |
| 14.350 MHz | Band top | 16.31 ft | 4.97 m | Upper band edge — not recommended as center |
Vertical 20m Calculator
Materials for a ground-mounted 20m quarter-wave vertical with 16-radial ground plane
What the NanoVNA Will Show
The 20m vertical feedpoint behaves identically to the 40m version in principle but with some practical differences due to the higher frequency and shorter element:
Rooftop and Elevated Installation Considerations
The compact 20m vertical is an excellent candidate for rooftop or elevated installations where a 40m vertical would be impractical. Key points for elevated mounting:
- Use elevated radials: on a roof or deck where on-ground radials are impossible, 4 elevated radials at λ/4 length (16.5 ft) perform almost as well as 16–32 on-ground radials. Extend them horizontally from the base in four directions, supported by the roof structure or lightweight mast arms.
- Height benefit on 20m: a 20m vertical at 30 feet above ground (rooftop) has its radiation pattern enhanced by the height — the effective take-off angle is even lower than a ground-mounted version. Rooftop mounting is genuinely beneficial for 20m DX.
- Metal roof interaction: keep the element base at least 3 feet above a metal roof surface. A metal roof within 2 feet of the element base significantly detunes the antenna and raises SWR. Use a non-conductive standoff mast to achieve this separation.
- Wind load: a 17-foot aluminum element in 1.0-inch OD tubing weighs approximately 1.5 lbs and presents modest wind load. A simple deck rail mount or rooftop tripod with two guy wires handles this easily.
Building the 20m Quarter-Wave Vertical
This guide builds a ground-mounted single-section aluminum tubing vertical with a 16-radial on-ground system. Notes for fishing-pole and elevated installations are included at relevant steps.
Select the Site and Plan Radial Layout
Choose a site with at least 17 feet of clear ground in all directions from the element base for the radial system. Unlike the 40m vertical, the 20m radials are short enough that even a modest suburban lot can accommodate a full 16-radial system. Key site criteria:
- Clear of metal structures within 8 feet: at 14 MHz the antenna's reactive near-field is smaller than at 7 MHz, but metal fences, gutters, or downspouts within 5–8 feet still cause measurable detuning and pattern distortion.
- Coax exit at 90°: plan the coax route so it leaves the feedpoint perpendicular to the element for the first 10 feet before turning toward the shack. On 20m this separation is more critical than on 40m — the higher frequency means the coax couples more readily to the element at short distances.
- Rooftop option: if a ground installation is not possible, the 20m vertical is small enough to mount on a roof tripod or chimney mount with 4 elevated radials. See the elevated radial section later in this guide.
Cut the Aluminum Tubing Element
Cut the 1.0-inch OD aluminum tubing to 17.5 feet (210 inches) — longer than needed to allow trimming to exact resonance. Use a tubing cutter for a clean square cut; deburr both ends inside and out with a round file. A single 20-foot section purchased from a metal supplier or hardware store provides the element plus a few inches of offcut for the trim allowance.
Install the Base Mount and Feedpoint Assembly
Install the base mount at the chosen site. The 20m element is light enough that a simpler mount than the 40m version suffices — a fence post anchor driven 18 inches into the ground with a PVC or nylon coupling at the top handles a 17-foot 1.0-inch aluminum element with ease. A homebrew mount of 4-inch PVC pipe set in a small concrete footing is also more than adequate.
Mount the SO-239 feedpoint connector at the element base. Drill a 5/16-inch hole through the aluminum element 2 inches from the bottom end. Insert a stainless steel bolt through the hole with a ring terminal — this is the center-conductor connection point. The SO-239 mounts to a small aluminum bracket clamped to the element base, with the center pin connecting to the ring terminal bolt and the shell connecting to the radial hub directly below.
Install the Radial Hub and Run 16 Radials
Install a copper radial plate or bus bar at the base of the element, directly connected to the SO-239 shell. Cut 16 radial wires of #14 AWG copper at 17.5 feet each — slightly longer than the element for a small trim allowance. Crimp a ring terminal on one end of each radial and bolt all 16 to the radial hub. Space evenly at 22.5° intervals.
Lay the radials on the ground surface and stake them flat with garden staples every 6 feet. The shorter 20m radials fit easily in a typical suburban back garden without reaching fences or structures. For installations where even 17-foot radials cannot be accommodated in all directions, use shorter radials in the constrained directions — a radial at 10 feet contributes meaningfully even if it is not full length.
Raise the Element and Connect Coax
A 17-foot single-section aluminum element is light enough for one person to raise alone — slide the element into the base mount sleeve and secure it with the mount's locking hardware. No gin pole or second person is required at this height and weight, though a second person makes the job easier and safer.
Connect the coax: PL-259 to SO-239 at the feedpoint, center pin to element, shield to radial hub. Install the current choke immediately at the feedpoint — wind 5–6 turns of coax through an FT-240-31 toroid and cable-tie it to the base mount. Route the coax away from the element base at 90°.
Weatherproof the SO-239/PL-259 connection with self-amalgamating tape — two full spiral layers from below the connector shell up over the junction and back down.
Initial SWR Measurement
Connect the NanoVNA at the shack end of the coax. Sweep 13.0–15.5 MHz and locate the SWR minimum.
Trim to Resonance
Lower the element and trim from the top end to raise the resonant frequency to the target. Calculate the trim amount:
Repeat until the SWR minimum falls at or within ±30 kHz of the target. Final SWR at resonance should be below 1.5:1. Mark the final trimmed length on the element with a permanent marker.
Verify Full Band SWR and Document
Weatherproof all connections with self-amalgamating tape and RTV sealant at the base. Photograph and document the final element length, SWR at resonance, and SWR at band edges. Install a ground rod adjacent to the element base and connect it to the radial hub with #6 AWG bare copper wire for DC lightning protection. Install a coax lightning protector at the shack entry point.
4 Elevated Radials for Rooftop Installation
The 20m vertical is the most practical HF vertical for rooftop installation. The short element (16.5 ft) and short radials (16.5 ft) make the complete antenna fit on a typical residential rooftop with a simple tripod mount:
- Radial length: 16.5 ft each — same as the element. Cut 4 radials of #16 AWG insulated wire at 17 ft each and trim to resonance after installation.
- Radial orientation: run the 4 radials outward from the element base horizontally in four cardinal directions. Support each radial with a lightweight nylon cord tied to the rooftop structure or a small standoff at the end of each radial.
- Height above roof surface: keep the element base and radials at least 2–3 feet above the roof surface — proximity to roofing materials (especially anything with foil backing or metal) detunes the antenna.
- Performance: 4 elevated radials at 16.5 ft height (for a rooftop at ~20 ft above grade) provide excellent efficiency — better in practice than 8–12 on-ground radials in the same installation location due to the added height benefit.
Portable 20m Vertical — Field Deployment
The 20m quarter-wave vertical is the most popular antenna for POTA and SOTA activations. A complete portable kit weighs under 3 lbs and deploys in under 15 minutes:
- Element: 6-meter fiberglass telescoping fishing pole with #18 AWG wire taped along the outside. Collapses to 24 inches for transport.
- Radials: 4 × 17 ft lengths of #24 AWG stranded copper wire wound on a small plastic card. Each radial deploys in 30 seconds, laid on the ground in four directions from the feedpoint.
- Feedpoint enclosure: a small weatherproof project box with an SO-239, the current choke toroid, and terminals for the 4 radials. The fishing pole base slides into a PVC stub on the box top; the coax plugs into the SO-239 on the side.
- Support: the fishing pole is self-supporting in calm conditions. In wind, a single lightweight guy rope from mid-pole to a tent peg at 45° stabilizes it adequately.
- Performance: a 4-radial portable 20m vertical with 100mW is regularly worked across continents on FT8 during good band conditions. At 5W SSB it is a fully functional DX antenna.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| No SWR dip visible across 13–15 MHz | Feedpoint connection fault or coax polarity reversed | Check DC resistance from coax center to shield at radio end — should be open circuit | Verify center pin to element, shield to radial hub; check for coax short at connectors |
| SWR minimum is very broad — over 500 kHz wide | High ground resistance — too few or too-short radials | On 20m a good radial system produces a sharp SWR dip; broad curve means high ground loss resistance | Add more radials or extend short radials to full λ/4 length |
| Resonance shifts 100+ kHz between morning and afternoon | Metal structure nearby heating and expanding, or loose element base joint | Measure SWR at same frequency morning and evening; check all connections for looseness | Move antenna away from metal structures; tighten base mount; secure element in mount |
| SWR correct but strong RFI on receive — high noise floor | No current choke — coax acting as vertical radiator and picking up noise | Key up at low power and touch the coax near the radio — RF present on outside of coax confirms the issue | Install FT-240-31 current choke at feedpoint — 5–6 turns of coax through core |
| Resonance 200+ kHz too high after trimming | Element trimmed too short | Measure element — shorter than target length confirms over-trimming | Splice a short extension onto the element tip using a sleeve coupler; re-trim to resonance |
| SWR increases in rain or wet conditions | Water ingress at feedpoint connector | Dry the feedpoint and re-measure — improvement confirms water ingress | Strip and re-weatherproof feedpoint with self-amalgamating tape and RTV sealant |
| Element leans in wind | Base mount insufficiently anchored or element too heavy for single-point support | Check stake depth; check mount clamping hardware | Drive stake deeper; add a single guy wire from element mid-point to a ground stake at 45° |
| Good SWR but signal consistently weak vs other 20m operators | Inadequate radial system degrading efficiency | Check WSPR spots vs nearby operators with similar power and antenna type | Add radials — aim for 16 minimum, 32 for best performance; check current choke is installed |
Can I use a 20m vertical on other bands without a tuner?
A 20m quarter-wave vertical has a natural second resonance on 10m at approximately 28.3–28.5 MHz — three times the fundamental frequency — with SWR typically below 2:1 for a direct 50 Ω coax feed. This makes the 20m vertical a direct-feed dual-band antenna for 20m and 10m. On 15m (21 MHz) the antenna is 3/8-wave — SWR is moderate (typically 2–4:1) and the radio's internal ATU handles it. On 17m (18 MHz) and 12m (24 MHz) the SWR is higher and a tuner with reasonable range is needed. On 40m and 80m the antenna is electrically very short — a wide-range tuner handles it but efficiency is significantly reduced.
How many radials do I need for the 20m vertical?
The same rules apply as the 40m vertical — more is always better, with the largest improvements in the first 8 radials. Because 20m radials are only 16.5 feet long, installing 16 or even 32 radials is far less demanding in terms of wire cost and garden space than the equivalent 40m system. A reasonable minimum for a permanent installation is 8 radials; 16 is good; 32 is excellent. For a portable or temporary activation, 4 radials on the ground surface produce a fully functional antenna — not maximum efficiency, but more than adequate for QRP and low-power operation.
Is a 20m vertical better than a 20m dipole for DX?
Against a dipole at typical suburban heights (20–35 feet), yes — the vertical's low-angle radiation advantage is clear and consistent. Against a dipole at 50 feet the contest is much closer. Against a dipole at 66 feet (half-wave height) or higher the high dipole becomes competitive and may actually outperform the vertical during certain propagation conditions. The practical conclusion: if your dipole is below 40 feet, the vertical is the better DX antenna. If your dipole is at 50 feet or higher, the difference is small enough that personal preference, noise environment, and operating mode determine which is better for your specific station.
Can I mount a 20m vertical on my roof?
Yes — a rooftop 20m vertical is an excellent installation. The short element (16.5 ft) and lightweight construction make it easy to mount on a rooftop tripod or chimney bracket. Use 4 elevated radials extending horizontally from the element base at the rooftop level. Keep the element base at least 2–3 feet above the roof surface to reduce interaction with roofing materials. The added height of a rooftop installation (typically 20–30 feet above grade) genuinely improves the vertical's DX performance by further lowering the effective radiation angle. Verify that HOA rules and local building codes permit rooftop antenna installations before proceeding.
What coax length works best for a 20m vertical?
With a properly installed current choke at the feedpoint, coax length is not electrically critical for a 20m vertical — the choke isolates the antenna from the feedline and prevents the coax length from affecting resonance. Use whatever length is needed to reach from the feedpoint to the radio comfortably. For loss minimization, use LMR-400 for runs over 50 feet. For shorter runs, RG-8X is adequate and significantly easier to handle. Avoid RG-58 for any run longer than 30 feet at 14 MHz — its loss at this frequency is high enough to noticeably reduce transmitted and received signal levels.
How do I build a portable 20m vertical for POTA activations?
The simplest effective portable 20m vertical: a 6-meter fiberglass telescoping fishing pole with #18 AWG stranded copper wire taped along the outside, connected at the base to a small feedpoint enclosure containing a 49:1 UNUN or a simple SO-239 with a current choke. Four wire radials at 17 feet each, wound on a small card for storage, deploy on the ground in four directions from the feedpoint. The entire system fits in a daypack and weighs under 2 lbs. A small NanoVNA verifies resonance after deployment — trim the wire element to 16.5 ft before the first deployment and it will be on-frequency at every activation thereafter. Many POTA operators rate this as the single most effective antenna per pound carried.