Build a SOTA Vertical Antenna for Portable HF
Summits on the Air demands an antenna that sets up in under five minutes, fits in a rucksack alongside a radio and battery, survives wind and rain on a hilltop, and still makes the contacts needed to activate a summit. The linked quarter-wave vertical is the workhorse of the SOTA community — a single vertical wire with clip links that switch between bands, a handful of lightweight radials, and a fishing-pole mast that extends to 7 metres and folds to 60 cm. This guide builds the complete system from scratch.
Why a Vertical for SOTA?
On a summit there are no convenient trees at the right height and no room for a horizontal dipole at a useful elevation. The vertical antenna solves both problems — it needs only one mast, it radiates in all directions (essential when you do not know which direction your callers will come from), and its low-angle radiation pattern is actually enhanced on a hilltop where the ground slopes away from the antenna in all directions, extending the effective ground plane and lowering the take-off angle below what a flat-site vertical can achieve.
The linked vertical design — sometimes called the linked dipole when used as a vertical half-wave — uses a series of wire links that can be quickly opened or closed with crocodile clips or DIN connectors to change the electrical length of the antenna for different bands. A single antenna serves 40 m, 30 m, 20 m, and 17 m without an ATU, covering all four bands most commonly used for SOTA activations.
Quarter-Wave Vertical with Radials
The simplest design. One vertical wire at λ/4 length, three or four radials laid on the ground. Feed impedance approximately 35–50 Ω depending on radial count and ground quality. Requires an ATU or UNUN for a good 50 Ω match, or can be fed directly with acceptable SWR. Lightest possible system.
Linked Vertical Half-Wave
A half-wave vertical fed at the base through a 49:1 or 64:1 UNUN. Very high efficiency — no ground plane needed. End-fed half-wave (EFHW) design. Requires the UNUN transformer but eliminates radials entirely. Popular for summits where laying radials is impractical.
Inverted-L on a Mast
A single wire that runs vertically up the fishing-pole mast then bends horizontal at the top. More total wire = lower bands with a shorter mast. Useful for 40 m activation with a 7 m pole. Feed point at the base with radials. Good compromise between vertical height and overall wire length.
Linked Vertical Dimensions
The linked vertical uses a single wire for the longest band (40 m) with additional link points at the correct lengths for shorter bands. When operating on 20 m, the link clips at the 20 m section junction are opened, disconnecting the extra wire below and leaving only the 20 m length electrically active. The unused wire hangs free below the open link — it does not significantly affect the antenna's performance if it hangs vertically.
L (m) = 71.5 / f (MHz) — wire, K = 0.95 end-effect correction
| Band | Frequency (MHz) | Element length (m) | Cumulative from tip (m) | Link position from feed (m) |
|---|---|---|---|---|
| 17 m | 18.118 | 3.95 | 3.95 | 3.95 (tip — no link needed) |
| 20 m | 14.175 | 5.04 | 5.04 | 5.04 from feed |
| 30 m | 10.125 | 7.07 | 7.07 | 7.07 from feed |
| 40 m | 7.100 | 10.07 | 10.07 | 10.07 from feed (base) |
Link section lengths: the wire is cut in sections between links. Section from feed to first link (40 m section): 10.07 − 7.07 = 3.00 m. Section from first to second link (30 m section): 7.07 − 5.04 = 2.03 m. Section from second to third link (20 m section): 5.04 − 3.95 = 1.09 m. Top section (17 m tip): 3.95 m. These four sections are pre-cut and joined with links — open the links from the tip downward to select the active band.
SOTA Linked Vertical Calculator
Complete SOTA linked vertical system
Construction Sequence
Prepare the linked element and feed point, attach to the mast, cut the radials, then raise and tune. Practice the pack-down sequence at home before your first activation.
Prepare the element wire sections
Cut the four element sections to the lengths from the calculator. Label each section at both ends with a permanent marker and heat-shrink sleeve: T (tip/17m section), 2 (20m section), 3 (30m section), B (base/40m section). At each junction point, strip 30 mm of insulation, fold the wire back on itself, and crimp a ring terminal through the folded loop — this gives a solid mechanical attachment for the link clips without relying on solder joints that can fail in cold weather. Solder after crimping for security.
Build the feed point assembly
Mount an SO-239 chassis connector in the small weatherproof box. The box lid has a hole for the vertical element wire to exit at the top and holes for the radial wires at the bottom and sides. Inside, the SO-239 centre pin connects via a short wire to the vertical element terminal. The SO-239 outer connects to all four radial terminals. A coax choke (5 ferrite beads) threads onto the coaxial feedline immediately outside the box. Cable tie the feedline to the mast base for strain relief.
Attach element to mast
Starting at the mast tip, tape the wire tip with a small loop of insulating tape so it cannot slide. The wire runs down the outside of the mast, secured with a cable tie every 500 mm. At the link junction points, leave a short pigtail of wire (50 mm) dangling free for the link clip to attach to. The link clips hang off the element at each junction — when closed they carry current; when open they hang free. Keep the link assemblies tidy with a small rubber band around closed links to prevent them vibrating open in wind.
Cut and prepare the radials
Cut four radials each 10.1 m long (λ/4 for 40 m — the longest band used). Pre-wind each radial onto a small card bobbin or around two fingers and store in a small bag. On the summit, simply unwind and lay them on the ground radiating outward from the mast base. Do not worry about making them perfectly straight — a drooping radial over rocky ground still provides a useful ground plane. Clip each radial to its terminal on the feed point box.
Raise the mast
Raise the mast by extending sections from the base upward. On most 7 m fibreglass fishing poles, you extend one section at a time starting from the thickest (base) section. Anchor the base in a ground spike, rock crevice, or use a rucksack and two guy lines to hold it vertical. On very exposed summits, three guy lines at 120° intervals at 2/3 height keep the pole stable in moderate wind. Guy lines are pre-cut paracord with a loop at each end — 30 seconds to deploy.
Select band and check SWR
With all links closed the antenna is configured for 40 m. Connect a NanoVNA or the radio's built-in SWR meter (if available) and verify SWR is below 2:1 at 7.1 MHz. To switch to 30 m, open the lowest link (nearest the feed point). To switch to 20 m, also open the second link. To switch to 17 m, open all three links leaving only the top 3.95 m section active. On each band, the SWR should be 1.5:1 or better without an ATU. Minor trimming of the tip section during initial setup adjusts 17 m resonance, and the extra length folds back up the mast.
Pack-down sequence
Collapse the mast from the tip down, leaving radials and coax connected until the mast is fully collapsed. Remove radials (wind onto bobbins), disconnect coax. Open the element at each link and re-wind each section onto its bobbin. Total pack-down time: under 3 minutes with practice. The entire system — mast, element, radials, feed box, and coax — should fit in a stuff sack no larger than 30×10 cm and weigh under 400 g.
Mast Anchoring Without a Ground Spike
Rocky summits typically do not allow driving a ground spike. Instead, place the mast base in the best natural crevice available and brace it with three guy lines tied to rocks, trekking poles, or the rucksack. A simple method that works well: tie two guy lines to the mast at 1.5–2 m height, stake them at 120° with tent pegs or rock piles, then lean the rucksack against the base as a wind brace. This handles 30+ km/h summit winds reliably.
Radial Placement on Rough Ground
Ideal radials lie flat on the ground radiating symmetrically from the mast base. On rocky summits this is impractical — lay the radials in whichever directions the ground allows, even if they droop over edges or coil around rocks. Two radials are better than none; four radials are better than two. Studies of summit-mounted verticals show that even one draped radial provides 5–8 dB improvement over no ground plane at all, and the summit's natural elevated position compensates significantly for a poor ground system compared to a flat-ground vertical.
Operating in Rain and Wind
Water on the element wire shifts the resonant frequency down by 1–3% — the antenna becomes electrically longer. This is usually compensated by the radio's ATU if one is fitted. If not, the SWR rise is typically minor enough (below 2:1) to allow continued operation with most QRP transceivers. The link clips must be protected from water bridging them — wrap each closed link with a small piece of self-amalgamating tape if rain is expected. Open links should be held clear of the mast to prevent capacitive coupling through wet mast material.
EFHW Alternative — No Radials Needed
An increasingly popular alternative to the quarter-wave vertical with radials is the end-fed half-wave (EFHW) antenna used vertically on the mast. A half-wave wire for 40 m is approximately 20.4 m — longer than most fishing poles — so the EFHW is typically used for 20 m (10.2 m wire, fits on a 7 m pole with slight tilt at the tip) or 40 m as an inverted-L (7 m vertical, 13 m horizontal wire from the tip).
The EFHW requires a 49:1 or 64:1 impedance transformer (UNUN) at the feed point to match the very high impedance at the end of a half-wave wire (approximately 2,500–5,000 Ω) to 50 Ω coax. The transformer is a small toroidal winding — FT-140-43 core, 3 primary turns, 21 secondary turns for 49:1 — that can be built in an afternoon and weighs under 50 g. The EFHW system eliminates radials entirely, reducing pack weight and summit setup complexity, at the cost of slightly lower efficiency compared to a well-set-up quarter-wave vertical with four good radials.
| Band | Primary SOTA frequencies | Mode | Notes |
|---|---|---|---|
| 40 m | 7.032 (CW), 7.090–7.130 (SSB) | CW / SSB | Best for medium-distance chasers; good all day |
| 30 m | 10.118 (CW), 10.130 (digital) | CW / FT8 | WARC band — no contests; often quiet |
| 20 m | 14.032 (CW), 14.285 (SSB) | CW / SSB | International DX; essential for S2S contacts |
| 17 m | 18.092 (CW), 18.130 (SSB) | CW / SSB | WARC band; useful DX path when 20m crowded |
Alert in advance: post your planned activation to SOTAwatch3 (sotawatch.sota.org.uk) at least 30 minutes before arriving on the summit. Chasers monitor upcoming alerts and will be ready when you call. An alerted activation typically generates a pile-up within the first 60 seconds of calling CQ SOTA — unalerted activations may require many CQ calls to generate any response.
How many contacts do I need to activate a summit?
SOTA rules require a minimum of 4 QSOs with different stations to qualify a summit activation. At least one QSO must be on a recognised SOTA band. The 4-contact minimum is easily achieved on any of the four bands covered by this antenna during normal propagation — a typical activation generates 20–80 QSOs over 30–90 minutes of operating.
Can I use this antenna with a QRP transceiver?
Yes — the linked vertical is specifically designed for QRP SOTA operation. The most popular SOTA combinations are this type of antenna with the Elecraft KX2, KX3, Yaesu FT-818, or one of the many QRP kit radios (Xiegu G90, mcHF, or Minion SDR). At 5–10 W into a well-set-up vertical on a summit, 40 m pile-ups of 20–30 stations are routine during good conditions.
Do I need an ATU for this antenna?
With the element lengths given above, SWR should be below 1.5:1 on each band without an ATU — many QRP radios tolerate this without complaint. An ATU (the LDG Z-11 Pro or the built-in tuner in a KX3) allows fine-tuning to SWR 1.0:1 and can compensate for rain detuning. A small manual ATU (QRP Tuner or homebrew L-network in a tin) adds 80–120 g to pack weight — worthwhile if the radio lacks a built-in tuner.
What fishing pole mast is best for SOTA?
The 7 m fibreglass telescopic fishing poles sold for approximately £15–25 on eBay or Amazon under brands like "Spro", "Shakespeare", or generic Chinese fishing pole are the standard. Look for a fully extended length of 6.8–7.2 m and a collapsed length of 55–65 cm. Avoid carbon-fibre poles — they are conductive and will short your antenna. Fibreglass is essential. Weight should be 250–350 g for a quality 7 m pole.
Can I include 80m in the linked vertical?
Yes — add a fifth section below the 40 m link for 80 m: 80 m λ/4 ≈ 20.4 m total element, so the 80 m section adds 20.4 − 10.07 = 10.33 m below the 40 m link. This needs a longer mast (a second telescopic pole attached below the first, or use the 80 m section as an inverted-L with 10.07 m vertical and 10.33 m horizontal). The radials also need to match: 20.4 m long for 80 m. Many SOTA operators find 40 m sufficient for most activations and keep the system lighter by omitting 80 m.
Is a vertical better than a dipole for SOTA?
Both work well. The vertical requires only one mast and provides omnidirectional coverage — essential when you do not know which direction chasers are. The horizontal dipole requires two supports (poles or natural anchors) but gives slightly higher gain in the broadside direction and lower ground-wave noise. On a hilltop with clear ground slope, the vertical often out-performs the equivalent dipole at low elevation angles because the elevated ground plane extends the vertical's effective aperture. Many SOTA operators carry both and choose based on the summit's terrain.