Build a Linked Dipole for SOTA and POTA
The linked dipole is the most versatile portable HF antenna in amateur radio — a multi-band resonant dipole whose elements are divided into switchable sections by quick-connect links, allowing the operator to change bands by walking to each end and connecting or disconnecting wire segments in seconds. No ATU, no complicated matching network, no loading coils — just a direct 50 Ω feed on each band from a single feedpoint. A five-band linked dipole covering 40m, 20m, 17m, 15m, and 10m fits in a stuff sack the size of a water bottle and weighs under 12 ounces including feedpoint, connectors, and winding card. It is the standard antenna for SOTA (Summits On The Air) activators worldwide and works equally well for POTA (Parks On The Air), portable QRP operation, and emergency deployment. This guide covers linked dipole theory, complete wire length calculations, link connector options, feedpoint construction, winding for transport, deployment techniques with a mast or trees, and field operating tips.
The Linked Dipole Concept
A resonant half-wave dipole for any HF band presents approximately 70 Ω at its feedpoint — close enough to 50 Ω coax for direct feeding with SWR under 1.5:1 without any matching network. The linked dipole exploits this by building a single dipole that can be resonant on multiple bands through switchable wire sections:
Wire Selection — Weight vs Performance
Wire selection for a portable HF dipole involves a trade-off between weight, strength, and RF performance. At HF frequencies the conductor loss of thin wire is negligible — the choice is driven entirely by mechanical considerations:
Link Connector Options
The link connectors at each band junction are the most important component for field reliability. They must connect and disconnect quickly with gloves on, stay connected during use, and not corrode after years of outdoor use:
- Banana plugs and sockets (most popular): 4mm banana plugs inline in the wire are the standard SOTA linked dipole connector. They snap together with a satisfying click, can be connected in seconds, are inexpensive, and are small enough to be barely noticeable in the wire. Use gold-plated or nickel-plated versions rated for outdoor use. Bare brass corrodes in salt air environments — nickel plate is preferred for coastal operations.
- Anderson PowerPoles: the 15A red/black PowerPole connector used throughout amateur radio emergency communications. Weather-resistant, locking, and finger-friendly with gloves. Slightly larger than banana plugs but extremely reliable. Some operators use these exclusively for their rugged locking action.
- Bullet connectors (2mm or 3.5mm audio): small gold-plated bullet connectors from the RC hobby market. Extremely small and light — the least obtrusive link option. Slightly harder to connect with cold or gloved fingers than banana plugs.
- Soldered wire loops: the simplest and lightest approach — no commercial connector at all. Each link point is a small loop of wire that is connected by threading the adjacent wire through and twisting. More resistant to accidental disconnection than any connector, but slower to change bands. Used by ultralight SOTA operators who rarely change bands during an activation.
Linked Dipole vs EFHW vs Other Portable Antennas
The linked dipole competes with several other portable HF antenna designs for SOTA and POTA use:
- vs EFHW (end-fed half-wave): the EFHW requires only one support point (vs two for a dipole) and covers multiple bands without relinking. However, it requires a 49:1 matching transformer and is more sensitive to installation geometry. The linked dipole is simpler, cheaper, and more predictable — especially for new portable operators. See the EFHW SOTA/POTA guide for that design.
- vs trap dipole: a trap dipole covers multiple bands without link connectors but uses lossy inductors at each band boundary. The linked dipole has no inherent loss — it outperforms a trap dipole on every band it covers. The only advantage of traps is one-touch band changing without walking to the ends.
- vs fan dipole: a fan dipole uses separate dipole elements for each band all connected at the feedpoint — no reconnection needed but requires more support points and tangles badly in wind. The linked dipole is mechanically simpler and stores much more compactly.
- vs commercial SOTA antennas (LNR EF-10/20/40, SOTAbeams Band Hopper): commercial designs are well-engineered but cost $80–150. A homebrew linked dipole performs identically for $15–20. The main advantage of commercial versions is tested dimensions and a tidy finish — neither of which is hard to achieve with careful construction.
| Band | Design freq (MHz) | Total half-wave (each leg) | Cumulative leg length | Segment added at this link | Notes |
|---|---|---|---|---|---|
| 10m | 28.500 | 8.18 ft (2.49 m) | 8.18 ft | 8.18 ft (innermost segment) | Connected from feedpoint; all outer links open |
| 15m | 21.200 | 11.00 ft (3.35 m) | 11.00 ft | 2.82 ft (0.86 m) added at Link 1 | 10m segment + this addition = 15m resonance |
| 17m | 18.100 | 12.89 ft (3.93 m) | 12.89 ft | 1.89 ft (0.58 m) added at Link 2 | 10m + 15m add + this = 17m resonance |
| 20m | 14.175 | 16.46 ft (5.02 m) | 16.46 ft | 3.57 ft (1.09 m) added at Link 3 | Cumulative inner three segments + this |
| 40m | 7.100 | 32.89 ft (10.03 m) | 32.89 ft | 16.43 ft (5.01 m) added at Link 4 | Full dipole leg length; outermost segment |
Linked Dipole Sota Pota Calculator
All dimensions are per leg — each dipole has two legs of equal length. Cut each segment 3–4% longer than shown and trim to resonance with a NanoVNA in the field. Design frequencies are band centre; for CW/FT8 operation, tune for the lower segment of each band. Total wire required per leg: approximately 33 ft; total for complete dipole: 66 ft plus feedpoint connections.
Materials for a 5-band linked dipole covering 40m, 20m, 17m, 15m, and 10m
Building the 5-Band Linked Dipole
Build sequence: construct feedpoint → cut all segments slightly long → solder link connectors → deploy in inverted-V configuration → trim each band segment to resonance with NanoVNA → document final lengths → wind on storage card. The trimming procedure in the field is the most important step — build with generous extra length and trim rather than cutting to the calculated dimensions and hoping they are correct.
Build the Feedpoint Centre Insulator
The feedpoint is the structural and electrical heart of the linked dipole. It must support the mast attachment, the two wire legs, and the coax connection, all while remaining light and weatherproof. Commercial SOTA feedpoints from SOTAbeams or Packtenna are polished and worth buying if available. For a homebrew feedpoint, use a 4-inch × 2-inch piece of 1/4-inch acrylic or fibreglass plate:
Cut All Wire Segments — Long, to Be Trimmed
Cut each wire segment 5% longer than the table values. The extra length is removed during field trimming. Cutting short is irreversible; cutting long and trimming is the correct approach for wire antennas. For each leg, cut five segments:
Solder Link Connectors to Each Segment
Solder banana plug connectors to the end of each segment and banana socket connectors to the start of the next segment. Work through all ten segments (five per leg), being careful to maintain the correct polarity — the plug at the inner end connects to the socket at the outer start of the next segment:
Deploy and Trim Each Band — Field Resonance Tuning
Deploy the dipole in an inverted-V configuration — feedpoint at the mast top (6–7m high), the two legs sloping down to ground anchors or tree branches at 30–45° slope angle. Connect all segments for 40m. Connect the NanoVNA to the feedpoint via a short coax jumper. Trim and tune each band starting from the innermost (shortest) band and working outward:
Wind onto Storage Card and Pack for Field Use
Proper storage prevents tangles in the field — the most frustrating problem with wire antennas. The goal is a winding system that allows the antenna to be deployed and packed in under 5 minutes:
Inverted-V vs Flat Dipole Deployment
The linked dipole can be deployed in several configurations depending on available supports. Each has practical advantages:
- Inverted-V (most common for SOTA): feedpoint at the mast top, both legs sloping down to ground anchors at approximately 30–45° from vertical. Requires only one support (the mast) and fits in a compact footprint — important on narrow summit ridges. The inverted-V pattern has slightly more high-angle radiation than a flat dipole at the same apex height, which is actually beneficial for SOTA NVIS contacts on 40m and 80m.
- Sloper: feedpoint at the mast top, one leg horizontal and the other sloping steeply down. Fits in a smaller footprint than an inverted-V. Pattern is asymmetric — more radiation in the direction of the sloped leg. Useful when summits have a cliff or obstruction on one side.
- Flat horizontal (best for DX): feedpoint at a tree or mast, both legs horizontal at the same height. Requires two support points of equal height — two tall trees or a mast and a tree. Provides the lowest radiation angle of the three configurations and the best DX performance on 20m, 17m, 15m, and 10m. For POTA operations in parks with tall trees, a flat dipole at 10m height is outstanding.
- End supports: tie a length of paracord to each end insulator, throw it over a tree branch, and tie off at the base. The dipole ends hang at 5–8m in trees without requiring a separate mast for the ends — the centre mast supports the feedpoint and the tree branches support the ends. This configuration requires no end pegs and deploys very quickly in wooded parks.
SOTA and POTA Operating Tips
The linked dipole antenna is one part of the SOTA/POTA equation — effective field operating maximises the contacts per activation:
- Self-spotting: post your activation on the SOTA Spotter (sota.watch) or POTA Spots (pota.app) before or as soon as you begin operating. Chasers monitoring these sites will immediately QSY to your frequency and call you — contact rate often jumps from zero to several per minute within seconds of spotting.
- CW vs SSB: CW contacts typically require 6–10 dB less power to complete than SSB — this means 5W CW reaches stations that 50W SSB might struggle to work from a challenging summit site. If FT8 is available on your radio (IC-705, FT-818 with computer), it is even more efficient than CW for weak paths. Many SOTA activators use all three modes during an activation.
- 40m first, then higher bands: on most SOTA and POTA activations, 40m provides the most reliable regional contacts (500–1000 km) during daytime. 20m provides DX contacts especially from elevated summits. 17m and 15m are excellent for DX when the bands are open. 10m is intermittent but spectacular during solar maximum.
- Band change procedure: to change bands, shout or transmit that you are changing bands, then walk to each end of the dipole and connect or disconnect the appropriate link. A NanoVNA spot-check after reconnecting takes 30 seconds and confirms the band change was successful before resuming operation.
- Doppler spotting on FT8: if using FT8 (WSJT-X), activating on the standard FT8 frequencies (14.074 MHz, 7.074 MHz, 21.074 MHz) allows the POTA network's automated reverse beacon network to spot you automatically without manual self-spotting.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| SWR high on one band, others fine | Link connector for that band not fully engaged; or cold solder joint opened | Walk to each link on the affected band; firmly press banana plugs together; feel for a click; visually inspect connections | Reconnect links firmly; if a connector fails, bypass it with a short wire twisted around both conductors as an emergency field fix |
| SWR high on all bands simultaneously | Open circuit at feedpoint — SO-239 connection failed, or choke balun connection loose | Check feedpoint connections; measure resistance between SO-239 centre pin and one dipole leg terminal | Re-solder feedpoint connections; check choke balun connections; verify coax connector is seated fully in SO-239 |
| RF feedback in radio audio — RF in shack | Inadequate common-mode choke; coax acting as antenna | Touch the coax body — if you feel slight warmth or RF tingle, common-mode current is present | Add more ferrite choke turns at feedpoint; ensure coax exits feedpoint at 90° to dipole axis for at least 10 ft |
| Resonant frequency shifted from field-tuned values | Different deployment height or geometry vs when tuned; wet wire changes velocity factor | Quick NanoVNA spot-check at current deployment height | Accept within 2:1 SWR — most QRP radios tolerate this; or trim a small amount from the affected segment if consistently off |
| Wire tangle during deployment | Wire not wound properly on storage card; segments crossed during packing | Lay out full antenna on grass and sort before deployment | Deploy methodically — walk one leg at a time from the feedpoint outward; never throw a balled-up wire from the feedpoint end |
| Mast keeps falling — instability on summit | Guy lines inadequate; wind or soft ground not holding pegs | Is the mast guyed at at least 3 points? Are pegs fully seated in solid ground? | Add a fourth guy line; use rock anchors (cord looped around a heavy rock) instead of pegs on hard rocky summits; lengthen guys to widen the guying base |
Do I need an ATU with a linked dipole?
No — that is the principal advantage of the linked dipole. Each band uses a resonant wire length that presents approximately 50–70 Ω at the feedpoint, directly matched to 50 Ω coax with SWR under 1.5:1. Most modern QRP radios are happy driving a 1.5:1 SWR load without any matching network. The only exception is if the antenna is deployed at very low height (under 0.1λ above ground) on lower bands, where the feedpoint impedance can drop below 25 Ω. For field deployment at typical heights, no ATU is needed.
How many contacts can I expect from a SOTA activation with 5W?
On a typical SOTA activation with 5W SSB, a self-spotted activation on a clear day yields 10–30 contacts in 30–60 minutes, depending on band conditions, your location, and how many chasers are active. 5W CW or FT8 in the same conditions typically produces more contacts because the modes are more efficient. From a prominent summit with a clear take-off in all directions, 50+ contacts in a single activation is achievable with a good linked dipole and favourable conditions. From a challenging summit surrounded by higher terrain, 4 contacts (the SOTA qualifying minimum) may take the full activation window on 40m.
Can I add 80m to the linked dipole?
Yes — add a fifth link and a pair of segments approximately 32 ft long (the additional length needed beyond the 40m tips to reach 80m resonance at 3.700 MHz). The 80m addition makes the full dipole approximately 65 ft per leg — which requires enough deployment space. On most SOTA summits, 65 ft per leg is achievable by running the legs along the ridgeline. The 80m segment is extremely useful for early-morning and evening NVIS contacts during activations, when 40m is dead and 80m provides reliable regional coverage.
How do I choose which band to operate on from a summit?
A quick check on the DX cluster or the WSPR map on pskreporter.info shows which bands are active from your summit location before you deploy. As a general guide: 40m is reliable for regional contacts (within 1,000 km) most of the time; 20m opens for DX contacts from mid-morning to mid-afternoon; 17m and 15m track solar activity — both are excellent during solar maximum and unreliable during solar minimum; 10m is spectacular during solar maximum (intercontinental QRP contacts are routine) but nearly dead at solar minimum. For a first SOTA activation, 40m in the morning and 20m in the afternoon is the reliable strategy.
What is the minimum height for the feedpoint?
For the 40m band, the feedpoint should be at least 5–6 metres (16–20 ft) above ground for acceptable performance. Below 4 metres, the ground proximity significantly loads the lower HF bands, dropping the feedpoint impedance and increasing SWR. For the upper bands (17m, 15m, 10m), a feedpoint at 4 metres is perfectly adequate. A 7-metre SOTA mast provides a useful compromise — high enough for good 40m performance but light and portable enough for summit carry. A 10-metre mast provides noticeably better 40m performance but weighs significantly more.
Can I use the linked dipole for portable QRP from home?
Absolutely — the linked dipole is not only a summit antenna. Many operators deploy it in their backyard, at a campsite, from a hotel room window sill, or from a beach. Anywhere you can erect a 7-metre mast or find two trees 70 ft apart, the linked dipole works as well as any HF antenna. For apartment operators who want to operate HF legally and effectively during visits to suitable locations, a linked dipole that travels in a coat pocket is often the most practical HF antenna available.