Build a Portable Linked Dipole Antenna
The linked dipole is the most practical multi-band HF antenna for portable operation — a center-fed wire dipole with removable link connectors at calculated positions along each leg that allow the effective electrical length to be changed band-by-band by clipping or unclipping sections of wire. No tuner required. No traps to fail. No complex phasing networks. Simply walk out to the end of the antenna, disconnect the links for the shorter band, and operate. The linked dipole is the go-to antenna for SOTA activators, POTA operators, and any ham who wants efficient resonant operation on 40m, 20m, 15m, and 10m from a single lightweight antenna that packs to a 200g bundle in a daypack.
The Link Concept
A dipole is resonant on one frequency — the frequency at which its total length equals a half-wavelength. The linked dipole extends this to multiple frequencies by making the element length adjustable through removable wire links:
Link Connector Design
The link connectors at each band-change position must be quick to disconnect in the field, electrically reliable, and lightweight. Several options exist:
Wire Selection for Portable HF
Wire weight is the critical parameter for a SOTA/POTA antenna — heavy wire is unacceptable for a summit pack-in. The linked dipole uses ultra-lightweight stranded wire throughout:
Linked Dipole vs Other Portable HF Antennas
The linked dipole competes with several other portable HF antenna designs that are popular in SOTA/POTA communities:
- vs EFHW (end-fed half-wave): the EFHW feeds from one end with a transformer, is easy to string in the field, and covers multiple bands if the length is chosen carefully. The linked dipole requires no transformer but needs a center feedpoint elevated. For tree-sparse terrain, the EFHW's single-point hang is an advantage. For balanced, symmetric performance, the linked dipole wins.
- vs trapped dipole: a trapped dipole adds resonating LC circuits at each band transition, allowing all bands to be covered without physically changing links. The trade-off: traps add weight, reduce efficiency (trap losses), and can fail. The linked dipole has no lossy traps and full wire efficiency on every band.
- vs random wire with tuner: a random wire with an ATU is the simplest field antenna to string but the tuner adds weight and the random wire has variable efficiency depending on frequency. The linked dipole is resonant on each band — no tuner needed, maximum efficiency every time.
- Best case for linked dipole: SOTA summits and POTA parks with trees for end support, where a field-resonant antenna without a tuner is prioritized for low power (QRP) operation where tuner losses matter most.
| Band | Freq (MHz) | Each leg length | Total dipole | Link position (from center) | Section added by links |
|---|---|---|---|---|---|
| 10m | 28.300 | 8.3 ft (2.53 m) | 16.6 ft | 8.3 ft from center | — (tip section, always present) |
| 15m | 21.100 | 11.0 ft (3.35 m) | 22.0 ft | 11.0 ft from center | 2.7 ft (0.82 m) added per leg for 15m |
| 20m | 14.100 | 16.5 ft (5.03 m) | 33.0 ft | 16.5 ft from center | 5.5 ft (1.68 m) added per leg for 20m |
| 40m | 7.100 | 33.4 ft (10.18 m) | 66.8 ft | 33.4 ft from center | 16.9 ft (5.15 m) added per leg for 40m |
Portable Linked Dipole Calculator
| Section | Length each leg | Between which links | Label color |
|---|---|---|---|
| Section A — 10m tip | 8.3 ft (100 in / 2530 mm) | From feedpoint to 10m/15m link | Red |
| Section B — 15m extension | 2.7 ft (32.4 in / 823 mm) | From 10m/15m link to 15m/20m link | Yellow |
| Section C — 20m extension | 5.5 ft (66 in / 1676 mm) | From 15m/20m link to 20m/40m link | Green |
| Section D — 40m extension | 16.9 ft (202.8 in / 5151 mm) | From 20m/40m link to end of antenna | Blue |
Materials for a 40/20/15/10m linked dipole with Anderson Powerpole links
Why a Balun Is Essential on All Bands
The linked dipole is a balanced antenna — each arm carries equal and opposite current. The coaxial feedline is unbalanced. Without a balun, common-mode current flows on the coax outer braid, effectively making the feedline part of the antenna. This distorts the radiation pattern, introduces RF into the shack, and changes the feedpoint impedance on every band:
Feedpoint Enclosure Assembly
The feedpoint enclosure houses the balun, SO-239 connector, and the wire connection points for the two dipole legs. It hangs from the center support cord in the field:
Building the 4-Band Linked Dipole
Build both legs simultaneously — cut and terminate all sections before assembling the full legs. Label every section and every connector pair clearly before putting anything in the kit bag. A mislabeled or mixed-up connector is the most common field error with a linked dipole, and it is far easier to fix in the workshop than on a summit.
Cut All Wire Sections — Both Legs
Cut eight wire sections in total — four per leg (Section A through D) — from the #24 AWG wire roll. Cut each section 3 inches longer than the table dimension to allow for connector termination. Label every section immediately with a small piece of coloured electrical tape matching the colour code in the table:
Terminate All Wire Sections with Powerpole Connectors
Each wire section end that connects to another section gets an Anderson Powerpole connector. The feedpoint ends of the A sections (which connect to the feedpoint, not to another section) get solder lugs instead of Powerpoles:
Build the Feedpoint Balun Assembly
Wind the 1:1 current balun on the FT-240-31 toroid and assemble the feedpoint enclosure:
Assemble Complete Legs and Label Link Positions
Connect all sections of each leg together (all Powerpole links mated) to verify the complete 40m dipole assembly, then mark each link connector pair with a small cable tie tag identifying its band:
Field Deployment and Initial Tuning
Deploy the dipole in inverted-V configuration (center elevated, ends near ground) for the initial tuning — the most common SOTA/POTA deployment style. A single support point at the apex keeps the feedpoint at useful height without requiring two tall trees:
Verify All Four Bands and Document Final Lengths
After tuning all four bands, verify the SWR on each band with the antenna in its final deployed position. Take all measurements with the NanoVNA at the feedpoint (not at the shack end of the coax) for accurate results:
Changing Bands in the Field
The linked dipole's only operational requirement is walking to the link connectors when changing bands. The procedure is quick once practiced:
Deployment Configurations
The linked dipole can be deployed in several configurations depending on available terrain and supports:
- Inverted-V (most common): center elevated to maximum possible height, ends near ground at 30–45° slope. Requires only one tall support. Radiation pattern is omnidirectional — good for working pile-ups from multiple directions on SOTA/POTA.
- Flat-top dipole: both ends and center at similar heights, antenna horizontal. Requires two equal-height supports separated by 66 feet (for 40m) — possible with two tall trees but requires more site selection time. Better low-angle DX radiation than inverted-V.
- Sloper: one end high, other end near ground, feedpoint somewhere between. Quick deployment with one support point and no horizontal end guy. Radiation is directional — good for targeting a specific geographic area from a summit.
- NVIS (Near-Vertical Incidence Skywave): center elevated only 10–20 feet, very low wire — produces near-vertical radiation for regional contacts within 300 miles. Useful for activating from a summit where regional contacts (state QSOs for POTA credit, nearby chasers for SOTA) are the goal rather than DX.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| High SWR on all bands after correct tuning in original session | Link connector not fully seated — common in cold or wet weather | Physically check every link connector — press firmly until click heard | Re-mate all link connectors fully; apply light grease to Powerpole contacts for cold-weather operation |
| SWR minimum at correct frequency but above 2.5:1 | Feedpoint balun not working — common-mode current on coax | Move feedline while watching SWR — if it changes, choke is inadequate | Rewind balun with more turns (10 turns minimum); or add 5 type-31 ferrite beads to coax at feedpoint |
| One band has correct SWR but adjacent bands shifted | Wrong section disconnected — link confusion in the field | Verify which links are connected vs disconnected; count from feedpoint out to each link position | Reconnect all links (40m config); verify correct config for target band per the band change procedure |
| SWR minimum 500+ kHz below target on a specific band | Wire section too long for that band's link position | Measure section length from feedpoint to the relevant link — compare to table | Trim the relevant section (A for 10m, B for 15m, C for 20m, D for 40m) in 3-inch increments; re-measure |
| SWR varies dramatically as wind moves the antenna | Normal behavior — moving antenna near ground affects impedance; or near-tree coupling | Deploy ends higher or pull them taut to reduce movement | Tension the end guy lines more firmly; add small weights to element tips to damp movement |
| Link connector lost in the field | Disconnected section not stored in bag — fell in brush | Check ground near where the link was disconnected | For the field emergency: twist the wire ends together tightly as a temporary splice; re-connect properly at home |
Can I add 80m to this antenna?
Yes — add a fifth section per leg (Section E) extending from the 40m link position outward to a total leg length of 66.5 feet. The 80m extension per leg would be 66.5 − 33.4 = 33.1 feet of additional wire per leg, connected via a fourth Powerpole link pair. An 80m linked dipole is 133 feet total — a substantial antenna for a summit, but manageable at many SOTA and POTA sites with long open terrain. The 80m leg tips can droop significantly (near-NVIS configuration) if the terrain does not permit full horizontal deployment. An 80m linked dipole covering 80/40/20/15/10m is the most popular configuration for operators who want maximum band coverage from a single portable antenna.
Do I need a tuner with a linked dipole?
No — this is the linked dipole's primary advantage over other portable multi-band antennas. Each band configuration produces a resonant half-wave dipole with a feedpoint impedance of approximately 70–75 Ω. With the 1:1 current balun at the feedpoint, the SWR on 50 Ω coax is approximately 1.4:1 — well within the range of every HF radio's built-in ATU and within QRP radios' typical no-tuner operating tolerance. Most SOTA operators run 5–10W from a KX2, KX3, or similar radio directly to the linked dipole without any ATU. This eliminates the tuner's weight and loss — meaningful for a 5W QRP station where every fraction of a watt counts.
How high does the feedpoint need to be for effective HF operation?
For the inverted-V configuration, the feedpoint height determines the radiation angle and the practical efficiency of the antenna. As a rough guide: at 30 feet (approximately λ/4 on 20m) the main radiation lobe on 20m is at approximately 40° elevation — good for skip distances of 500–1500 miles, covering the bulk of POTA and SOTA chase contacts. At 50 feet the lobe drops to 25° — better for longer DX. At 15 feet (barely off the ground) the antenna is essentially NVIS and works best for regional contacts under 300 miles. For typical SOTA summits where the nearest suitable tree branch is at 20–30 feet, the linked dipole in inverted-V configuration is highly effective for typical activation distances and is competitive with far more complex portable station setups.
What is the difference between inverted-V and flat-top dipole in practice?
A flat-top dipole at the same feedpoint height as an inverted-V performs better for low-angle DX because the ends of the dipole are at full height — the current distribution extends up to the highest point. An inverted-V has its ends at ground level where radiation efficiency is lower, and the end capacitance changes the effective electrical length slightly. In practice for SOTA/POTA contacts at distances under 3000 miles, the difference between inverted-V and flat-top is not operationally significant — both produce effective contacts. The inverted-V wins on practicality: it requires only one tall support instead of two, deploys faster, and works in terrain where two suitable trees far apart are unavailable. For a dedicated DX-focused portable station at a base camp with good tree options, the flat-top is worth the extra deployment effort.
How do I know which links to disconnect for each band?
A simple rule: to go to a higher frequency (shorter band), disconnect from the outermost link inward until you reach the correct band's position. To go to a lower frequency (longer band), reconnect links from the inner position outward. Mnemonic: "short bands, short wire — disconnect from outside." For field use, some operators attach a laminated reference card to the feedpoint enclosure showing which link positions are connected for each band: 40m = all connected; 20m = leave D disconnected; 15m = leave C and D disconnected; 10m = leave B, C, and D disconnected. After the first few band changes in the field, this becomes intuitive and the reference card becomes unnecessary.
Can I use this antenna indoors or in a restricted HOA environment?
The linked dipole in its 10m configuration (16.6 feet total) can fit in a large backyard or between a house and a fence. In its 20m configuration (33 feet total) it fits diagonally across many suburban lots when deployed as an inverted-V from a fishing pole support. For HOA-restricted environments, the 10m or 15m configuration deployed in an attic is possible — attic installation provides some RF shielding from neighbors' noise and produces effective regional contacts even at low heights. For a 40m indoor or attic antenna at 66 feet total, a suitably large property or attic space is needed. The linked dipole's ability to function on shorter configurations makes it more adaptable to restricted spaces than a full 40m dipole that demands the full 66-foot span regardless of how it is configured.