Linked Dipole Tips

The Linked Dipole

A linked dipole is a multiband HF antenna that's basically a dipole with switchable electrical lengths. Instead of using traps or a tuner, you physically change the length of the antenna by connecting or disconnecting wire "links." Each configuration resonates on a different band.

Think of it as: one dipole, multiple personalities

What It Is (Conceptually)

  • A normal dipole is resonant on one band because its length is fixed.
  • A linked dipole has extra wire sections added to each leg.
  • Those sections are connected via links (breaks in the wire you can open or close).
  • When you close a link, you add wire → antenna gets longer → lower frequency band.
  • When you open a link, you remove wire → antenna gets shorter → higher frequency band.

Example:

  • Links open → tuned for 20 m
  • Close first set of links → tuned for 40 m
  • Close another set → tuned for 80 m

No traps, no lossy components, very efficient.

Why People Like Them

Pros

  • Very efficient (no traps, low loss)
  • Simple, cheap, and robust
  • Easy to understand and troubleshoot
  • Works great with low power (QRP) or full legal limit

Cons

  • You must physically change bands (go outside or lower the antenna)
  • Not instant band hopping
  • Can get a bit "wire spaghetti" if you add lots of bands

Basic Construction

1. Choose Your Bands

Common combos:

  • 40 / 20
  • 80 / 40 / 20
  • 40 / 30 / 20 / 17

Tip: adjacent bands are easier to manage.

2. Cut for the Lowest Band First

Start with a half-wave dipole for your lowest frequency.

Rule of thumb:

Total length (feet) ≈ 468 / frequency (MHz)

Then split it evenly between the two legs.

Example (40 m at 7.1 MHz):

  • Total ≈ 66 ft
  • Each leg ≈ 33 ft

3. Add Links for Higher Bands

  • Cut the antenna long
  • Insert breaks where you want band changes
  • Add wire beyond each break for the lower band

Each leg will look like:

Feedpoint ─── wire ── link ── extra wire ── link ── more wire

The shortest section (closest to the feedpoint) is for the highest band.

4. Making the Links

Popular methods:

  • Anderson Powerpoles
  • Bullet connectors
  • Small banana plugs
  • Wire loops + carabiners
  • Ring terminals + wing nuts

Build hints:

  • Make them weatherproof
  • Ensure good electrical contact
  • Leave a little slack so tension isn't on the connector

5. Tuning Order (Important!)

Always tune from highest band to lowest:

  1. Open all links → tune highest band
  2. Close first set → tune next band
  3. Close next → tune lowest band

If you tune low band first, you'll mess up everything above it.

Installation Tips

Works best as:

  • Flat-top dipole
  • Inverted-V (very popular)
  • Height matters more than perfection
  • Use a good choke/balun (1:1 current balun) at the feedpoint, it will work without one though
  • Label your links (future-you will thank you)

When a Linked Dipole Is a Great Choice

  • Portable / WWBOTA / SOTA / POTA ops
  • Simple home HF setup
  • QRP rigs
  • Anyone who values efficiency over convenience

M0ICR LINKED DIPOLE CALCULATOR

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EFHW Antenna Guide

What is an EFHW Antenna?

An EFHW (End-Fed Half-Wave) antenna is a half-wave wire antenna fed at one end. Because the feedpoint impedance of a half-wave at the end is very high (typically 2–4 kΩ), an impedance transformer (unun) is used to match the antenna to 50 Ω coax.

EFHW antennas use:

  • A single long wire
  • One main support (sometimes two)
  • No tuner when properly cut

Why Use an EFHW?

Advantages

  • Very simple physical layout
  • Easy to deploy in limited space
  • Excellent for portable or stealth installs
  • Multiband operation via harmonics
  • No traps or coils in the radiator

Disadvantages

  • Requires a transformer (unun)
  • Higher common-mode current than a dipole
  • High RF voltage at feedpoint
  • Grounding and choking are important

How Does Multiband Operation Work?

A half-wave antenna is also resonant at harmonic frequencies.

Examples:

  • 40 m EFHW → 20 m, 15 m, 10 m
  • 80 m EFHW → 40 m, 20 m, 15 m, 10 m

Non-harmonic bands usually require a tuner.

EFHW Cut Chart (Metric Primary)

Cut long, then trim.

Lowest Band Length (m) Length (ft)
10 m ~5.0 m ~16.4 ft
20 m ~10.1 m ~33.1 ft
40 m ~20.1 m ~66 ft
80 m ~40.2 m ~132 ft

Notes

  • Insulated wire usually needs slight shortening
  • Height and nearby objects affect resonance
  • Always trim from the far end

Impedance Transformer (49:1 Unun)

Why 49:1?

A half-wave end feed impedance is typically 2500–3000 Ω. A 49:1 transformer matches this well to 50 Ω.

Typical 49:1 Unun Build

Core

  • FT-240-43 (most common)
  • FT-240-52 (also suitable)

Turns

  • Primary: 2 turns
  • Secondary: 14 turns
  • Turns ratio: 7:1 → impedance ratio ≈ 49:1

Wire

  • Enamelled copper or PTFE insulated wire
  • Keep leads short and neat

Enclosure

  • Weatherproof box
  • SO-239 or N-type connector
  • High-voltage output stud

⚠️ Feedpoint voltage can be very high — spacing and insulation matter.

Counterpoise and Choking

Counterpoise Options

  • Short wire: 1–3 m (3–10 ft)
  • Coax shield acting as return
  • Ground rod (fixed stations)

Choke Recommendation

  • 1:1 common-mode choke
  • At feedpoint or 1–3 m (3–10 ft) down coax
  • Ferrite beads or toroid choke preferred

Good choking = less RF in the shack.

Installation Options

Common EFHW layouts:

  • Sloper
  • Inverted-L
  • Horizontal
  • Random-angle (portable friendly)

Tips

  • Get the wire as high as possible
  • Keep feedpoint accessible but out of reach
  • Keep wire ends away from metal
  • Never touch antenna while transmitting

Tuning Procedure

  1. Start with the lowest band
  2. Measure SWR at target frequency
  3. Trim 2–5 cm (1–2 in) at a time
  4. Re-check all bands after each trim

Never trim at the feedpoint.

Power Handling

  • High RF voltage at feedpoint
  • Use adequate spacing and insulation
  • Ensure transformer is rated for power level
  • 100 W is common; higher power requires careful design

M0ICR END FED HALF WAVE (EFHW) CALCULATOR

Select Primary Band

T2LT / Vertical Coax Antenna Guide

1. Overview and History

The T2LT antenna, sometimes called a "Vertical Coax" or "Coaxial Vertical," is a type of HF vertical antenna that uses coaxial cable sections as part of its radiating element.

  • Origin: 1960s–70s amateur experimentation
  • Design idea: Uses the coax braid as a radiator
  • Use: HF where horizontal space is limited

Key feature: Vertical polarisation → good for DX.

2. Use on HF

  • 80/40m require long coax and counterpoise
  • 20/15/10m are easier and common
  • Often used with a tuner

3. Construction Methods

  1. Coaxial cable (RG-58 / RG-8)
  2. Support mast or PVC
  3. Insulators
  4. Balun or matching network
  5. Radials / counterpoise

4. Advantages

  • Compact footprint
  • Good DX performance
  • Weather resistant

5. Disadvantages

  • Can be lossy if poorly built
  • Vertical polarisation only
  • Needs careful tuning

6. Summary

Feature Notes
Frequency80–10m (design dependent)
PolarisationVertical
SpaceLow horizontal
EfficiencyGood with radials

VERTICAL HALF-WAVE DIPOLE (T2LT)

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