HF Collinear Antenna that gives gain approaching that of a 2 element Yagi, but in two directions

VIDEO

If a full-size HF Yagi is out of the question — no tower, limited budget, or restrictive garden — a three-element horizontal collinear is an attractive compromise. It can deliver nearly the gain of a two-element Yagi while radiating in two opposite directions (broadside). It is a relatively simple wire build and is particularly useful on 20 metres where the design works best.

A three-element collinear for HF is a single horizontal wire split into three radiating sections. Between those sections sit two phasing stubs (quarter-wave sections) that delay the current so all three radiating sections are in phase. The result is a narrower broadside beam and roughly just under 3 dB of gain in each of the two opposite directions.

• A typical two-element Yagi (driven element plus reflector) can produce around 3.5–4 dB forward gain versus a dipole. It also provides front-to-back rejection that a collinear does not.
• However, much of the perceived extra signal from a tower-mounted Yagi comes from height above ground. Raising a horizontal radiator reduces the takeoff angle and improves DX performance, so users often hear more benefit than the raw dB figures imply.
• The three-element collinear gives a similar increase in signal strength to a two-element Yagi but in two directions (north and south, for example), making it useful if you want gain toward two different continents without a rotator or tower.

How the phasing stubs work

The two phasing sections are quarter-wave stubs, shorted at the far ends. Each stub provides a 180° phase shift so that the three radiating sections operate in phase. These stubs can be made from 450 Ω ladder line or coaxial cable (as shorted quarter-wave lines). If you use coax, the physical stub length is reduced by the coax velocity factor.

Stubs do not have to hang straight down. You can loosely coil them (a diameter of 150–200 mm or a few inches) to keep them tidy and less visually obtrusive. Do not coil tightly — keep the turns loose to avoid unwanted coupling or changing the electrical length too much.

Use the standard wavelength formulas to size the radiating sections and the stubs:

• Half-wave (λ/2) in metres = 150 / f(MHz)
• Quarter-wave (λ/4) in metres = 75 / f(MHz)
• If using coax for the stub, multiply the quarter-wave length by the coax velocity factor (typical VF ≈ 0.66).

Example for 20 metres (centre ≈ 14.175 MHz):

• Half-wave: 150 / 14.175 ≈ 10.58 m
• Quarter-wave: 75 / 14.175 ≈ 5.29 m
• Quarter-wave coax stub (VF 0.66): 5.29 × 0.66 ≈ 3.49 m

Practical builds for the 20 m design end up around 100 ft (~30 m) long overall. A 10 m version would be roughly half that length — still manageable in many gardens.

Feed and matching options

The centre feed impedance of this collinear is typically around 125 Ω. Practical matching choices are:

• Install a 4:1 balun at the feed point to transform the feed closer to 50 Ω for direct coax connection to the transceiver.
• Run 450 Ω ladder line back to the shack and use an antenna tuner. This avoids a balun and makes the antenna usable across multiple bands (it will tune on higher bands though the designed gain is realised mainly on the target band).

• The design provides its intended gain primarily on the design band (commonly 20 m). Off-band performance will still work but the gain will reduce.
• With ladder feed you can use the antenna on 20 m up to 10 m fairly effectively. Below about 30 m (30 metres band and lower) performance diminishes quickly.
• There is no significant front-to-back ratio — you get gain in two opposite directions but not the directional suppression a Yagi provides.

• Consider mounting as a horizontal wire if you have the space. The inverted-V arrangement is sometimes suggested, but results vary and details need careful attention.
• Use high-quality ladder line and keep it away from conductive surfaces. If you use coax stubs, protect the shorted ends and any soldered joints from weather.
• For a neater installation, coil coax stubs loosely and secure them so they cannot move in the wind.
• VHF collinears often use the same principle but are encapsulated in fiberglass housings; the HF wire collinear is the same idea scaled to HF wavelengths.

1. Decide target band (example: 20 m).
2. Calculate half-wave and quarter-wave lengths (use formulas above).
3. Choose phasing stub type: 450 Ω ladder line or coax (note VF for coax).
4. Prepare two shorted quarter-wave stubs and plan how to coil or route them.
5. Decide feed method: 4:1 balun at the feed point (coax to radio) or 450 Ω ladder line back to a tuner.
6. Install supports so the full length is clear of trees and metal. Aim to raise the wire as high as practical for lower takeoff angle.
7. Tune and test, then adjust stub lengths slightly if necessary to optimise for the band centre.

A three-element horizontal collinear is an elegant, low-cost way to gain a couple of decibels and narrow the beamwidth without a tower or rotator. It won’t replace a high, rotatable Yagi for all applications, but for many backyard stations it provides a meaningful performance step up from a simple dipole — especially on 20 metres — while keeping construction and cost simple.

Good to know: If you want multi-band versatility and are happy to use a tuner, feed with ladder line. If you want a neat coax feed directly to the radio, add a 4:1 balun at the centre. Either way, the collinear is worth considering where a Yagi is not feasible.

For more information please visit our online store or alternaitvely contact us and our team will be happy to assist you.