Low Noise Multi-band HF Antenna for Small Gardens

VIDEO

A compact, low-noise loop that works on multiple HF bands can be a perfect solution when space and local electrical noise are limiting factors. The delta loop—a triangular full-wave loop often hung in a diamond shape—offers a small footprint, straightforward installation and the quiet receive performance loop antennas are known for.

A delta loop is a full-wavelength loop antenna arranged as a triangle (often hung as a diamond). A loop does not need to be circular: square, triangular or diamond shapes all behave similarly electrically for practical HF use. On its fundamental frequency the loop is a full wavelength around, so each side of a triangular loop is roughly one third of a wavelength.

• Low noise: loops tend to pick up less local electrical noise than many other antennas, making them attractive in urban environments.
• Small footprint: a 20m delta loop only needs about a 20–25 ft top span, so it suits small gardens.
• Multiband potential: loops operate on harmonics, so one loop can cover several HF bands.
• Simple supports: the triangular shape makes it easier to support with two or three points compared with some other full-wave loops.

Use the wavelength formula to calculate dimensions:

Where,

λ = Wavelength (Metres)

f = Frequency (MHz)

For a triangular (delta) full-wave loop, each side is approximately one third of that wavelength.

Example for a 20m-centred design: a practical full-wave loop length is often quoted around 20–21 m (≈66–69 ft), which gives each side ≈6.7–7.0 m (≈22–23 ft). Adjust the exact length to tune the loop to your desired operating frequency.

Height affects takeoff angle and gain just like any other HF antenna: higher is generally better. But one of the delta loop’s advantages is usable performance even when the lower vertex is only a few feet above ground.

• A top horizontal span of around 20 ft can be supported by two trees, a short mast and a fence post, or a small rooftop anchor.
• If you can raise the top to around 25 ft the pattern improves, but a bottom vertex 3–4 ft above ground still yields useful performance.
• Lower heights favour higher-angle radiation (good for NVIS), while higher installations give lower-angle radiation useful for DX.

There are a few practical ways to feed a delta loop. Choose the method that best matches your band plan, noise situation and available matching equipment.

Feeding the loop at the bottom vertex with a 4:1 balun is a common approach. The feedpoint impedance there typically sits around ~125 ohms, so a 4:1 balun brings that closer to 50 ohms and eases matching to coax.

If you only want to use the antenna on one band, you can insert a quarter-wave length of 75 ohm coax between the loop feed and a 1:1 balun to transform the impedance for a single-band match. This locks the antenna to that band but simplifies the feed.

For true multiband use, run 450 ohm ladder line (or similar balanced feedline) from the feedpoint back to the shack and then use a 4:1 balun (or an ATU) at the shack end. Ladder line has low loss even with a high SWR, so it is ideal when the loop will be used on multiple harmonics.

Practical expectations:

• You will likely see VSWRs of around 1.5:1 on some bands and up to 2:1 on others when using a simple 4:1 balun into coax. An ATU can tidy up the match.
• Coax losses for a typical run (40–50 ft) add roughly 1 dB or so at HF; ladder line losses will be substantially lower for the same mismatches.

A full-wave loop radiates on its harmonics. That means a loop cut for 20m will also work on 10m (the second harmonic) and other intermediate harmonics. Likewise, if you feed the same loop as a 40m electrical length (using a matching section), you can access 40, 20, 15 and 10 m.

Be aware that the radiation pattern changes when you operate on harmonics. Lobes and nulls appear in different directions, so takeoffs and DX performance vary band to band. That said, many operators report surprisingly good DX from low-installed delta loops despite these pattern changes.

• Gain: roughly +1 dB over a centre-fed dipole on the fundamental—useful but not dramatic.
• Directivity: on the fundamental the main lobe is broadside to the plane of the loop, similar to a dipole.
• Noise: loops typically exhibit lower pickup of local electrical noise, making the delta loop one of the quietest options for receive in noisy areas.
• DX: many users report good DX performance even with modest installation heights.

1. Calculate the full-wave length with `wavelength (m) = 300 / frequency (MHz)` and divide by 3 for each triangular side.
2. Use insulated wire rated for outdoor use—copper or copper-clad steel is common.
3. Install three support points or a top horizontal support plus two lower tie-offs to form a diamond or triangle shape.
4. Choose your feed method: 4:1 balun at the feedpoint with coax, or ladder line back to an ATU in the shack for multiband use.
5. Weatherproof baluns and connections with tape and silicone where appropriate; keep ladder line separated from conductive structures on the run to the shack.
6. Start with the antenna slightly long. Trim gradually to resonance at your target frequency.
7. Monitor SWR on each band and use the ATU to refine the match if needed.

• Quiet receive performance in noisy environments
• Small garden friendly
• Multiband coverage with harmonics
• Relatively simple to erect and support

• Requires a balun or ladder line and an ATU for best multiband performance
• Radiation pattern can be complex on harmonics (lobes and nulls)
• Not a huge gain increase over a dipole—expect modest improvement

1. Cut wire for a full-wave loop around the 20m region: each side roughly 6.7–7.0 m (≈22–23 ft).
2. Form a diamond with a top horizontal span of ~6.7 m and two lower legs forming the pyramid/diamond shape.
3. Attach a short length of 450 ohm ladder line at the bottom vertex and run it back to the shack.
4. At the shack install a 4:1 balun or use an ATU to match to 50 ohm coax feeding your transceiver.
5. Trim and tune the loop on the fundamental and check harmonic bands for usable SWR and pattern.

The delta loop is a compact, low-noise, multiband HF antenna that suits small gardens and noisy environments. It offers modest gain, simple supports and the flexibility to cover several bands when fed with ladder line. If space and local noise are key constraints, the delta loop is well worth building and testing—many operators find its quiet receive and surprising DX performance a great trade-off for the small footprint.

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