delta loop calculator

What this delta loop calculator does

A delta loop is one of the most practical wire antennas for HF operation. This calculator gives you a solid starting point for building a one-wavelength loop in a triangular shape. Instead of guessing cut lengths, you can quickly generate values for total perimeter and side length in both feet and meters.

The calculation uses a standard full-wave loop constant and then applies your selected velocity factor. Because real installations are affected by environment, insulation, feed system, and height above ground, the final dimensions are best treated as a starting estimate, not a final cut-and-forget number.

Delta loop formula used

Core equation

The calculator starts with the common full-wave loop approximation:

Perimeter (feet) = 1005 ÷ Frequency (MHz)
Perimeter (meters) = 306.3 ÷ Frequency (MHz)

Then it applies your velocity factor (VF):

Adjusted Perimeter = Theoretical Perimeter × VF

For an equilateral delta loop:

Each side length = Adjusted Perimeter ÷ 3

How to use this calculator effectively

• Pick a center frequency: For a voice segment or CW segment, choose the middle of the range you care about most.
• Choose realistic VF: If you are unsure, start at 0.95 for insulated wire and tune from there.
• Add slack: A 1%–3% margin helps avoid cutting wire too short on your first attempt.
• Tune after installation: Final resonance shifts once the antenna is in its actual mounting position.

Build and installation tips

1) Feed point and polarization

A delta loop can be fed at different points depending on your goal. Feeding from a lower corner often favors vertical polarization components, while feeding from the middle of a horizontal wire can encourage horizontal polarization. Pattern and takeoff angle also vary with mounting height and surroundings.

2) Height matters

Raising the loop usually improves performance and can reduce losses from nearby objects. Keep the wire clear of roofs, gutters, metallic masts, and power lines. Even a few extra feet of elevation can noticeably change SWR and radiation pattern.

3) Matching and feedline

Many operators feed delta loops with 50-ohm coax through a balun or common-mode choke at the feed point. If your measured impedance differs from expectation, feed point position and loop geometry can often be adjusted before adding complex matching networks.

Worked example

Suppose you want a 20-meter band delta loop centered at 14.2 MHz, using insulated wire with VF 0.95:

• Theoretical perimeter (m): 306.3 ÷ 14.2 = 21.57 m
• Adjusted perimeter (m): 21.57 × 0.95 = 20.49 m
• Each side (m): 20.49 ÷ 3 = 6.83 m

If you add 2% cutting slack, cut to about 20.90 m total wire and trim gradually during on-air tuning.

Common mistakes to avoid

• Cutting exactly to theoretical length with no trim margin.
• Ignoring insulation effects on electrical length.
• Tuning at ground level, then installing much higher and expecting the same SWR.
• Skipping current choke, which can cause feedline radiation and unstable measurements.
• Trying to optimize all bands at once without prioritizing a primary operating range.

Quick FAQ

Is this only for amateur radio?

It is intended for RF antenna planning in general, but the examples are geared toward HF amateur radio use.

Can I use this for a square loop?

The perimeter estimate is still useful, but side-length output assumes a triangular delta loop. For square loops, divide perimeter by four instead of three.

Will this guarantee a perfect 1:1 SWR?

No calculator can guarantee that. Nearby structures, wire routing, soil, feedline, and balun/choke quality all matter. Use this as a high-quality starting point and finish with real measurements.

Final note

A delta loop is simple, efficient, and surprisingly versatile. With careful measurements and a little tuning time, you can build a robust antenna that performs extremely well for local and DX work. Use the calculator above to start with confidence, then let on-site testing refine your final dimensions.