delta loop antenna calculator

What this delta loop calculator gives you

A delta loop is a full-wave loop antenna shaped like a triangle. This calculator helps you quickly estimate:

• Total loop circumference (wire length needed)
• Side length for an equilateral triangular loop
• Triangle height
• A cut-long length so you can trim for resonance in the real world

It is designed to be simple, practical, and good enough for first-pass construction before final tuning with an antenna analyzer.

Core formulas used

1) Wavelength from frequency

Free-space wavelength is calculated from frequency:

• Wavelength (meters) = 299.792458 / Frequency (MHz)

2) Loop perimeter

A resonant full-wave loop is approximately one wavelength in circumference. We apply a wire shortening factor for real wire insulation and nearby effects:

• Loop perimeter = wavelength × velocity/shortening factor

3) Equilateral delta loop geometry

For an equilateral triangular loop:

• Side length = perimeter / 3
• Triangle height = side × √3 / 2

How to use the calculator

1. Enter your target operating frequency (for example 7.15 MHz or 14.2 MHz).
2. Select frequency units (Hz, kHz, or MHz).
3. Set a velocity/shortening factor. A value around 0.95 is a common starting point.
4. Add a trim percentage (for example 2%).
5. Click Calculate and cut your wire to the recommended cut-long value.

After installation, trim gradually to move resonance upward in frequency. Always trim both sides evenly when possible.

Practical build notes

Feed point and impedance

Delta loops often present feed impedances that vary with feed location, height above ground, wire diameter, and surrounding objects. Many builders use a balun or matching transformer depending on measured feedpoint impedance.

Orientation and polarization

A vertical triangle can produce useful low-angle radiation for DX when fed appropriately, while different feed positions can alter polarization behavior and current distribution. Treat this as part of your tuning process, not a fixed rule.

Height matters a lot

Even a well-cut loop can shift once installed near trees, metal gutters, masts, or rooftops. Raise the antenna to intended height before final trimming, and re-check SWR across your desired band segment.

Example: 20 meter band starting point

If you target 14.2 MHz with a shortening factor of 0.95, you will get a practical perimeter estimate around one wavelength times that correction. The tool will provide both meters and feet, plus side dimensions for layout in the yard.

Troubleshooting tips

• If resonance is too low in frequency, the loop is electrically too long: trim in small increments.
• If resonance is too high, add wire or reduce trimming.
• Use an analyzer at the feed point to avoid coax-induced measurement confusion.
• Keep feedline routing away from the loop when testing, and use a choke where appropriate.

Important: This calculator provides a strong starting estimate, not a final guarantee. Real-world tuning is always required for best performance.