Advanced Calculator
Example Data Table
| Band | Frequency | Approx Full Wave Wire | Equilateral Side | Approx Height |
|---|---|---|---|---|
| 40 m | 7.100 MHz | 40.11 m / 131.59 ft | 13.37 m / 43.86 ft | 11.58 m / 37.99 ft |
| 20 m | 14.200 MHz | 20.06 m / 65.79 ft | 6.69 m / 21.93 ft | 5.79 m / 19.00 ft |
| 10 m | 28.400 MHz | 10.03 m / 32.90 ft | 3.34 m / 10.97 ft | 2.90 m / 9.50 ft |
Example values are planning estimates. Real antennas need final trimming after installation, because height, soil, supports, wire type, and nearby objects affect resonance.
Formula Used
The calculator starts with the radio wavelength. It uses this formula:
Wavelength in meters = 299.792458 / frequency in MHz
For a common full wave delta loop, the first wire estimate is:
Loop length = wavelength × loop wavelength factor
The calculator then adjusts the wire length with velocity factor, shortening trim, and sag allowance:
Final cut length = wavelength × loop factor × velocity factor × (1 - trim %) × (1 + sag %)
For an equilateral delta loop, each side equals one third of the final wire length:
Side = final cut length / 3
The equilateral triangle height is:
Height = side × √3 / 2
For a custom triangle, the calculator divides total perimeter by the side ratios. It then uses Heron’s formula to estimate triangle area and height.
How to Use This Calculator
- Enter the operating frequency in MHz.
- Keep loop wavelength factor at 1 for a normal full wave loop.
- Set velocity factor for your wire and insulation type.
- Add a small trimming percent if you prefer cutting slightly short.
- Add sag allowance if your support system will not hold straight sides.
- Choose equilateral, isosceles, or custom ratio shape.
- Select the feed point and feedline impedance.
- Press the calculate button and review the result above the form.
- Use CSV or PDF download for saving the project data.
Delta Loop Antenna Planning Guide
What This Tool Calculates
A delta loop antenna is a closed wire loop shaped like a triangle. It is often used on HF bands because it can work well with simple supports. This calculator estimates the total wire length, side lengths, height, and matching information. It is designed for planning before cutting wire.
Why Frequency Matters
The antenna length depends mainly on wavelength. Lower frequencies need longer wire. Higher frequencies need shorter wire. A full wave loop uses about one wavelength of wire. This is the normal starting point for many delta loop designs.
Shape and Support Choices
An equilateral loop gives balanced side lengths and a clean layout. An isosceles loop is useful when the top support is high, but the base must fit a limited space. A custom ratio helps builders match real trees, masts, poles, or roof points. The calculator checks impossible triangle values and adjusts unsafe entries.
Trimming and Installation
Real installations rarely match math perfectly. Wire insulation, nearby buildings, soil, feedline route, and support height can shift resonance. For that reason, many builders cut a little long, test the antenna, then trim slowly. This calculator includes trim and sag fields, so you can plan more carefully.
Feed and Matching Notes
A delta loop feed point changes impedance and radiation behavior. Corner feeding is common. It can favor vertical polarization when installed with the right orientation. Center feeding on a side may change current distribution and feed impedance. The impedance values shown here are practical estimates, not guaranteed analyzer readings.
Best Practical Workflow
Start with your chosen frequency. Pick the closest shape to your real support points. Calculate the dimensions. Cut the wire with enough room for final adjustment. Install the loop safely and measure it with an analyzer. Trim small amounts from the wire until the resonant point moves where you need it. Save the final values for future rebuilds.
FAQs
1. What is a delta loop antenna?
It is a closed wire antenna shaped like a triangle. It is usually built as a full wave loop for one band. Many operators use it on HF because it can provide efficient radiation with simple supports.
2. Is a delta loop always one full wavelength?
A common resonant delta loop is close to one full wavelength. The calculator lets you change the loop wavelength factor for experiments, harmonic work, or nonstandard designs.
3. Should I cut the wire exactly to the calculated length?
It is safer to cut slightly long, install the loop, measure resonance, then trim slowly. Nearby objects, support height, wire coating, and ground conditions can change the final resonant frequency.
4. What velocity factor should I use?
Bare wire is often near one. Insulated wire can be lower. Use your wire data when available. If you are unsure, start near 0.95 and leave extra wire for final adjustment.
5. Which feed point is best?
There is no single best point. Corner feed is popular. Apex and side feed options may change impedance and polarization. Choose the feed point that matches your support layout and operating goal.
6. Why does the calculator show SWR only as an estimate?
The SWR estimate assumes a simple resistive load. Real antennas include reactance, ground effects, support coupling, and feedline interaction. Use an antenna analyzer for reliable tuning.
7. Can I use this calculator for inverted delta loops?
Yes. The same perimeter and side length math applies. Inverted orientation changes support points and may change radiation behavior, but the basic wire length calculation remains useful.
8. Why include a sag allowance?
Wire sides rarely stay perfectly straight. Sag increases physical wire used between supports. A small allowance helps the cut length match the installed antenna more closely.