Calculator
Example Data Table
| Band | Frequency | Directors | Velocity factor | Use case |
|---|---|---|---|---|
| 20 m | 14.15 MHz | 1 | 0.95 | Portable three element wire beam |
| 15 m | 21.20 MHz | 2 | 0.96 | Compact field layout |
| 10 m | 28.40 MHz | 3 | 0.97 | Higher gain temporary beam |
Formula Used
Wavelength: wavelength = speed of light / frequency.
Element length: length = wavelength × element factor × velocity factor × end effect factor.
Boom length: boom length = reflector spacing + director spacings.
Total wire: total wire = element wire + tail allowance + waste allowance.
Wind force: force = 0.5 × air density × drag coefficient × wire diameter × wire length × wind speed squared.
Sag tension: horizontal tension = wire weight per meter × span squared / eight times sag.
How to Use This Calculator
Enter the target frequency first. Select the unit that matches your value.
Choose the number of directors. More directors increase length and support needs.
Edit the element factors when your design uses special proportions.
Add wire diameter, density, wind speed, sag, and cost values.
Press calculate. Review the result above the form.
Download the CSV or PDF file for your build notes.
Wire Beam Antenna Construction Guide
Wire Beam Planning Overview
A wire beam antenna needs careful dimensions before work begins. Small length changes can move the resonant point. Spacing also changes gain, front to back ratio, and feed behavior. This calculator gives a practical construction estimate. It is not a substitute for field tuning. It helps builders cut wires with a clear starting point.
Element Length Decisions
The reflector is usually longer than the driven element. Directors are usually shorter. The calculator uses wavelength factors for each part. You can edit those factors for different designs. A velocity factor and an end effect factor are also included. These values help match real insulated or bare wire behavior. Longer tails can be added for knots, clamps, and final trimming.
Spacing And Support Layout
Element spacing controls the boom or rope layout. A wide spacing may improve bandwidth. A tight spacing may save space. The tool converts wavelength spacing into real distance. It also estimates turning radius. This helps when planning trees, poles, roof points, or temporary field masts. The construction category is useful because supports matter as much as radio values.
Loads And Materials
Wire antennas look light, yet wind can add real force. The calculator estimates wire mass, wind load, and simple sag tension. These are planning values only. Use proper hardware, safe clearances, and local rules. Never place any antenna near power lines. Add a safety factor when choosing rope, eye bolts, and anchor points.
Using The Results
Start with your target frequency. Pick a design with enough directors for your space. Review total wire length and boom length. Compare the turning radius with your available area. Export the results before buying materials. During installation, cut elements slightly long. Then tune the driven element with an analyzer. Adjust supports after the wire has settled.
A Practical Check Before Building
Good records prevent repeated cutting. Keep the exported file with your chosen frequency, factors, and material prices. Measure wire after tension is applied. Mark each element center. Label reflector, driven element, and every director. Use weather resistant knots and strain relief. Recheck measurements after raising the antenna. Final trimming should be small, slow, and even. That approach keeps the layout safer, cleaner, and easier to repair.
FAQs
What is a wire beam antenna?
It is a directional antenna made with wire elements. It often uses a reflector, driven element, and one or more directors. The layout can be supported by rope, poles, trees, or a light boom.
Can this calculator replace antenna modeling software?
No. It gives practical starting dimensions and construction estimates. Modeling software can predict pattern, impedance, and ground effects in more detail. Final tuning is still recommended.
Why is the reflector longer?
A longer reflector sits behind the driven element. It helps push more energy forward. This improves directional behavior and front to back ratio.
Why are directors shorter?
Directors are usually shorter than the driven element. They help pull the main radiation pattern forward. More directors can add gain, but they also add space and support demands.
What does velocity factor mean?
Velocity factor adjusts the physical length of wire. Insulation, wire type, and nearby materials can change resonance. A lower value makes the calculated element shorter.
Should I cut the wire exactly to the result?
Cut slightly long first. Install the antenna, measure resonance, and trim slowly. This prevents overcutting and gives room for knots, clamps, and field adjustments.
Is the wind load result structural proof?
No. It is a simple planning estimate. Use rated hardware, local building guidance, safe clearances, and a good safety factor for real installations.
Can I use this for temporary field antennas?
Yes. It is useful for portable beams, event stations, and quick layouts. Check available space, turning radius, support height, and feed line routing before raising the antenna.