discone antenna calculator

What this discone antenna calculator does

A discone is a wideband, omnidirectional antenna made from a flat disc over a conical section. It is popular for scanner use, VHF/UHF monitoring, amateur radio receiving, and general broadband listening. This calculator gives you practical first-pass dimensions based on commonly used discone design ratios.

The key design target is the lowest frequency you want to cover. Most physical dimensions are derived from that number, because the low-end frequency sets the required antenna size.

Design equations used

Core geometry

• Wavelength: λ = 300 / f (MHz)
• Cone slant length: L = 0.25 × λ × velocity factor
• Disc diameter: D_disc ≈ 0.7 × L
• Cone base diameter: calculated from slant length and cone angle
• Feed gap: starting estimate of about 0.008 × λ

These are widely used approximation formulas for building a workable broadband discone. Fine-tuning is still recommended with an antenna analyzer for best SWR over your specific band of interest.

How to use the dimensions

1) Build the cone

Cut your cone radials to the calculated slant length. Space them evenly around the feed hub. More radials generally improve uniformity and mechanical stability.

2) Build the disc

The top disc can be made as a solid plate, ring, or radial spokes. Keep the effective diameter close to the calculated value.

3) Set the feed gap

Keep a small, consistent gap between the disc and cone apex/feed point. This gap has a real effect on impedance match, especially around the low end.

4) Mounting and feedline

• Use 50-ohm coax (such as RG-58, RG-8X, or better low-loss cable for long runs).
• Mount as high and clear as possible, away from nearby metal objects.
• Weatherproof the feed point and connector transitions.

Practical tuning tips

• If low-end match is poor, slightly increase cone length or adjust feed gap.
• If high-end behavior is uneven, improve mechanical symmetry and radial spacing.
• Use an antenna analyzer sweep to validate across your intended frequency range.
• Small physical changes can significantly improve broad coverage.

Example use case

Suppose you want to cover airband and public service monitoring from around 118 MHz upward. Enter 118 MHz as your low frequency, choose an apex angle near 60°, and start with 8 to 12 cone radials. The calculator outputs dimensions in meters, centimeters, and inches so you can build from local materials.

Important notes and limitations

This calculator provides engineering starting dimensions, not guaranteed final resonance. Real-world performance depends on conductor diameter, mounting mast interaction, nearby structures, connector transitions, and construction accuracy.

For mission-critical transmitting use, verify your build with a calibrated analyzer and follow local RF safety guidelines.