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Discone calculator

What it is good at

A discone covers roughly a ten-to-one frequency range with nothing to tune, which is exactly why it ends up on scanners and monitoring stations. The lower edge sets the size: the cone slant length is a quarter wave there. The upper edge then looks after itself.

gapDAB
The slant of the cone is a quarter wave at the lowest frequency; above that a discone works up to roughly 10·fmin
Lower operating frequency (MHz)
Cone half-angle (°)
Number of cone spokes
Dimensions
A — cone slant length (λ/4)
D — disc diameter (0.7·A)
B — cone base diameter
Cone height
Disc-to-cone gap
Length of one spoke
Band
Operating band
Wavelength at the lower frequency

📐 The formulas​

A — cone slant length = λ/4 at the lower frequency
D — disc diameter     = 0.7 × A
B — base diameter     = 2 × A × sin(half-angle)
cone height           = A × cos(half-angle)
disc-to-cone gap      — a few millimetres; it sets the match
Upper edge            ≈ 10 × f_lower

The cone half-angle is usually 25…40°; 30° is a sensible default.

Symbols:​

  • f_lower — the lowest frequency at which the antenna still works
  • Spokes stand in for a solid cone: eight will do, sixteen is better
Where this calculator stops:
  • The 0.7 disc factor and the λ/4 slant are classic rules of thumb, not an exact calculation
  • The disc-to-cone gap is an estimate; in practice you trim it for SWR
  • The pattern hugs the horizon only near the lower frequency; higher up the lobe lifts
  • Fewer than eight spokes spoils the match at the top of the range — the calculator warns you

🎯 In practice​

  • A scanner antenna. One discone instead of five separate antennas.
  • Airband and VHF monitoring. 100–1000 MHz from a single structure.
  • A measurement antenna. Predictable behaviour over a wide range beats gain.
Practical advice:
  1. A discone is a receiving antenna by nature. It will transmit, but it has no gain to offer.
  2. Spokes can be stiff wire or aluminium tubing — you do not need a solid cone.
  3. Hold the gap with an insulator (PTFE, FR-4), not by eye with air.
  4. The connector goes at the bottom: centre conductor to the disc, braid to the cone. Getting that backwards is easy, and the antenna simply will not work.

© 2026 UR3PKI · CyberDev.Space · Content licensed under CC BY-NC-SA 4.0.

How to cite this calculator
UR3PKI. «Discone calculator». CyberDev.Space. https://cyberdev.space/en/radio/calculators/antennas/discone (licence CC BY-NC-SA 4.0).

The licence lets you use this material freely, including in teaching materials, but only with attribution to the author and a link to the source.

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