Building a wideband antenna doesn't have to be a guessing game. The discone antenna is one of the most versatile designs for scanners and radio enthusiasts because of its massive bandwidth and omnidirectional pattern. Use the calculator below to determine the exact dimensions for your custom build based on your lowest target frequency.
Calculate Dimensions
Design Specifications
*Calculations based on standard 1/4 wave resonance at the lowest frequency.
What is a Discone Antenna?
The discone antenna is a version of a biconical antenna in which one of the cones is replaced by a disc. It is typically mounted vertically, with the disc at the top and the cone below. It is a "fat" antenna that offers an exceptionally wide frequency range—often covering a 10:1 ratio between the highest and lowest usable frequencies.
How the Calculation Works
The performance of a discone is primarily governed by the dimensions of the cone. To ensure the antenna works at your lowest desired frequency, the length of the cone elements must be approximately a quarter-wavelength of that frequency.
- Cone Length (L): This is the slant height of the cone. The standard formula is 75 divided by the frequency in MHz (for meters) or 2953 divided by frequency (for inches).
- Disc Diameter (D): For optimal impedance matching, the disc should be approximately 67% to 70% of the cone's slant length.
- The Gap (G): The distance between the disc and the apex of the cone is critical for the SWR (Standing Wave Ratio). It is typically kept very small, often determined by the insulator used.
Materials for Construction
If you are building this at home, you have several options for materials:
- Solid Sheet Metal: Provides the best performance but has high wind resistance.
- Wire Spoke (Radial) Design: The most common DIY method. Using 8 to 16 copper or stainless steel rods to simulate the solid surfaces of the disc and cone.
- Copper Pipe: Excellent for the central support structure and for larger, lower-frequency antennas.
Installation Tips
Because the discone is an omnidirectional antenna, it should be mounted as high as possible and away from other metallic structures. Since it is unbalanced, using a 1:1 choke balun or simply winding a few turns of the coaxial cable near the feed point can help prevent the outer shield of the cable from becoming part of the antenna system.