Understanding the Discone Antenna: For Amateur Radio Satellite Reception

A discone antenna is an exceptionally wideband, omnidirectional antenna that looks exactly like its name suggests: a flat metal disc mounted horizontally above a metal cone, separated by an insulator. While they are legendary in the amateur radio world for general VHF/UHF scanning, they have a major physical limitation when it comes to tracking Low Earth Orbit (LEO) satellites.

Here is a breakdown of how they work and why they behave the way they do for satellite reception.

How the Discone Works

• Massive Bandwidth: A properly built discone offers a frequency range ratio of up to 10:1. A single antenna can easily cover everything from the 2m band (144 MHz) straight through the 70cm band (430 MHz) and well beyond, making it incredibly convenient for sweeping multiple bands without changing hardware.
• The Geometry: The feed point is at the center of the disc. Usually, the center conductor of a 50-ohm coaxial cable connects to the top disc, while the outer shield connects to the cone. (For lower frequencies, hobbyists often build the disc and cone out of stiff wire or rods to reduce wind load).
• Polarization: It is vertically polarized, matching most terrestrial FM voice communications.

The Problem for Satellite Reception: The Zenith Null

If you look at the radiation pattern in the image above (the red “apple” shape), you will notice two things:

1. Strong at the horizon: The antenna’s sensitivity is concentrated outward, parallel to the Earth. It does a great job picking up signals far away on the horizon.
2. Deaf at the top: There is a massive “hole” or null pointing straight up into the sky.

When an amateur radio satellite first comes over the horizon, a discone will pick it up fairly well. However, as the satellite climbs higher in the sky and reaches its closest point to you—directly overhead (the zenith)—the signal enters that null. Just when the satellite should be at its strongest and clearest, the discone goes nearly deaf to it.

The Verdict for LEO Operations

If you want a single, fixed antenna on your roof to listen to local repeaters, air traffic control, and occasionally catch a low-elevation satellite pass, a discone is fantastic.

However, if your primary goal is working LEO satellites, relying on a fixed omnidirectional antenna will lead to deep fading during the best parts of the pass. You are much better off using a directional antenna that you can point directly at the bird. A compact, handheld directional beam—like a Moxon-Yagi hybrid or an Arrow antenna—will give you the gain you need to hear the satellite clearly through its entire arc, completely bypassing the zenith null issue.