Counterpoise and Radials

Counterpoise

A counterpoise is a more general term for any conductor that provides a return path for the antenna's current, especially when there's no real earth ground.

• Often a single wire, or a few wires, tuned or not.
• Common in:
  • End-fed antennas (EFHW, long wire, etc.)
  • Portable setups where a true ground is unavailable

Think of it like this:

• You're “completing the circuit” so the antenna has something to push against.

A counterpoise is a network of suspended horizontal wires or cables (or a metal screen), used as a substitute for an earth (ground) connection in a radio antenna system. It is used with radio transmitters or receivers when a normal earth ground cannot be used because of high soil resistance or when an antenna is mounted above ground level. It usually consists of a single wire or network of horizontal wires, parallel to the ground, suspended above the ground under the antenna, connected to the receiver or transmitter's "ground" wire.

The size of the counterpoise used for radio work depends on the wavelength of the transmit frequency. With a monopole antenna, the counterpoise functions as a ground plane, reflecting the radio waves radiated downward by the antenna. To perform adequately, the counterpoise should extend at least half a wavelength from the antenna tower in all directions.

Some use Faraday fabric as a ground plane to enhance an antenna's performance. However, only if it is electrically connected to the antenna and if it is a decent size will it act as a counterpoise. It is generally too resistive and not designed to carry current effectively.

Radials

Radials are a specific kind of counterpoise, typically used in vertical antenna systems to provide an efficient return path for RF current.

Types of radials:

• Ground-mounted vertical: Needs lots of long radials (16 or more is great, even better if they're 1/4 wavelength).
• Elevated vertical: Fewer radials needed (2–4), but they must be resonant.

In the case of ground-plane antennas or vertical monopoles, radials or a ground plane system is used to improve the antenna's performance by providing a counterpoise or ground reference. Without radials, the antenna would lack an efficient ground reference, which can lead to decreased performance.

Radials are the traditional approach for establishing a ground plane. These are wires extending outward from the base of the antenna, lying on or buried just below the ground surface. They influence the radiation pattern of the antenna. They can also help in impedance matching, especially for quarter-wave monopole antennas. By adjusting the length and number of radials, you can fine-tune the antenna's impedance to match the desired value.