Counterpoise Calculator

The Counterpoise Calculator computes quarter-wave radial lengths, total wire requirements, and estimated ground efficiency ($eta$) for antenna counterpoise and ground radial systems. Vital for HF quarter-wave vertical monopoles and end-fed antennas, an optimized counterpoise minimizes soil return loss and maximizes radiated signal power.

Enter Frequency, Number of Radials exactly in the units shown by this counterpoise. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.

• Frequency — use MHz.
• Number of Radials.

The results describe the calculated counterpoise values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.

The Counterpoise uses λ = 300/f, Quarter-wave = 75/f, Half-wave = 150/f. Supply Frequency (MHz), Number of Radials in the displayed units, then use the calculated values as the first engineering target for this ground & radial system design or analysis.

A quarter-wave vertical monopole requires a low-resistance RF return path to function effectively. An artificial ground plane—or counterpoise—provides this return path. Ground loss resistance ($R_g$) operates in series with the antenna radiation resistance ($R_r$). Increasing the number of radial wires lowers $R_g$, elevating overall antenna radiation efficiency: $\eta = [R_r / (R_r + R_g + R_l)] \times 100\%$. Elevated counterpoise radials require resonant tuning (quarter-wavelength), whereas buried or ground-contact radials detune due to earth capacitance, making quantity more critical than exact resonant length.

For elevated counterpoises, raise radials at least $2\text{ to }3\text{ meters}$ above the soil and use 4 to 8 tuned quarter-wave wires. For ground-level or buried radial systems, deploy 16 to 64 radials laid radially around the base; ground coupling makes length non-critical ($0.1\lambda\text{ to }0.25\lambda$ is typical). Connect all radial wires to a heavy ground plate or central hub, and install a current 1:1 choke balun on the main feedline to prevent RF return currents from flowing back along the outer coaxial shield.