Tools you might need next
Convert between RF frequency and wavelength in meters and feet. Essential for antenna design and ham radio band planning.
Calculate Standing Wave Ratio from forward and reflected power readings. Convert SWR to return loss and reflected power percentage.
Calculate coaxial cable RF signal loss in dB from cable type, run length, and frequency. Estimate transmit power delivered to your antenna.
Classic formula for wire dipole in free space. Each leg = total ÷ 2. Adjust shorter for insulated wire (velocity factor 0.95–0.98).
Total length (ft) = 468 ÷ Frequency (MHz)Quarter-wave vertical over ground plane. Ground radials improve efficiency. Multiply by velocity factor for coated or thick wire.
Length (ft) = 234 ÷ Frequency (MHz)Insulated wire: VF ≈ 0.95. Bare copper: 0.98–1.0. Coaxial elements use cable VF (typically 0.66–0.85).
Physical length = Calculated length × Velocity factorUpdated: July 2026
468 ÷ 7.150 = 65.5 ft total, 32.75 ft per leg. Trim 2–3% shorter and tune with SWR analyzer for lowest SWR at operating frequency.
234 ÷ 146 = 1.60 ft (19.2 inches) radiator length for quarter-wave ground plane with four radials.
Calculate separate dipole lengths for 80m, 40m, 20m segments connected to common feedpoint — each leg pair cut to band center frequency.
Antenna element length is inversely proportional to frequency. Enter operating frequency and wire type to calculate half-wave dipole total length, each leg length, and quarter-wave vertical with velocity factor correction for insulated wire.