Calculation Results
About This Calculator
Calculate center-fed half-wave wire dipole total length, quarter-wave leg dimensions, velocity end-effect factor, and bandwidth for Ham radio (HF/VHF/UHF).
Frequently Asked Questions
Why is 468 used in the wire dipole formula instead of 492?
The speed of light in free space yields 492 / f(MHz) for a theoretical half wavelength. In real wire antennas, capacitive end-effect and conductor velocity factor slow electromagnetic wave propagation by approximately 5%, resulting in the standard formula: Length (feet) = 468 / f(MHz).
What is the nominal feedpoint impedance of a center-fed half-wave dipole?
In free space or elevated at least a half-wavelength above ground, a resonant half-wave dipole has an impedance of approximately 73 ohms resistive, providing an excellent match to standard 50-ohm coaxial cable with an SWR under 1.5:1.
Why should a 1:1 current balun be installed at the dipole feedpoint?
A 1:1 current balun transitions between the balanced antenna dipole legs and the unbalanced coaxial line, preventing RF currents from traveling down the outside of the coax shield which causes RF in the shack and audio distortion.
How does height above ground affect dipole radiation pattern?
At heights below 0.25 wavelength, ground reflection directs radiation straight upward (Near Vertical Incidence Skywave, NVIS) for local contacts. Raising the antenna to 0.5 wavelength or higher flattens the pattern to a low 15°–25° take-off angle ideal for worldwide DX.