Dipole Calculator
Find the length of a half-wave dipole antenna.
A half-wave dipole is cut to roughly half the wavelength, with a velocity-factor correction.
How the Math Works
The formula length ≈ 143 ÷ f(MHz) meters is derived from electromagnetic wave physics. A half-wave dipole antenna resonates when its physical length matches half the wavelength of the signal it transmits or receives. Since wavelength (λ) equals the speed of light (≈299,792,458 m/s) divided by frequency (f), a half-wave dipole is λ/2. Accounting for the velocity factor of typical dipole materials (≈0.95), the calculation simplifies to 143 meters per MHz. This approximation allows quick estimation of antenna length for any frequency in megahertz, balancing theoretical accuracy with practical usability for most amateur and professional applications.
Practical Applications
To use this calculator, simply input the operating frequency in megahertz (MHz) and divide 143 by that value to determine the total antenna length in meters. For example, a 100 MHz signal requires a 1.43-meter dipole (each leg would be 0.715 meters if cut symmetrically). This method assumes standard copper wire and typical environmental conditions; however, adjustments may be needed for extremely high or low frequencies, thick conductors, or specific material properties. Always verify measurements with an antenna analyzer for optimal resonance in real-world setups.
Day-to-Day Use
This calculation empowers everyday users, like ham radio enthusiasts or hobbyists, to build efficient antennas for communication, emergency preparedness, or educational projects. For instance, a 27 MHz CB radio antenna would measure ~5.3 meters, enabling better signal clarity without complex tools. It also aids in troubleshooting poor reception on TVs or Wi-Fi routers by estimating optimal antenna lengths. By demystifying antenna design, this formula bridges theoretical physics and practical problem-solving, making technical communication accessible to non-experts in daily life.
Worked example
100 MHz → about 1.43 m total (0.715 m per leg).
FAQ
Why not exactly half a wavelength?
End-effect capacitance makes the resonant length slightly shorter.