Half-Wave Dipole Length
Calculate the physical length of a half-wave dipole, L = (150 ÷ f)·VF, from the frequency f (MHz) and the velocity factor VF (typically ~0.95 for wires, correcting the end effect). The result, in metres, is the total length of the dipole antenna resonant at the desired frequency — each arm is half this value. The half-wave dipole is the most used reference antenna, with 2.15 dBi gain. The velocity factor makes the antenna slightly shorter than a half wavelength in vacuum. Enter the frequency and the velocity factor.
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Half-wave dipole length
The half-wave dipole is the most fundamental and most widely used antenna in radio engineering: two in-line conductors, fed at the center, with a total length close to half a wavelength at the operating frequency. At that size the antenna reaches resonance (its reactance cancels out), presenting a purely resistive impedance of about 73 Ω that is easy to match, plus a gain of 2.15 dBi. The physical length is L = (150 ÷ f)·VF, with f in MHz and the result in meters — each leg of the dipole measures half of that value. The term 150/f is the half wavelength in free space (since λ = 300/f); the velocity factor VF (typically ~0.95 for wire) corrects the so-called end effect: the field at the tips makes the antenna behave as if it were electrically a little longer, so it has to be physically a little shorter than the theoretical half wavelength in order to resonate at the right frequency. That is why the practical formula uses ~0.95 (and thicker or insulated wire calls for a lower VF). Working out the correct length is the first step in building any dipole, from HF wires for ham radio to FM and TV antennas. Enter the frequency and the velocity factor.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.