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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Comprimento de dipolo de meia onda
O dipolo de meia onda é a antena mais fundamental e usada da radiotécnica: dois condutores em linha, alimentados no centro, com comprimento total próximo a meia onda da frequência de operação. Nessa dimensão a antena entra em ressonância (sua reatância se anula), apresentando uma impedância puramente resistiva de ~73 Ω, fácil de casar, e um ganho de 2,15 dBi. O comprimento físico é L = (150 ÷ f)·VF, com f em MHz e o resultado em metros — cada braço do dipolo mede metade desse valor. O termo 150/f é a meia onda no vácuo (já que λ = 300/f); o fator de velocidade VF (tipicamente ~0,95 para fios) corrige o chamado efeito de extremidade: o campo nas pontas faz a antena se comportar como se fosse eletricamente um pouco mais longa, então ela precisa ser fisicamente um pouco mais curta que a meia onda teórica para ressoar na frequência certa. Por isso a fórmula prática usa ~0,95 (e fios mais grossos ou isolados pedem VF menor). Calcular o comprimento certo é o primeiro passo para construir qualquer dipolo, dos de HF para radioamadorismo às antenas de FM e TV. Informe a frequência e o fator de velocidade.
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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.