Fresnel Zone Radius
Calculate the first Fresnel zone radius, r = 17.31·√(d₁·d₂ ÷ (f·(d₁+d₂))), from the distances of each end to the point d₁ and d₂ (km) and the frequency f (GHz). The result, in metres, defines the ellipsoid around the line of sight that must stay clear of obstacles for a radio link to work without diffraction loss. Rule of thumb: at least 60% of the first Fresnel zone should be unobstructed. It is essential in designing point-to-point, microwave and long-range Wi-Fi links. Enter the distances and the frequency.
Result
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Raio da zona de Fresnel
Num enlace de rádio, o sinal não viaja apenas pela linha reta entre as antenas — ele ocupa um volume elipsoidal em torno dessa linha, e ondas que percorrem caminhos ligeiramente diferentes chegam com fases distintas. A primeira zona de Fresnel é o elipsoide onde essas ondas chegam praticamente em fase, reforçando o sinal direto; se um obstáculo (morro, prédio, árvore) invade essa zona, causa difração e perda, mesmo havendo linha de visada limpa. O raio máximo dessa zona (no ponto considerado) é r = 17,31·√(d₁·d₂ ÷ (f·(d₁+d₂))), com as distâncias d₁ e d₂ de cada antena ao ponto em km, a frequência em GHz e o raio em metros. O raio é maior no meio do percurso e em frequências baixas. A regra prática de projeto é manter pelo menos 60% da primeira zona de Fresnel desobstruída para que a perda por difração seja desprezível — por isso enlaces longos exigem antenas altas, que elevam a linha de visada acima dos obstáculos. Informe as duas distâncias e a frequência.
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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.