Free Space Path Loss (FSPL)
Calculate the free space path loss (FSPL), L = 20·log₁₀(d) + 20·log₁₀(f) + 32.44, from the distance d (km) and the frequency f (MHz). The result, in dB, is the attenuation a radio signal suffers simply by spreading through space, with no obstacles — proportional to the square of distance and frequency. It is the central term of any link budget: the greater the distance or frequency, the higher the loss and thus the more power or antenna gain needed. The 32.44 constant applies for km and MHz. Enter the distance and the frequency.
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Perda no espaço livre (FSPL)
Quando uma onda de rádio se propaga no espaço livre (sem obstáculos, reflexões ou absorção), sua potência se dilui à medida que se espalha por uma superfície esférica cada vez maior — a densidade de potência cai com o quadrado da distância. A perda no espaço livre (FSPL) quantifica essa atenuação: L = 20·log₁₀(d) + 20·log₁₀(f) + 32,44, com a distância d em km, a frequência f em MHz e o resultado em dB. Note que a perda aumenta tanto com a distância quanto com a frequência — sinais de frequência mais alta (como 5G em ondas milimétricas ou enlaces de satélite na banda Ka) sofrem perdas muito maiores e exigem antenas mais diretivas. A FSPL é o termo dominante no cálculo de enlace (link budget): parte-se da potência irradiada (EIRP), subtrai-se a FSPL e as demais perdas, somam-se os ganhos das antenas, e verifica-se se o sinal que chega supera a sensibilidade do receptor com folga (margem de desvanecimento). A constante 32,44 é o fator de conversão de unidades para km e MHz (seria 92,45 para km e GHz). Informe a distância e a frequência.
Related Tools
EIRP (Effective Radiated Power)
Calculate the equivalent isotropically radiated power (EIRP), EIRP = P_tx + G − L, adding the transmitter power P_tx (dBm) to the antenna gain G (dBi) and subtracting cable and connector losses L (dB). The result, in dBm, is the power a theoretical isotropic antenna would need to radiate to produce the same power density in the direction of the real antenna's maximum gain. It is the quantity regulated by telecom authorities (legal EIRP limits) and the transmit-side starting point of a link budget. Enter the transmitter power, the antenna gain and the losses.
Fade Margin
Calculate the fade margin, M = P_rx − S, subtracting the receiver sensitivity S (dBm) from the received power P_rx (dBm). The result, in dB, is the slack between the arriving signal and the minimum the receiver can demodulate — the reserve available to absorb temporary fades caused by rain, multipath, vegetation and atmospheric variations. Reliable links typically require margins of 10 to 30 dB, depending on the desired availability and environment. It is the final check of a radio link budget. Enter the received power and the receiver sensitivity.
Radio Link Budget Calculator
Calculate the link budget of a radio link in dB by adding transmit power and gains, then subtracting path losses. Useful for radio communication projects.
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.