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.
Result
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Margem de desvanecimento (fade margin)
Um cálculo de enlace pode mostrar que o sinal em média chega forte o suficiente — mas a propagação de rádio não é constante. Chuva, neblina, multipercurso (o sinal chegando por vários caminhos refletidos que ora se reforçam, ora se cancelam), vegetação que balança e variações na atmosfera fazem o nível recebido flutuar ao longo do tempo. A margem de desvanecimento (fade margin) é a reserva projetada para sobreviver a essas quedas: M = P_rx − S, a diferença entre a potência recebida P_rx (dBm) e a sensibilidade do receptor S (dBm, o nível mínimo que ele consegue demodular com a taxa de erro aceitável). O resultado, em dB, é o quanto o sinal pode cair antes que o enlace deixe de funcionar. Uma margem de 0 dB significa enlace no limite — qualquer desvanecimento o derruba. Na prática, enlaces confiáveis são projetados com margens de 10 a 30 dB, escolhidas conforme a disponibilidade desejada (99,9%? 99,99%?), a distância, a frequência e o clima da região (chuva intensa exige margens maiores, sobretudo acima de 10 GHz). A margem de desvanecimento é, portanto, a verificação final de um link budget: depois de contabilizar EIRP, perdas e ganhos, confirma-se que sobra folga suficiente. Informe a potência recebida e a sensibilidade do receptor.
Related Tools
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.
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.
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.
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.