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Link budget is the computation of the whole transmission chain. Here's a budget for free space loss transmission:
- Transmit [dBm]: transmitter power [dBm] -cable loss [dB]+ antenna gain [dBi]
- Propagation [dB]: Free space loss [dB].
- Receive [dBm]: antenna gain[dBi]- cable loss [dB]- receiver sensitivity [dBm]
Link working condition is that the total : Total Transmit + Total Propagation + Total Receive must be greater than 0 . The remain gives the margin of the system.
Warning: These rules are theoretical. It represents the maximum achievable for a system. In reality we will have interferences (other WLAN networks, bluetooth), industrial noise (microwave ovens), atmospheric losses (air moisture, scattering, refraction), badly pointed antenna, reflexions,... that will affect performances. It is so necessary to take a sufficient security margin (5-6 dB or more on large distances).
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