Wireless Link Budget (EIRP and Fade Margin)

The full point-to-point RF link budget: EIRP, received power, and fade margin.

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Details, formula, and sources

EIRP = Pt + Gt - Lcable(tx); the received power Prx = EIRP - FSPL + Gr - Lcable(rx) with FSPL = 32.44 + 20 log10(d_km) + 20 log10(f_MHz); the fade margin = Prx - the receiver sensitivity is the headroom against rain, multipath, and misalignment. A 20 dBm radio with 12 dBi antennas and 1 dB of cable each end over a 1 km 2.4 GHz path into a -80 dBm receiver delivers -58 dBm for a 22 dB fade margin. Aim for at least 10 dB of margin (20+ dB for a carrier-class or long/rainy link); near zero will not hold up. Free space only - rain/atmospheric attenuation, obstruction and Fresnel diffraction, and interference are separate. Per Friis / ITU-R P.525. A planning estimate; the path survey and a commissioning test govern.

EIRP = Pt + Gt - Lcable(tx); FSPL = 32.44 + 20 log10(d_km) + 20 log10(f_MHz); Prx = EIRP - FSPL + Gr - Lcable(rx); fade margin = Prx - Rx sensitivity. All in dB; target margin >= 10 dB.

The point-to-point wireless link budget - EIRP, free-space path loss, and fade margin - from the Friis transmission equation / ITU-R P.525, by name; first-principles dB accounting.

The link-budget dB accounting and the Friis / FSPL relation are public first-principles RF (ITU-R P.525 is a free ITU download); the powers, gains, cable losses, distance, frequency, and receiver sensitivity are the user's link inputs.

Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.

Field names used by the API: tx_power_dbm, tx_gain_dbi, tx_cable_loss_db, distance_km, frequency_mhz, rx_gain_dbi, rx_cable_loss_db, rx_sensitivity_dbm, eirp_dbm, rx_power_dbm, fade_margin_db

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