RF Link Budget — Complete Guide

A link budget proves an RF path closes with adequate margin. It sums transmit power, antenna gains, and propagation losses, then compares the received signal level against receiver sensitivity. If the margin is positive the link works; if negative you must increase gain, reduce loss, or shorten the path.

Start with conducted Tx power in dBm, add antenna gain (dBi), subtract cable and connector losses (dB). The result is Effective Isotropic Radiated Power (EIRP). Validate every transmit chain with the EIRP calculator — even a 0.5 dB connector loss matters at long range.

FSPL = 32.45 + 20·log10(d_km) + 20·log10(f_MHz). This is the dominant loss term for most links. Compute it instantly with the free-space path loss calculator. For obstructed paths, check whether the first Fresnel zone is clear using the Fresnel zone calculator.

Receiver sensitivity floor = kTB + NF + required Eb/N0. The noise figure cascade calculator computes the cascaded NF and IIP3 of your entire receive chain from LNA through ADC. Reducing the first-stage NF by 1 dB improves sensitivity by nearly the same amount.

Link margin = received power − sensitivity. The link margin calculator accounts for atmospheric loss, rain fade (ITU-R P.838), and pointing loss. A margin under 10 dB is risky for fixed links; satellite and mobile links typically budget 20–30 dB.

The RF link budget calculator combines EIRP, FSPL, atmospheric loss, rain fade, pointing loss, and receive antenna gain into a single worksheet. Use the coax loss calculator to model feeder cable losses, and cross-check with the power density calculator for regulatory compliance.