RF Link Budget Documentation

The Friis transmission equation — baseline propagation loss for clear line-of-sight links. Formula: FSPL = 32.44 + 20·log₁₀(d_km) + 20·log₁₀(f_MHz).

Accounts for the direct path and ground-reflected path. Used for maritime, low-altitude, and over-flat-terrain links where ground reflection is significant.

Fresnel zone radius, earth bulge, and knife-edge diffraction loss. Determine minimum antenna height for 60% clearance and quantify obstacle-caused diffraction loss.

Effective Isotropic Radiated Power = Tx Power + Antenna Gain − Cable Loss. The starting point for every link budget and regulatory compliance check.

Fade Margin = Received Power − Receiver Sensitivity. The key link quality metric — shows how much headroom exists before the link fails. Target: ≥10 dB for outdoor links.

Convert RF power between dBm and watts. Includes formula, quick reference table, and common power level examples from GPS sensitivity to broadcast transmitters.

Minimum detectable signal level — computed from bandwidth, noise figure, and required SNR. Essential for link range calculations and radio selection.

Noise Figure quantifies receiver noise degradation above the thermal floor (−174 dBm/Hz). Noise Floor = −174 + 10·log₁₀(BW) + NF.

Shannon-Hartley theorem: C = N_s × B × log₂(1 + SNR). Theoretical maximum throughput for a given bandwidth and SNR — includes MIMO spatial multiplexing.

Cross-polarization mismatch loss between Tx and Rx antennas. Covers linear-linear, circular, and mixed polarization combinations — up to 30 dB isolation for cross-pol pairs.