RF Link Budget Calculator

This tool computes the end-to-end RF link budget in decibels (dB), including path loss, total gain, and received signal strength (RSSI). It also calculates fade margin—the safety buffer between received power and receiver sensitivity—to assess link reliability. Results help determine whether a wireless link will function reliably under given conditions.

It’s widely used for designing Wi-Fi networks, LoRaWAN and NB-IoT deployments, point-to-point microwave links, drone telemetry systems, and cellular small-cell backhaul. Engineers also use it during site surveys, regulatory compliance checks (e.g., FCC/ETSI), and troubleshooting intermittent connectivity issues in field deployments.

The calculator uses the free-space path loss (FSPL) model: FSPL (dB) = 20 log₁₀(d) + 20 log₁₀(f) + 32.45, where distance (d) is in km and frequency (f) is in MHz. While simplified, FSPL provides a solid baseline for line-of-sight scenarios; multipath or obstruction losses require additional margins.

Antenna gain (dBi) quantifies directional efficiency relative to an isotropic radiator. Typical values range from 0–3 dBi for omnidirectional PCB antennas, 6–12 dBi for sector or Yagi antennas, and up to 24+ dBi for parabolic dishes. Negative gains indicate lossy or poorly matched antennas and should be avoided in critical links.

Fade margin accounts for real-world impairments like multipath fading, foliage attenuation, rain (above 10 GHz), and temperature-induced refraction. A minimum of 10–20 dB is recommended for robust indoor or urban links; outdoor long-haul or mission-critical systems often require 25–30 dB. Insufficient margin leads to intermittent or dropped connections.

All inputs use standard RF engineering units: dBm for power, dBi for gain, MHz for frequency, and km for distance. Entering negative distance, zero/negative frequency, or extreme outliers (e.g., >1000 km at 2.4 GHz) may produce unrealistic path loss results—always validate assumptions against propagation models and environmental constraints.

No—it assumes ideal free-space propagation and does not model diffraction, reflection, or terrain effects. For NLOS scenarios, manually add appropriate path loss margins (e.g., +10–30 dB for urban canyons, +20–40 dB for dense foliage) or use specialized tools like ITU-R P.1411, COST-231, or ray-tracing simulators.

Received power (in dBm) indicates the signal level arriving at the receiver input. Compare it to your receiver’s sensitivity (e.g., −95 dBm for Wi-Fi, −130 dBm for LoRa). If received power exceeds sensitivity by ≥ fade margin, the link is viable. A result near or below sensitivity suggests poor reliability or failure.

dBi measures gain relative to an isotropic radiator; dBd references a dipole (0 dBd ≈ 2.15 dBi). This calculator expects dBi exclusively—using dBd without conversion will underestimate system gain by 2.15 dB per antenna, leading to overly optimistic range estimates.

Path loss increases with the square of frequency—doubling frequency adds ~6 dB loss. Higher frequencies (e.g., 5.8 GHz vs. 2.4 GHz) suffer greater atmospheric absorption, poorer diffraction around obstacles, and reduced penetration through walls. Hence, lower bands generally yield longer range and better NLOS performance for the same transmit power and antenna configuration.