Radio Link Budget dB

Radio Link Budget (dB)

A link budget tallies every gain and loss between transmitter and receiver, all in decibels: Pₕₓ (dBm) = Pₜₓ + Gₜₓ + Gₕₓ − FSPL − losses. Antenna gains count as positives; path loss, cables, connectors and atmospheric attenuation all subtract.

The term that usually dominates is the Free Space Path Loss (Friis): FSPL (dB) = 20·log₁₀(d) + 20·log₁₀(f) + 32.45, with distance d in km and frequency f in MHz. The full chain adds amplifiers, filters, connector and feedline losses, polarization mismatch and, on satellite links, atmospheric and rain attenuation. A solid design aims for a link margin of at least 3 dB above the receiver sensitivity.

Applications

Wi-Fi and 5G cell planning, satellite communication (LEO, GEO), microwave point-to-point links, IoT/LoRa coverage, broadcasting, amateur radio (HF/VHF/UHF), deep-space telemetry and tactical military networks all rely on it.

FAQ

Why use dB instead of linear units? In decibels, multiplicative gains and losses turn into additions, so the whole chain comes down to arithmetic, and the scale handles many orders of magnitude without trouble.

What is a reasonable link margin? At least 3 dB for terrestrial links. Satellite links usually want 6–10 dB to ride out rain fade, especially above 10 GHz.

How does frequency affect path loss? Double the frequency and you add 6 dB of FSPL over the same distance. That is why higher bands lean on more directive antennas or settle for shorter ranges.