Radio Link Budget Calculator
Calculate the link budget of a radio link in dB by adding transmit power and gains, then subtracting path losses. Useful for radio communication projects.
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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.
Related Tools
Free Space Path Loss (FSPL)
Calculate the free space path loss (FSPL), L = 20·log₁₀(d) + 20·log₁₀(f) + 32.44, from the distance d (km) and the frequency f (MHz). The result, in dB, is the attenuation a radio signal suffers simply by spreading through space, with no obstacles — proportional to the square of distance and frequency. It is the central term of any link budget: the greater the distance or frequency, the higher the loss and thus the more power or antenna gain needed. The 32.44 constant applies for km and MHz. Enter the distance and the frequency.
Fade Margin
Calculate the fade margin, M = P_rx − S, subtracting the receiver sensitivity S (dBm) from the received power P_rx (dBm). The result, in dB, is the slack between the arriving signal and the minimum the receiver can demodulate — the reserve available to absorb temporary fades caused by rain, multipath, vegetation and atmospheric variations. Reliable links typically require margins of 10 to 30 dB, depending on the desired availability and environment. It is the final check of a radio link budget. Enter the received power and the receiver sensitivity.
EIRP (Effective Radiated Power)
Calculate the equivalent isotropically radiated power (EIRP), EIRP = P_tx + G − L, adding the transmitter power P_tx (dBm) to the antenna gain G (dBi) and subtracting cable and connector losses L (dB). The result, in dBm, is the power a theoretical isotropic antenna would need to radiate to produce the same power density in the direction of the real antenna's maximum gain. It is the quantity regulated by telecom authorities (legal EIRP limits) and the transmit-side starting point of a link budget. Enter the transmitter power, the antenna gain and the losses.
Radio Band C Frequency
Convert wavelength to frequency (GHz) within the radio C band (4 to 8 GHz). Useful for satellite communication, radar and telecommunications.
Radio Band L Frequency
Converts wavelength to GHz inside L band (1-2 GHz) for radio astronomy.
Radio Band S Frequency
Convert wavelength to frequency (GHz) within the radio S band (2 to 4 GHz). Useful for radar, satellites, Wi-Fi and telecommunications.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.