Radio link budget

Free-space path loss, received signal, and fade margin for a control or video link, with the transmitter's checked against the dated 2.4 GHz limit where you fly.

Planning and education aid. Not for primary navigation. Full disclaimer

Experimental: not yet fully verified. How results are checked

Computing your own values needs JavaScript and WebAssembly. The worked example below was computed when this page was built, and the documentation under "How we got this" applies.

114dB

The path loses 114 dB. The link keeps 0 dB of fade margin.

Beyond your 20 dBm EIRP limit (ETSI EN 300 328 V2.2.2 (2019-07), clauses 4.3.1.2.3 and 4.3.2.2.3, rules as of 2026-09-22) Against 47 CFR Part 15.

Received power
Fade margin
EIRP

Provenance

Computed by: drone.links.link-budget 1.0.1, core 0.1.0
Model: FSPL = 20 log₁₀ d_km + 20 log₁₀ f_MHz + 32.44 dB (ITU-R P.525); received power = transmit power + both antenna gains − cable losses − FSPL; fade margin = received power − sensitivity; EIRP = transmit power + transmit gain − half the cable loss, taken as the transmit side. 2.4 GHz limits from dated reference data
Accuracy: Free space only: terrain, the ground reflection, bodies, and vegetation add loss, so check the Fresnel zone and line of sight too. Planning aid; your equipment's certification governs
Notes: 1 shown with the answer
Cites: International Telecommunication Union, Recommendation ITU-R P.525-4: Calculation of free-space attenuation

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Your values

Showing an example. Change anything.

Frequency Like 2400 MHz · plain numbers mean MHz Distance Like 5 km · plain numbers mean km Transmit poweroptional Conducted, in dBm, like 20 · plain numbers mean dBm Receiver sensitivityoptional In dBm, like -90 · plain numbers mean dBm Rulesoptional us (47 CFR 15.247) or eu (ETSI EN 300 328), for the 2.4 GHz EIRP limit

More options 3

Transmit antenna gainoptional In dBi, like 2 (the default 0) · plain numbers mean dBi Receive antenna gainoptional In dBi, like 2 (the default 0) · plain numbers mean dBi Cable and connector lossesoptional Both ends together, in dB, like 1 (the default 0) · plain numbers mean dB

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How we got thisFormula, worked example, sources, and proof

Model: FSPL = 20 log₁₀ d_km + 20 log₁₀ f_MHz + 32.44 dB (ITU-R P.525); received power = transmit power + both antenna gains − cable losses − FSPL; fade margin = received power − sensitivity; EIRP = transmit power + transmit gain − half the cable loss, taken as the transmit side. 2.4 GHz limits from dated reference data

Show your work

Distance term
20 log₁₀ d_km
20 log₁₀ 5 = 13.98 dB
Free-space path loss
20 log₁₀ d_km + 20 log₁₀ f_MHz + 32.44
13.98 + 67.6 + 32.44 = 114 dB

The same steps an agent gets from the MCP server with explain: true.

Accuracy: Free space only: terrain, the ground reflection, bodies, and vegetation add loss, so check the Fresnel zone and line of sight too. Planning aid; your equipment's certification governs

Worked example: 2,400 MHz over 5 km, 20 dBm and 2 dBi each end, EU rules. Source: add-practitioner-essentials link scenario: FSPL about 114.0 dB at 2.4 GHz and 5 km. It is golden test vector v002, and every build checks the tool still gives its answer within its tolerance.

You enter

Distance: 5 km
Frequency: 2400 MHz
Rules: eu
Receive antenna gain: 2 dBi
Receiver sensitivity: -90 dBm
Transmit antenna gain: 2 dBi
Transmit power: 20 dBm

You get

Free-space path loss: 114 dB
Received power: -90 dBm
Fade margin: 0 dB
EIRP: 22 dBm
EIRP limit: Beyond your 20 dBm EIRP limit (ETSI EN 300 328 V2.2.2 (2019-07), clauses 4.3.1.2.3 and 4.3.2.2.3, rules as of 2026-09-22)

Review: Not yet independently reviewed by a Part 107 remote pilot.

Last verified: 2026-09-22, when a maintainer last confirmed this tool's sources at the issuer. See the sources ledger.

Status: version 1.0.1, core 0.1.0. See this tool in the verification report.

Changes

2026-09-23, fixed: Plain-number results in a fixed unit now show that unit: the battery current reads 9.7 A where it read 9.7, and decibels, gigabytes, pulses per square meter, grams per kilogram, nautical miles per gallon, hours, nanoteslas, and minutes now carry their units too. The numbers themselves do not change. Each tool's patch version went up. Changelog

Checked against: 5 golden test vectors (download the test vectors, each with its source and tolerance). See how results are checked and every source.

Sources

Recommendation ITU-R P.525-4: Calculation of free-space attenuation, International Telecommunication Union, P.525-4 (08/2019). Equation 6: L = 32.4 + 20 log f + 20 log d, with f in MHz and d in km.

Terms

CFR: Code of Federal Regulations: The codified US federal regulations. Aviation rules are in Title 14, written as 14 CFR. Source: 14 CFR Part 1 definitions
EIRP: effective isotropic radiated power: The power a transmitter and its antenna put out in their strongest direction, as if from an antenna that radiates equally everywhere; radio rules cap it. Source: 47 CFR Part 15
ETSI: European Telecommunications Standards Institute: The body that writes the European radio standards, such as EN 300 328 for 2.4 GHz equipment. Source: ETSI EN 300 328

Experimental means this tool has not yet met the stable bar: at least 20 golden vectors, differential tests, and an independent worked example.

EIRP — effective isotropic radiated power

The power a transmitter and its antenna put out in their strongest direction, as if from an antenna that radiates equally everywhere; radio rules cap it.

Source: 47 CFR Part 15