A transparent free-space link-budget calculation for early RF planning and trade studies.
Open the RF link budget calculator in a full window
Version and review status
Formula set: v1.2
Staging review date: 17 August 2026
Status: Staging beta pending user acceptance and cross-browser checks.
Using this calculator
A transparent free-space link-budget calculation for early RF planning and trade studies.
Inputs and units
| Input | Unit or format |
|---|---|
| Frequency | GHz |
| Link distance | km |
| Transmitter power / receiver sensitivity | dBm |
| Transmit / receive antenna gain | dBi |
| Transmit / receive / additional losses | dB |
| Target margin | dB |
| Measured-noise comparison | on / off |
| Noise floor (when enabled) | dBm |
| Required SNR (when enabled) | dB |
Model and formula
The embedded RF app uses λ = 299792458 / frequency (Hz), FSPL = 20log10(4π × distance (m) / λ), EIRP = transmitter power + transmit gain − transmit loss, and received power = transmitter power + both antenna gains − FSPL − transmit, receive and additional losses. Margin = received power − effective threshold. With measured-noise comparison enabled, effective threshold is max(receiver sensitivity, noise floor + required SNR).
Worked example
At 5.8 GHz over 8 km, enter transmitter power 23 dBm, transmit and receive gain 24 dBi each, transmit and receive loss 1.5 dB each, additional loss 3 dB, sensitivity −75 dBm and target margin 20 dB; leave measured-noise comparison off. FSPL is 125.78 dB, EIRP 45.5 dBm and received power −60.78 dBm. Margin is 14.22 dB, so the 20 dB target is missed by 5.78 dB.
Interpreting the result
Received power above sensitivity does not mean the target margin is met. Sensitivity depends on the selected modulation, bandwidth and error criterion. Noise plus required SNR is a separate threshold; it is not added to sensitivity. This screen does not calculate availability, rain or gas attenuation, diffraction, interference statistics or regulatory authorisation.
Limits and verification
- Free-space loss does not include terrain, clutter, multipath, Fresnel obstruction, antenna orientation, polarisation mismatch, interference or atmospheric effects.
- Receiver sensitivity is modulation, bandwidth, data-rate and error-rate dependent.
- Check applicable spectrum, licensing and EIRP limits before transmission.
Worked examples checked against the calculator source on . These are reproducible calculation checks, not aircraft trials, site measurements or operational approval. Existing formula versions and technical review status remain as stated above.