Online Tool Store
RF Link Budget Calculator
Calculate an RF link budget from transmit power, antenna gains, path loss, and receiver sensitivity, and see the margin that remains.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
RF link budget
Enter link parameters to get free-space path loss, received power, and margin.
Path loss
Received power
Margin
Margin above 10 dB is generally considered workable for a fixed link.
How the RF Link Budget Calculator works
- Enter frequency and distance to get the free-space path loss.
- Add transmit power, both antenna gains, and any cable and connector losses.
- Compare the received level to sensitivity — anything under about 10 dB of margin will not survive rain, foliage, or misalignment.
The method
A link budget is a sum in decibels: gains add, losses subtract, and the result is compared with what the receiver needs.
FSPL(dB) = 20log₁₀(d_km) + 20log₁₀(f_MHz) + 32.44; RX = TX + gains - losses
At 4 km and 5800 MHz: 12.04 + 75.27 + 32.44 = 119.8 dB, so 20 dBm plus 32 dBi of antenna gain lands at -67.8 dBm.
FAQ
How much margin is enough?
Ten decibels is a common minimum for a fixed outdoor link, and twenty is comfortable. Rain, foliage growth, and thermal drift all erode margin over the life of a link.
Does free-space loss cover everything?
No. It assumes clear line of sight with a clear Fresnel zone. Obstructions, ground reflections, and vegetation add losses that free-space maths does not predict.
Why does higher frequency mean more loss?
Because the effective aperture of an isotropic receiver shrinks with wavelength. It is not that the air absorbs more — it is a geometry effect, which is why higher-gain antennas recover it.
How we compare
| Feature | Online Tool Store | A graphing calculator | A stats package |
|---|---|---|---|
| Free-space path loss included | ✓ | Manual | Yes |
| Reports link margin | ✓ | Manual | ✓ |
| No licence or account | ✓ | ✓ | ✗ |
| Terrain and Fresnel modelling | ✗ | ✗ | ✓ |
RF Link Budget Calculator gives the clear-path figure and the margin — terrain, Fresnel clearance, and foliage are what turn a working budget into a failing link.