Free-Space Path Loss & Link Budget

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Free-space path loss (dB) from distance and frequency, and received power (dBm) from transmit power and antenna gains

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Enter the values

What to work out

Distance (d)

Frequency (f)

Result

Free-space path loss

120.04dB

Free space with a clear line of sight only — obstacles, rain, ground reflection and multipath are left out; real losses are usually higher.

Working

Formulas

Assumptions

Free space only: no obstacles, rain, atmospheric absorption, ground reflection or multipath.
The 32.44 constant is 20 log₁₀(4π × 10⁹ ÷ c), with d in km and f in MHz.
Antennas in each other's far field, facing each other, with matched polarisation.

Sources: ITU-R P.525 (calculation of free-space attenuation) · Friis transmission equation (H. T. Friis, Proc. IRE, 1946)

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