Enter Link Values
Formula
FSPL(dB) = 20 log10(dkm) + 20 log10(fMHz) + 32.44
Higher frequencies and longer distances produce more free-space loss.
Worked Example
For a 2.4 GHz signal over 1 km:
FSPL = 20 log(1) + 20 log(2400) + 32.44 = 100.04 dB
A link budget must overcome that loss with transmit power, antenna gains, receiver sensitivity, and adequate margin.
Assumptions and Limits
Free-space loss assumes a clear line of sight and ideal spreading. Real links also include cable loss, antenna mismatch, polarization loss, obstruction, multipath, foliage, weather, and Fresnel-zone clearance.
Do not treat FSPL as a complete coverage prediction. Indoor and obstructed links can differ greatly from the free-space result.