When to use: Use to calculate free space path loss (FSPL) — the signal attenuation due to distance in an unobstructed line-of-sight environment. This is the starting point for every RF link budget. Higher frequencies and longer distances result in greater path loss. Select a preset frequency or enter a custom value. The result feeds directly into the Link Budget Calculator. In-building applications should add penetration and shadowing losses on top of FSPL.