Calculate microwave point-to-point link feasibility from frequency, distance and antenna specs.
Free-space path loss (FSPL) is the signal attenuation that occurs simply from a radio wave spreading out over distance in an unobstructed path, with no absorption or reflection involved. The standard formula, FSPL(dB) = 20·log10(distance_km) + 20·log10(frequency_GHz) + 92.45, shows loss increases logarithmically with both distance and frequency — doubling either one adds a fixed ~6 dB of additional loss. This figure feeds directly into a full link budget (see the RF Link Budget or Wireless Link Budget calculators) to determine whether a given link will close with the available transmit power and antenna gains.
Free-space path loss
FSPL(dB) = 20·log10(distance_km) + 20·log10(frequency_GHz) + 92.45
Because the formula uses 20·log10(distance), and log10(2) ≈ 0.301, so 20 × 0.301 ≈ 6.02 dB — this holds regardless of the starting distance, which is why the 'doubling adds ~6 dB' rule of thumb is a constant, not distance-dependent.
The formula's frequency term behaves the same way as its distance term — 20·log10(frequency) — so doubling frequency also adds about 6 dB of loss, reflecting that a fixed-size antenna captures proportionally less of a shorter-wavelength wave's energy at a given range.
No — free-space path loss models only the geometric spreading loss in a vacuum/clear atmosphere. Higher-frequency microwave links (especially above ~10 GHz) need separate rain fade margin added to the link budget, since precipitation attenuation becomes significant at those frequencies.
Lower bands (6-11 GHz) suffer less path loss and rain fade, suiting longer links, but require larger antennas and face more spectrum congestion. Higher bands (23-38 GHz) support smaller, cheaper antennas and wider channels for higher capacity, but need shorter hops due to higher path loss and rain sensitivity.