The FSPL equation describes an unobstructed path
For frequency in MHz and distance in km, FSPL = 32.44 + 20 log10(frequency) + 20 log10(distance). It describes geometric spreading in free space.
Higher frequencies lose more over the same distance
Doubling either frequency or distance adds about 6 dB of free space loss. Lower-band cellular signals therefore have a propagation advantage before other network-design factors are considered.
A real link budget needs more inputs
Buildings, terrain, foliage, diffraction, antenna patterns, polarization, transmit power and receiver sensitivity can dominate a real connection. FSPL is a baseline, not a coverage promise.
Frequently asked questions
What is the FSPL at 3.5 GHz over 1 km?
The ideal free space path loss is about 103.3 dB before antenna gain and environmental losses.
Does path loss mean the signal power is negative?
Path loss is a positive loss value in dB. Received power is found by applying losses and gains to transmitter power in a link budget.
Can FSPL predict cell tower coverage?
Not by itself. Cellular coverage also depends on antenna height and direction, terrain, buildings, spectrum, power and receiver performance.