tools / RF & SDR
Free-Space Path Loss Calculator
Work out the free-space path loss for a distance and frequency, and if you add a transmit power and antenna gains it gives you the received level at the far end too. Every link budget starts from this number, then you pile the real-world losses on top.
Doubling distance or frequency adds ~6 dB. Add TX power + gains to see the received level.
How it works
The equation
FSPL(dB) = 20·log10(d) + 20·log10(f) + 32.44, with distance in km and frequency in MHz. Double either the distance or the frequency and you add about 6 dB of loss.
Received power
Received power (dBm) = TX power + TX gain + RX gain minus FSPL minus cable losses. Compare it to the receiver sensitivity to see how much margin you have left.
FAQ
Does a higher frequency travel further?
With the same antennas, no. Path loss climbs with frequency, so higher bands lose more over the same distance. That is why long-range low-power links live down at 433, 868 and 915 MHz.
Is free space the same as real loss?
It is the best case, clear line of sight with nothing in the way. Terrain, trees and buildings add loss on top.
