Close a point-to-point wireless link: free-space path loss, received signal level, EIRP and the fade margin left over.
Free-space path loss grows 6 dB for every doubling of distance and 6 dB for every doubling of frequency. Adding transmitter power and antenna gain, then subtracting every loss along the path, gives the level arriving at the receiver; the difference from its sensitivity is the fade margin. A link that closes with 3 dB of margin works on the day you commission it and drops during the first heavy rain, so margin — not raw signal level — is the number that decides whether the hop is production-ready.
Point-to-Point Link
FSPL = 20·log10(d_km) + 20·log10(f_MHz) + 32.44; received level = Tx power + antenna gains − cable losses − FSPL − misc losses; fade margin = received level − sensitivity.
Regulatory EIRP
EIRP = transmit power + antenna gain − cable loss, which is the figure regulators cap.
FSPL = 20·log10(d_km) + 20·log10(f_MHz) + 32.44; received level = Tx power + antenna gains − cable losses − FSPL − misc losses; fade margin = received level − sensitivity. Free-space path loss grows 6 dB for every doubling of distance and 6 dB for every doubling of frequency. Adding transmitter power and antenna gain, then subtracting every loss along the path, gives the level arriving at the receiver; the difference from its sensitivity is the fade margin.
A link that closes with 3 dB of margin works on the day you commission it and drops during the first heavy rain, so margin — not raw signal level — is the number that decides whether the hop is production-ready.
This calculator takes 8 inputs: Link distance, Frequency, Transmit power, Transmit antenna gain, Receive antenna gain, Cable and connector loss per end, Rain, foliage and misc losses, Receiver sensitivity. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.