Link Budget Calculator

The calculator only flags isLinkViable as true when link margin is strictly greater than 0 dB, so an exact 0 dB margin is reported as not viable. In practice a margin that thin offers no cushion at all against rain fade, multipath, or seasonal changes, so even a link the calculator does flag as viable at just 1-2 dB should be treated as marginal rather than reliable.

FSPL is calculated automatically from your entered distance and frequency using the standard 20·log10(d) + 20·log10(f) + 32.44 formula, representing loss from pure signal spreading in a vacuum. Additional Losses is a separate number you enter yourself to account for everything that formula ignores — rain fade, atmospheric absorption, multipath, or any other margin you want to budget for — and the two are simply added together before subtracting from EIRP.

EIRP represents the effective signal strength actually leaving your antenna — transmit power minus cable/connector loss up to the antenna, plus the antenna's own gain — and it's a fixed property of your transmit setup regardless of distance. Free-space path loss is then applied afterward because it depends on the specific frequency and distance to the receiver, so separating the two lets you see how much signal you're radiating before accounting for what the link to a particular receiver will cost you.

The calculator's viability flag only requires a margin above 0 dB, but the howToUse guidance and real-world planning both point to 10-20+ dB as a practical target. That headroom absorbs rain fade, seasonal foliage growth, multipath fading, and other real-world effects this simplified free-space model doesn't otherwise capture, so treat anything under about 10 dB as fragile even if the calculator marks it viable.