Microwave Link Calculator

A microwave link budget is fundamentally a bookkeeping exercise: add up every gain and subtract every loss between transmitter and receiver, then see how much margin is left. This calculator starts with free-space path loss using the standard 92.45 + 20·log10(frequency in GHz) + 20·log10(distance in km) formula, subtracts that (plus miscellaneous losses like waveguide, connectors, and radome) from transmit power and both antenna gains to get the received signal level. Fade margin — the headroom above the receiver's sensitivity threshold — is the single most important output, because it drives everything downstream: link availability is estimated from it using the Vigants-Barnett multipath model, a named unavailability formula widely used in microwave link engineering, which scales unavailability with a climate/terrain factor, frequency, distance cubed, and an inverse-exponential function of fade margin in dB.

That cubic distance dependence means link length matters far more to reliability than frequency does, and it's why longer hops need disproportionately more fade margin to hit the same availability target. The calculator also reports the first Fresnel zone radius at path midpoint (used to judge line-of-sight obstruction clearance — you generally want 60%+ of this radius clear of obstacles) and a rain attenuation estimate built on the same power-law form ITU-R Recommendation P.838 uses for specific attenuation (attenuation = k × rain-rate^alpha, with frequency-dependent k and alpha) — simplified here to a fixed 25mm/hr moderate rain rate rather than P.838's full frequency- and polarization-dependent coefficient tables, since that becomes the dominant loss term at higher frequencies (above roughly 15 GHz). Because this rain estimate uses one fixed rain rate and simplified coefficients rather than ITU-R P.838's published tables and a region-specific ITU rain zone, treat availability and rain-attenuation numbers as planning-stage estimates, not the final design input for a licensed microwave path — that still needs a proper regional rain-zone lookup and vendor path-profile software.