EIRP Calculator

A directional antenna does not create additional energy — it reshapes the radiation pattern so more of the existing power concentrates toward a preferred direction instead of spreading equally in all directions. EIRP measures the effective power in that strongest direction, so a higher-gain antenna raises EIRP even though the radio's actual transmit power output never changed.

Cable loss and connector loss are physically distinct sources of attenuation with different causes: cable loss accumulates continuously along the coax run's length, while connector loss is a fixed per-connection penalty from each mated pair. Tracking them separately lets you see which one dominates your system's losses and where an upgrade, shorter cable or better connectors, would help most.

47 CFR § 15.247 governs unlicensed intentional radiators using digital modulation or frequency hopping in the ISM bands. Its baseline limit is 1 watt (30 dBm) of conducted output power, which § 15.247(b)(4) requires be reduced once directional antenna gain exceeds 6 dBi — except under a narrow exception limited to fixed point-to-point links, which by rule excludes point-to-multipoint systems. Combining the 30 dBm power ceiling with the maximum unreduced 6 dBi of antenna gain gives 36 dBm, the practical EIRP ceiling this calculator checks for point-to-multipoint and other general 2.4 GHz configurations. Treat this as a starting reference and verify against the current text of § 15.247 for your specific device and configuration.

Regulatory text, radio datasheets, and link-budget spreadsheets don't consistently use the same unit — some quote dBm, others dBW, and antenna or system specs are sometimes given in linear watts. Providing all three lets you cross-check a single EIRP figure against whichever unit your reference document or regulation happens to use.