EIRP (Effective Radiated Power)
Calculate the equivalent isotropically radiated power (EIRP), EIRP = P_tx + G − L, adding the transmitter power P_tx (dBm) to the antenna gain G (dBi) and subtracting cable and connector losses L (dB). The result, in dBm, is the power a theoretical isotropic antenna would need to radiate to produce the same power density in the direction of the real antenna's maximum gain. It is the quantity regulated by telecom authorities (legal EIRP limits) and the transmit-side starting point of a link budget. Enter the transmitter power, the antenna gain and the losses.
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EIRP (effective radiated power)
EIRP (equivalent isotropically radiated power) answers a single question: in the direction my antenna points, how much effective power am I actually radiating? It combines the three transmit-side factors into one decibel sum: EIRP = P_tx + G − L, adding the transmitter power P_tx (dBm) to the antenna gain G (dBi) and subtracting the losses of cables, connectors and splitters L (dB). The result, in dBm, equals the power a theoretical isotropic antenna (one that radiates equally in every direction) would have to emit in order to match the power density that the real antenna, with its gain, produces along its boresight. EIRP matters for two reasons. First, it is the starting point of every link budget: propagation losses are subtracted from it to find the signal level at the receiver. Second, it is the regulated quantity: telecom regulators such as Anatel (the Brazilian telecommunications agency) and the FCC cap the maximum EIRP allowed in each band — which is why raising antenna gain forces you to back the transmitter power down to stay under the legal ceiling. Enter the transmitter power, the antenna gain and the losses.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.