Effective Radiated Power

ERP = Ptx × Gt

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Formula

ERP = Ptx × Gt

Description

Effective Radiated Power is the total power that would need to be radiated by an isotropic antenna to produce the same signal strength in the direction of maximum antenna gain. It combines the transmitter output power with the antenna gain to give a single figure of merit for the transmitting system. Regulatory agencies (FCC, ETSI) specify maximum ERP or EIRP limits for various frequency bands and applications. ERP uses a dipole reference while EIRP uses an isotropic reference (EIRP = ERP + 2.15 dB).

Variables

  • ERP — Effective radiated power (W)
  • Ptx — Transmitter output power (W)
  • Gt — Antenna gain (linear, not dB)

Practical Notes

Convert dBi gain to linear: Gt = 10^(GdBi/10). FCC Part 15 limits for 2.4 GHz ISM band: 1W conducted power with up to 6 dBi antenna gain (4W EIRP). Higher gain antennas require proportionally lower transmitter power to stay within limits. Cable losses between transmitter and antenna reduce ERP and must be accounted for.

Related Formulas

Wavelength Free Space Path Loss Signal-to-Noise Ratio Nyquist Sampling Rate Link Budget Antenna Gain

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