EIRP (Equivalent Isotropically Radiated Power)
EIRP expresses effective radiated power relative to an isotropic antenna reference and is converted to ERP by the relation EIRP(dBm) = ERP(dBm) + 2.15. In the 2.4 GHz ISM band the upper limit under ETSI EN 300 328 is defined as 20 dBm (100 mW) EIRP; for wideband modulations other than FHSS a spectral density limit of 10 dBm/MHz additionally applies.
EIRP and ERP describe the same physical quantity with two different references. The confusion arises because the EIRP value of the same system always looks 2.15 dB larger than its ERP.
- Calculation: EIRP(dBm) = transmitter output power − cable loss + antenna gain (dBi).
- Example: a 14 dBm output, 1 dB of cable loss and a 2 dBi antenna give 15 dBm EIRP.
- Which is used in which band: sub-GHz short range device limits are generally in ERP, 2.4 GHz limits in EIRP.
Mixing up the unit when assessing a limit produces a systematic error of 2.15 dB; in a design working at the compliance limit this can make the difference between pass and fail. These values belong to the band and to the legislation. The output power of AXI's ST, SF and SAROZ sets is separately declared in the technical documentation, and band limits are not directly attributed to the product.
Context in which this term is used: Wireless remote control installation: pairing, relay, safety