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## EIRP vs ERP | difference between EIRP and ERP in LoRaWAN

This page compares EIRP vs ERP and mentions difference between EIRP and ERP used in LoRaWAN. It mentions purpose and relation between EIRP and ERP.

### EIRP

The EIRP is the short form of Effective Isotropic Radiated Power. It is the total power radiated by hypothetical isotropic antenna in a single direction.

EIRP can be expressed as follows. The unit of EIRP is dBm.

Where,
Transmit power is in dBm
Antenna gain is in dBi
Cable loss is in dB

Example (EIRP calculation) :
TxP = +20dBm , L = -5dB , Gt = +10 dBi
EIRP in dBm = +20 -5 + 10 = 25 dBm

### ERP

The ERP is the short form of Effective Radiated Power. It is the total power radiated by an actual antenna relative to a half wave dipole rather than a theoretical isotropic antenna.

The ERP calculation is similar to EIRP. It can be expressed as follows. The only difference is the antenna gain is expressed in dBd rather than dBi.

Example (ERP calculation) :
TxP = +20dBm , L = -5dB , Gt = +7.85 dBd
ERP in dBm = +20 -5 + 7.85 = 22.85 dBm

### Relation between EIRP and ERP

Following expression depicts relation between EIRP and ERP terms. As mentioned, EIRP value is 2.5 greater than the ERP.

### What is the purpose of EIRP and ERP

Both of these are essential requirements to be met by any electromagnetic (EM) or radio signal transmitting devices.
➨RF Transmitting systems should meet rules set by FCC and ETSI bodies.
➨Radio devices must not exceed certain EIRP and ERP values set by above bodies.