LoRaWAN gateways and end devices consist of radios (also called transceivers) that are capable of transmitting and receiving LoRa modulated radio signals. A radio needs an antenna to transmit or receive signals. The connection between the radio and the antenna is usually made by a piece of cable (for some devices it is a PCB trace). When transmitting, radio (transmitter) and antenna provide signal gain while antenna cable and connectors affect signal loss.
EIRP #
EIRP (Effective Isotropic Radiated Power) is the total power radiated by an isotropic antenna in a single direction. In this case, the antenna gain must be expressed in dBi.
The EIRP of a unit that consists of a transmitter, an antenna, and a cable can be calculated using the formula,
EIRP = Transmitter output power (dBm) + Antenna gain (dBi) - Cable loss (dB)
where the transmitter power in dBm, antenna gain in dBi, and cable loss in dB.
Question: Calculate the EIRP value of the following unit that consists of a LoRaWAN gateway, an antenna cable, and an antenna.
EIRP = Transmitter output power (dBm) + Antenna gain (dBi) - Cable loss (dB)
EIRP = 20 +3 -7 = 16 dBm
ERP #
Sometimes, the maximum output power is measured in ERP (Effective Radiated Power) instead of the EIRP.
ERP is the total power radiated by an actual antenna relative to a half-wave dipole antenna. In this case, the antenna gain must be expressed in dBd.
The ERP of a unit that consists of a transmitter, an antenna, and a cable can be calculated using the formula,
ERP = Transmitter output power (dBm) + Antenna gain (dBd) - Cable loss (dB)
where the transmitter power in dBm, antenna gain in dBd, and cable loss in dB.
ERP is also expressed in dBm.
Question: Calculate the ERP value of the following unit that consists of an end device, an antenna cable, and an antenna.
ERP = Transmitter output power (dBm) + Antenna gain (dBd) - Cable loss (dB)
ERP = 20 +0.85 -7 = 13.85 dBm
Conversion between EIRP and ERP #
You can easily convert EIRP to ERP and vice versa using the following equation:
EIRP (dBm) = ERP (dBm) + 2.15
Question: Convert the EIRP value 16 dBm to ERP.
ERP (dBm) = EIRP (dBm) - 2.15 ERP (dBm) = 16 -2.15 = 13.85 dBm
dBm to watts conversion #
EIRP or ERP values can be converted to watts (W) or milliwatts (mW), for example, EIRP 16 dBm is equivalent to 40 mW.
Read the section Rule of 10s and 3s in our guide dB, dBm, dBi and dBd to learn how to convert dBm to watts or milliwatts.
If you want to quickly convert dBm to watts or milliwatts without calculating by hand, an online tool is available at RapidTables
Regulations #
The maximum transmission power of a gateway or an end device is region specific and is regulated by the respective regulatory authorities. For example, in Europe, it is 25 mW ERP (+16 dBm EIRP) and is regulated by ETSI (European Telecommunications Standards Institute).
Read the LoRaWAN® Regional Parameters 1.0.3 to find the maximum allowed EIRP in other regions.
Adjust the following parameters to prevent EIRP/ERP/milliwatts thresholds from being exceeded.
- Transmitter output power
- Cable and connector attenuation
- Antenna gain