EIRP vs. ERP: Key Differences Explained
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Let’s break down the difference between EIRP (Effective Isotropic Radiated Power) and ERP (Effective Radiated Power), two important concepts when dealing with radio frequency transmissions. Both relate to the power a transmitter radiates, but they use different reference points for antenna gain.
Here’s a summary of the major and minor differences:
- EIRP stands for Effective Isotropic Radiated Power.
- ERP stands for Effective Radiated Power.
The crucial difference lies in how antenna gain is measured:
- In EIRP calculations, antenna gain is expressed in dBi (decibels relative to an isotropic radiator).
- In ERP calculations, antenna gain is expressed in dBd (decibels relative to a half-wave dipole antenna).
This leads to a simple conversion:
- EIRP (in dBm) can be found by adding 2.15 to the ERP value (in dBm). This is because a half-wave dipole has a gain of approximately 2.15 dBi.
EIRP and ERP are not just theoretical concepts. Regulatory bodies use them to set limits for radio frequency transmitting devices across a variety of wireless technologies:
- These limits apply to indoor and outdoor wireless technologies such as GSM, LTE, 4G, 5G, LoRaWAN, and more.
To illustrate, here are the formulas for calculating EIRP and ERP:
Finally, a visual comparison:
In essence, both EIRP and ERP represent the effective power radiated by a transmitter, but they use different reference antennas (isotropic and half-wave dipole, respectively) for their calculations. Understanding this difference is key for complying with regulatory limits and optimizing wireless system performance.