ERP
Understanding ERP
ERP and EIRP describe the same thing (effective radiated power) but use different reference antennas. ERP references a half-wave dipole (0 dBd); EIRP references an isotropic antenna (0 dBi). The choice depends on the industry and regulatory framework.
ERP vs EIRP
- ERP: Referenced to half-wave dipole. Used for broadcast (FM, TV), land mobile radio, and some older specifications.
- EIRP: Referenced to isotropic antenna. Used for satellite, microwave, and most modern specifications.
- Conversion: EIRP (dBm) = ERP (dBm) + 2.15 dB.
Regulatory Examples
- FM broadcast: Up to 100 kW ERP (80 dBm ERP = 82.15 dBm EIRP).
- Land mobile: Typically 50-500 W ERP.
- Wi-Fi: Specified in EIRP (36 dBm in US).
Frequently Asked Questions
What is ERP?
ERP is the effective radiated power referenced to a half-wave dipole antenna. ERP = TX power + antenna gain (dBd) - losses. Used primarily in broadcast and land mobile radio. EIRP = ERP + 2.15 dB.
When should I use ERP vs EIRP?
Use ERP for broadcast (FM, TV) and land mobile radio systems where regulations specify ERP. Use EIRP for satellite, microwave, and modern wireless systems. Always check which reference the applicable regulation uses.
Why do two different conventions exist?
ERP was established first for broadcast radio, where the half-wave dipole was the natural reference antenna. EIRP came later from satellite and microwave engineering, where the isotropic reference is more mathematically convenient. Both conventions persist due to legacy regulations.