Conducted vs Radiated RF Power in RAIN RFID
Configuring reader transmission power requires balancing maximum read distance against international electromagnetic spectrum regulations.
1. Radiated Power Equations
The total Effective Isotropic Radiated Power (EIRP) leaving the antenna face is:
EIRP (dBm) = P_Conducted (dBm) - L_Cable (dB) + G_Antenna (dBi)
2. Global UHF RFID Regulatory Comparison
| Jurisdiction | Frequency Range | Max Radiated Limit | Equivalent Watts |
|---|---|---|---|
| India (WPC) | 865.0 – 867.0 MHz | 4.0 Watts EIRP (36.02 dBm) | 4.0 W EIRP |
| USA (FCC Part 15) | 902.0 – 928.0 MHz | 4.0 Watts EIRP (36.00 dBm) | 4.0 W EIRP |
| Europe (ETSI Upper) | 865.6 – 867.6 MHz | 2.0 Watts ERP (35.15 dBm EIRP) | ~3.28 W EIRP |
| China (SRRC) | 920.5 – 924.5 MHz | 2.0 Watts ERP (35.15 dBm EIRP) | ~3.28 W EIRP |
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Frequently Asked Questions
What is the difference between EIRP and ERP?
EIRP (Effective Isotropic Radiated Power) measures radiated power relative to a theoretical isotropic antenna (in dBi). ERP (Effective Radiated Power) measures radiated power relative to a half-wave dipole antenna (in dBd). The conversion formula is EIRP (dBm) = ERP (dBm) + 2.15 dB.
What are the legal power limits for UHF RFID in India?
India WPC (Wireless Planning and Coordination) permits UHF RFID operation between 865.0 MHz and 867.0 MHz with a maximum radiated power limit of 4.0 Watts EIRP (36.02 dBm). Equipment must obtain ETA (Equipment Type Approval) certification.
Why do European ETSI rules use ERP instead of EIRP?
ETSI EN 302 208 specifies maximum limits using ERP (2.0 Watts ERP = 33 dBm ERP, which equals 35.15 dBm EIRP / ~3.28 Watts EIRP) to harmonize with European CE radio standards.
How do I convert conducted dBm power into Watts?
The conversion formula is Watts = 10^((dBm - 30) / 10). For quick reference: 30 dBm = 1.0 Watt, 33 dBm = 2.0 Watts, and 36 dBm = 4.0 Watts.