Effective Radiated Power

The Effective Radiated Power (ERP) is the percieved power of an antenna along the direction of its gain. The Effective Isotropic Radiated Power (EIRP) is the same as the ERP, except that the gain is measured relative to isotropic antennas (dBi), while ERP measures gain relative to half-wave dipole antennas (dBd).

EIRP(dB) = ERP(dB) + 2.15 dB

Law

The limits are generally known as link budget.

India allows 4W ERP (36 dBm) in 2.4GHz and in 865-868 MHz. The tranmission power is 1W (30 dBm).

FCC allows 36 dBm EIRP for Point to Point (PtP) and 30 dB EIRP for Point to Multipoint (PtMP) connections.

In general, for every 1 dB lowered at the transmitter, the antenna gain can be increased by 3 dB.

Measurement of ERP

ERP(dbW) = $P_{TX}$ (dBW) - $P_{loss}$ (dB) + G(dBi) - 2.15 dB

EIRP(dbW) = $P_{TX}$ (dBW) - $P_{loss}$ (dB) + G(dBi)

Note: Antenna losses are included in the gain

How to convert dBm to Watts

Conversion formula:

dBm = 10*log10(mW) mW = 10^(dBm/10)

Typical values:

dBm	Watts		dBm	Watts		dBm	Watts
0	1.0 mW		16	40 mW		32	1.6 W
1	1.3 mW		17	50 mW		33	2.0 W
2	1.6 mW		18	63 mW		34	2.5 W
3	2.0 mW		19	79 mW		35	3.2 W
4	2.5 mW		20	100 mW		36	4.0 W
5	3.2 mW		21	126 mW		37	5.0 W
6	4 mW		22	158 mW		38	6.3 W
7	5 mW		23	200 mW		39	8.0 W
8	6 mW		24	250 mW		40	10 W
9	8 mW		25	316 mW		41	13 W
10	10 mW		26	398 mW		42	16 W
11	13 mW		27	500 mW		43	20 W
12	16 mW		28	630 mW		44	25 W
13	20 mW		29	800 mW		45	32 W
14	25 mW		30	1.0 W		46	40 W
15	32 mW		31	1.3 W		47	50 W

Additional Link factors

• Radiation angle (direction in degrees)
• Polarity (horizontal, vertical, circular)
• Beam width (In degrees)
• Fresnel Zone (Propagation path, an ellipsoidal region around the LoS; Important to check to decide if the channel will have a proper link)
• Link Budget = Power_TX + Gain_TX + Gain_RX + RX_Sensitivity – Path Loss
• Calculators
  • Fresnel Zone: https://www.everythingrf.com/rf-calculators/fresnel-zone-calculator