How EIRP is calculated. How to convert power in mW to dBm.
info@XtremeDevices.com - (204) 292-9724
Winnipeg, Manitoba - Canada
For each 3dB increase the power doubles.
For each 3dB decrease the power is halfed.
The following table provides an approximate conversion between dBm and mW.
| dBm | mW |
|---|---|
| 0dBm | 1mW |
| 3dBm | 2mW |
| 7dBm | 5mW |
| 10dBm | 10mW |
| 13dBm | 20mW |
| 15dBm | 30mW |
| 17dBm | 50mW |
| 20dBm | 100mW |
| 24dBm | 250mW |
| 27dBm | 500mW |
| 30dBm | 1Watt |
The radiated power is rated in either dBm or Watts. Power coming off an antenna is measured as Effective Isotropic Radiated Power (EIRP). EIRP is the value that regulatory agencies use to determine and measure power limits in applications such as 2.4GHz wireless equipment. EIRP is calculated by adding the transmitter power (in dBm) to the antenna gain (in dBi) and subtracting the cable loss (in dB).
For example:
100mW device = 20 dBm
50' LMR400 antenna cable has 3.4 dB loss
24 dB Grid Antenna has 24 dBi gain
The EIRP = 37.6 dBm (20 - 3.4 + 24)
The standards in North America are not to exceed an EIRP of 4Watts or +36dBm for 2.4GHz multipoint systems. Point-to-point systems may exceed this value if done properly.