Originally Posted by richto
There is no EU law that restricts WiFi transmit power, so you can legally set whatever you want.
The only limit is on ERP, so you just need to use the power setting with an appropriate antenna....
In Europe at 2.4GHz we are limited by ETSI regulations to 20dbmW.
That is 20dB gain above 1mW or 100mW Effective radiated power compared to an isotropic (0 gain) aerial. This figure includes the gain from the aerial and losses from cabling.
So to calculate the EIRP of your system:
EIRP=Output power of card or access point in dBm – cable loss in dB – connector losses in dB + aerial gain in dBi
A typical card gives out +15dBmW so the largest aerial allowed is +5dB. However on a typical installation an +8dB aerial can be used as there is quite often a 3dB loss on the aerial cable.
The exception to the above is France, where the maximum output power is limited to 7dBm (5mW EIRP) at 2.4GHz.
Above from http://wireless.navigator.co.uk/index.htm
It's all slitting hairs unless some seriously directional antennas are going to be constructed,