Spectrum available and rules differ around the world
Q: What difference does the country code setting on my Access Point (AP) make?
A: The amount of spectrum available and the rules for using the spectrum differs between different regions of the world. For example, in the United States, we have 79MHz of spectrum available in the 2.4GHz band and can transmit up to 1 watt. In most of Europe, they have allocated more spectrum but the maximum transmit power is lower at just 100 milliwatts.
Setting the correct country code when you configure your Wi-Fi Alliance certified AP will ensure that the spectrum you use and the transmit powers are within the legal limits. Remember that if you install an external antenna with a greater gain, you'll need to adjust the power level on the AP to ensure that you are still within the regulation emission limits in your country.