This article describes relevant information regarding the use of WiFi channels above 140 in Kerio Control NG100W and NG300W models; this information is pertinent to understand the reason for power loss (and hence issues with the strength of the signal and the general WiFi performance) for Kerio Control users in Germany, the Netherlands, and Bulgaria.
All WiFi devices, including client devices and broadband routers, communicate over specific wireless channels. Each WiFi channel is designated with a number that represents a specific radio communication frequency. The use of these channels is regulated by national laws that may vary from country to country.
Kerio Control NG100W and NG300W include a wireless package, which contains the wireless regulatory database used by the Central Regulatory Database Agent (CRDA) to configure wireless devices to operate within the radio spectrum allowed in the local jurisdiction. This package is common among Linux distributions.
In Germany, the Netherlands, and Bulgaria, it is illegal to use WiFi channels above 140, as they are limited to devices known as Short Range Devices (SRD); these SRD devices can cause interference to other wireless and radio equipment with a maximum transmit power of 25mW. Neither Kerio Control NG100W nor NG300W fall under this category.
As a consequence, when you set Kerio Control's channels above 140 in these countries, the transmit power reduces to 20mW to comply with these regulations. However, since you are using less energy, it is highly likely that you face issues with the strength of the signal and the general WiFi performance, which is why it is recommended that Kerio Control users from Germany, the Netherlands, and Bulgaria use channels below 140 for optimal power performance.
For additional information on WiFi channels in Kerio Control, refer to the following articles: