New iMac WiFi problem

My new iMac have seriuos problems with the WiFi connection. Happens very often that I can't surf, but the connection from airport and my router is ok. Simply don't surf. Sometimes do it very frequently, and sometimes I can work for several hours. I have to turn off and turn on the airport to return to work fine. I have a Vodafone Station router. All my other devices works correctly (iPhone, pc, notebook) but the iMac not.

I tryed to change the WiFi channel but the problem persist. I tryed to eliminate a WEP and WPA, but the problem persist. I tryed to deactivate the DHCP and I assigned a static IP and DNS to my mac, but the problem persist. The WiFi signal is full.

Please help me.

Sorry for my english 😐