I would start off checking the range of your Base Station. Give this App a try: [https://itunes.apple.com/us/app/netspot-wifi-survey-wireless/id514951692?mt=12|NetSpot]. The other App I use is this one: [https://itunes.apple.com/us/app/wifi-signal/id525912054?mt=12|WiFi Signal] It will help in figuring out what is the best frequencies to use. One problem you can encounter is the AirPorts will try to daisy-chain to each other Vs connecting to your DLink Router. This is where you'll need to use the AirPort Utility to set different frequencies for the different AirPort units.