Hello I want to make a WiFi hotspot in my house. I have an iMac (OS 10.5.8) and a Belkin N600 DB wireless N+ router. I have Google wifi delivered by a Cat-5 cable from an external antenna on my roof. The Belkin instructions are to connect the routers internet cable to the external modem. Problem is: I dont have an external modem, it is in the computer. How do I hook the router up? Do I need to buy an external modem?