Hi 605400, welcome to the forums. I read somewhere, or I was told, that the actual FM antenna is inside the grey box, and only the location of the box should matter. However, in my experience also the location of the cable, leading from the box, affects signal strength received. When in my truck, I need to make sure the first one or two feet of the cable coming from the box can see through the window. Otherwise the FM signal strength will be 0 (zero), and it will just simply not work.