Hi John, the simple answer is the longer the cable, the more attenuation to the signal! 15m of a heavy co-ax may cause less loss/attenuation than 5mA thin one. A lightweight co-ax will cause more loss than a great thick heavy one, but the thicker one will be much stiffer and doesn't like tight curves. Connectors fitted to the box end of the cable can stop you threading the cable through a hole. Personally, I'd always go for a thin, flexible 150mm "patch" lead from the heavy downlead to the box. Plenty of posts in here to different makes/specs of cable - search for Westflex, Ecoflex, Garex.