Just a brief post about some success in building a low cost internal antenna to replace the standard one - It won't give you amazing results, although as soon as I connected it, the number of aircraft went from 9 to 27 immediately, and I currently have 30 on the screen most days, it is mounted internally in the loft, although when the weather improves, it's going outside. The only other components was a 50ohm BNC lead I made. total distance between antenna and radardbox is about 5 ft.
http://www.maplin.co.uk/Module.aspx?ModuleNo=29613
http://www.maplin.co.uk/Module.aspx?ModuleNo=1637
http://www.maplin.co.uk/Module.aspx?moduleno=218787
http://www.maplin.co.uk/Module.aspx?ModuleNo=32015
http://www.maplin.co.uk/Module.aspx?ModuleNo=226
Total cost was about £80
I have no affiliation with maplins !-
http://www.huntsradar.gofreeserve.com/Radarbox/RadarBoxScreenShot.gif