Has anyone used the 10 1/2 inch dd coil how does it compare to the standard 9 inch concentric coil. I am only interested in using it for coin hunting. I have the standard coil on my machine but find it only covers a small area which would be lucky to be 6 inches across. I was thinking about buying the bigger coil but thought I would ask some peoples opinion of it first. thanks seeya Neilo