the new razorback coils for minelab are a must have even though they are new to the market they have been tested and proven to out perform all others..you can get these on e bay under razorback coils if your interisted
just remember minelab will not work on your detector if you have a problem I just found this out straight from minelab as I wanted to do this to my extreme they said sorry if I mod the detector in any way iam outa luck if I need service
when I had my 4000 I was told while using a mono coil ro run the rx switch at dd. would get more depth then running in mono....now I have a gp extreme would I run the same way I guess its normal now on the extreme I would I use the setting e while running mono