DD Coil Issues With Shallow Targets

[Mike_Hillis]

I did some coil field mapping when I first got into the hobby.....actual coil fields look nothing like you think, especially close to the coil.   Dave and I had some conversations about it.   There is a reason for the air gap the mfg recommend on their coils and while minerals play into it, its also has a lot to do with the basic mechanics of the way the coil generates its magnetic fields.  

HH
Mike