[mobilejdral]

If you mean ring type I don't remember which one worked best, sorry.

As for my favorite EM field there is a nearby street with buried powers lines and transformer boxes at ground level. As you walk the street to the main street each box has a bigger EM sphere and I like to let my hand coast over each sphere. It isn't a sphere per say, but only in the sense that at at certain depth in the field the density (for lack of a better term) becomes high enough that I can feel it and it is like a boundary line