DocJohnson9, Yes mate i have been doing a lot of experimenting with large coils on the SPP. I tried to find my paper this morning for you which i wrote down the results. From memory doing air test with 18" commander mono coil, coil was ground balanced to the ground, Gain 10 and coil was laying on the ground and targets waved over the top of coil (This is the best way to do air tests IMO). A 5c coin 12" 50 c coin 16" $2 coin - 14" don't forget these were air tests, but i did do an in ground test with 5 cent coin and it was about right.