Any of the current DD coils have different values in the receiver and transmitter coils, the higher impedance that the receiver exhibits unbalances the detectors cancellation function in cancel mode and causes a mismatch in the detector preamplifier stage resulting in less depth, greater noise pick up and increased responses to ground noise. DD coils if redesigned properly can be a game changer. i bet there will be new DD coils out in a couple of months. not by me..
