My lrl theory

[FrancoItaly]

We know that a static E field exists above the ground, about 100V/m, I think that this field is not perfectly vertical but it's curved in south/north direction and this fact cause a not uniform field as an example at 1 meter above the ground. If we move our PD horizontally to 360 degrees we obtain some signals because the TR coil meets points of various intensity and this is the "compass" effect. The "sky" effect is similar at it's caused also by the vertical movement of the coil. Every unshielded TR coil is sensitive to static E field and this is the key of lrl phenomenon. A long buried metal generates a ground battery, a voltage difference between the target and all the ground in the vicinities and this acts also above the ground for some meters. A high degree of humidity lowers the "air impedance" and it reduces the signal from target. The signals of "compass" effect and long buried metals are very similar and a good system to null or reduces this effect it's a "differencial" approach and this is used in Alonzo PD: the ferrite coil supplies a 180 degrees signal mixed with omega coil and this reduces more the compass effect and less the long buried metals. If we increase the gain of PD the effect reappears.

Best Regards