Varying Height And Azimuth?

[oldmancoyote1]

While experimenting with my Gold Racer, I think I saw more stable VIDs by raising the coil and scanning perpendicular to magnetic north. There seemed to be a height that was most stable, and scanning perpendicular to magnetic north tended to eliminate oscillation between very low and very high values.  It wasn't perfect, but it was suggestive.  I'm wondering if anyone else has anything to offer about this.

[Steve Herschbach]

Minelab pulse induction detectors in particular are susceptible to directional swing issues but it is not something normally encountered with a VLF. There is a scientific basis for what you are experiencing however.

Metal Detector Basics & Theory by Bruce Candy

See pages 12 and 13 and in particular the section on atmospheric sources of interference.