Abstract: A device that can reduce the effects of interference on an electromagnetic field emitted from a buried, underground or otherwise inaccessible object is provided. The device generates quality metrics relating to a plurality of sideband signals from one or more input signals, compares the quality metrics and selects one or more sideband signals, dependent on the respective quality metrics. A method of selecting one of a plurality of sideband signals using quality metrics is also disclosed.

Abstract: In order to locate an electrically conductive object, the electromagnetic field generated by a current in the object is detected by a detector having a plurality of spaced apart antennas. In order for the location of the object to be determined, two or more of the antennas together have at least four aerials, with first and second aerials measuring field components in a direction perpendicular to the direction of separation of the antennas, the third aerial measuring field components parallel to the direction of separation and the fourth aerial measuring field components in a direction mutually perpendicular to the field components measured by the first, second and third aerials.

Abstract: If a solenoid is mounted on an underground object, such as a boring tool, magnetic fields generated by an electric current flowing through that solenoid can be detected by a suitable detector at or above the surface. If the axis of the solenoid is tilted, the maximum value of the field is not directly above the solenoid. Therefore, the present invention makes use of measured values of horizontal and vertical components of the magnetic field to determine the separation of the detector and the solenoid, and also, by making use of a tilt sensor associated with the solenoid to derive a prediction of the ratio of the horizontal and vertical components of the field at a position vertically above or below the solenoid. If that predicted value of the ratio is then compared with the measured value of the ratio, the two will coincide when the detector is vertically above the solenoid. Thus, by moving the detector until such coincidence is obtained, the position of the solenoid can be determined.