Patent ID: 7397249
Filing Date: 2008-07-08
Classification: G01V

Abstract:
1. For use in a region which contains at least first and second in-ground cables, each of which cables includes an electrically conductive component such that, when the first cable is driven at a locating signal frequency to emit a locating signal in an electromagnetic form, the locating signal can be coupled to the second cable in a way which causes the second cable to generate a false locating signal in electromagnetic form, as part of an overall apparatus for discriminating between the locating signal and the false locating signal, a transmitter, comprising: a frequency generator for generating said locating signal frequency; a phase shifter that is configured for receiving the locating signal frequency and subjecting the locating signal frequency to a given phase shift to produce a phase shifted locating signal frequency; an arrangement producing a reference signal and for impressing the phase shifted locating signal frequency thereon, to provide for distinguishing between the locating signal and the false locating signal and for transferring the reference signal; and a coupling configuration for coupling the locating signal frequency onto the first cable to generate the locating signal in a way which subjects the locating signal frequency to a coupling configuration phase shift such that the phase shifted locating frequency, as part of the reference signal subsequent to transfer thereof, can compensate for the coupling configuration phase shift of the locating signal frequency in the locating signal as emitted by the first cable.