CPC G01V 3/08 (2013.01) [G01V 3/12 (2013.01); G01V 3/165 (2013.01); G01V 3/17 (2013.01)] | 13 Claims |
1. A transmitter 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, said transmitter comprising:
a frequency generator configured to generate said locating signal frequency and to generate a reference signal, with said locating signal frequency impressed thereon;
a telemetry transmitter configured to transmit the reference signal as an electromagnetic reference signal; and
a coupler configured to couple the locating signal frequency onto the first cable such that detection of a phase shift between the locating signal and the false locating signal at a receiving location and based on the reference signal distinguishes the locating signal from the false locating signal.
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