| 摘要 |
An instrument for detecting the presence or absence of a buried pipe or cable employs three or more generally vertical coil aerials which define a triangular or polygonal area on the ground. The natural or induced electromagnetic radiation from any underground pipe or cable cutting that area gives rise to phase differences at the aerials which can be discriminated. The aerial array may be adjustable, and the discrimination may be direct or involve mixing the received signals. Facility for listening to various frequencies, perhaps simultaneously, can be provided.
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