Radiodetection Limited

Alasdair McPhee

Richard William Fling

Luigi Lanfranchi

Nicholas C Hillman

Transmitted magnetic field signals useable for locating an underground object, and methods and systems for generating the same. The magnetic field signal has desired spectral characteristics. More specifically, the transmitted magnetic field signal includes a carrier component useable for locating an underground object. The carrier component has a carrier component frequency substantially equal to an integer multiple of 300 Hz. This guarantees that the carrier component frequency is substantially equal to an integer multiple of both 50 Hz and 60 Hz. Such a carrier component allows use of maximum information sidebands in environments that often include harmonically derived interference signals at regular 50 Hz (&#xb1;0.1 Hz) or 60 Hz (&#xb1;0.1 Hz) intervals caused by power lines. The transmitted magnetic field signal may also include at least one information sideband including sideband energy. A substantial portion of the sideband energy is contained between the carrier component frequency and a frequency spaced 50 Hz from the carrier component frequency.

Method and system for producing a magnetic field signal usable for locating an underground object

Methods and systems for producing an encoded information signal having attenuated low frequency spectral components and a substantially constant average energy. An M bit code word is produced for each N bits of an information signal according to the following conditions: (a) each code word includes an equal number of logic zero bits and logic one bits; (b) each code word includes no more than two consecutive identical bits; and (c) M is greater than N. For example, M equals eight and N equals four. Such an encoded information signal is especially useful for generating a magnetic field signal usable for locating an underground object. This is in part because information sidebands of the magnetic field signal to have desired spectral characteristics that are useful in environments that often include harmonically derived interference signals at regular 50 Hz (&#xb1;0.1 Hz) or 60 Hz (&#xb1;0.1 Hz) intervals caused by power lines.

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Alasdair McPhee