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Attenuation of drill cables


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The frequency characteristics of a drill cable determines both the type of communication that can be used between a drill or logger and the surface, as well as the maximum rate of information that can be transferred. In order to revise the design, the attenuation of the cable was measured. The result was far from the characteristics of a coaxial cable. At medium audio frequencies, the attenuation was quite low. However at both low and high frequencies, the attenuation increased significantly, and the high frequency cut off could be approximated by a 3-order low pass filter with a cut off frequency of 8kHz. For comparison, the attenuation of a similar size coaxial type cable will be in order of 1dB/300m at 150kHz increasing to 2dB/300m at 1MHz. If a bandwidth higher than 10kHz is required for a 4km long oceanographic type electromechanical steel armoured cable, this has to be of coaxial construction with a shield separated from the armour.



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