In order to extract usable harmonics from real 2n sequence pseudo-random data, a technical method is proposed. An equation for predicting the average amplitude of the main frequencies is proposed to guide the choice of signal type for different exploration tasks. By the threshold of the amplitude of the transmitted signal, a set of candidate frequencies are first selected. Then, by operating a spectrum envelope method at these candidate frequencies on received data, effective components in data are extracted. A frequency density calculation method is proposed based on a logical number summation method, to reasonably characterize the frequency density in different frequency bands. By applying this method to real data in Sichuan, China, with signal Type 13, 75 effective components are extracted, including both main frequencies and harmonics. The result suggests that the number of effective frequencies in the 2n sequence pseudo-random signal can be increased by extracting usable harmonics, without any additional fieldwork.
electromagnetic prospecting2n pseudo-random signalenergy conservationharmonic extractionfrequency density
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