The buried metal pipelines laying environment is complicated.During the pipeline positioning procedure,it is imperative for the receiver to effectively separate the 128 Hz positioning signal from the multi-frequency signals emitted by the pipeline,and eliminate the high-frequency signals and 50 Hz power frequency signal.According to the practical demands of buried pipeline inspection,nine types of fourth-order 128 Hz narrow-band pass filters with distinct topologies were designed and simulated using Multisim 14.The results indicate that filters of the same topology have similar amplitude-frequency characteristics,and the input-output gain is slightly different.The central frequency of the 9 filters is about 128 Hz.The 1 dB Chebyshev MFB filter has the narrowest bandwidth(36.803 Hz)and highest Q value(3.473).Further simulation indicate that the filter can efficiently extract the 128 Hz signal and eliminate interference signals,which reduced the noise below 0.132 μV·Hz-1/2 within the-3 dB bandwidth frequency range(i.e.108-145 Hz).Moreover,the filter demonstrates strong stability and shows slight variations in amplitude-frequency characteristics when subjected to changes in temperature and capacitance tolerance.
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