| With the development of electronic technology,various electronic systems have been applied to many aspects of our daily life,and the adaptability of these electronic systems to the external electromagnetic environment is receiving more and more attention.Because of its transient high current and strong electromagnetic radiation pulse characteristics,natural lightning causes great harm to various electronic systems and people's lives and property.Therefore,lightning detection becomes an important task.Effective lightning detection has great practical significance for people to understand lightning mechanism and prevent lightning disasters.The VHF lightning electromagnetic wave receiving system in this subject based on the broadband characteristics of the dual-cone antenna is designed to detect lightning electromagnetic radiation.Based on the anti-jamming point of view,the working frequency of the VHF lightning electromagnetic wave receiving system studied in this paper is selected in the very pure cable television signal band,which is 270 MHz,and the frequency of the output signal is 38MHz.(1)According to the input impedance of the biconical antenna,the basic principle of the biconical antenna and the input impedance formula is obtained.According to the empirical formula of the electrical length of the dual-cone antenna and the signal wavelength and the input impedance of the antenna,the electrical length of the antenna is calculated to be 105.80 mm,and a prototype antenna is designed.Through the test of the S11 curve of the antenna,the size of the antenna is continuously adjusted.The actual length of the final vibrator is 100.00 mm.In the 0-350MHz frequency range,the antenna has only one center frequency,which is 268MHz,and the-lOdB bandwidth is in the range of 252MHz to 281 MHz.(2)The signal processing circuit is designed,including the design of the IF conversion circuit,the IF amplification circuit,and the follower.The TDQ-3B6S-C high-frequency cable tuner is used in this paper for VHF to mid-frequency 3 8MHz conversion to reduce the application of data acquisition,,storage,analysis and transmission pressure.Combining the automatic gain control characteristics of the MCl 350 mid-frequency amplifier chip,an intermediate frequency amplifier circuit is designed to amplify the IF signal output by the high-frequency cable tuner.Finally,all levels of circuits are soldered into circuit boards and static and dynamic debugging is performed.The debugging results show that the signal circuits work stably,and the output of the high-frequency cable tuner,intermediate frequency amplifying circuit,and follower are all 38 MHz,and the signal gain is about 60 dB.(3)The entire lightning electromagnetic wave receiving system is tested,including laboratory simulation tests and natural lightning measurements.The test results show that under the laboratory conditions,simulated lightning electromagnetic wave signals were not successfully received in only 2 times of 18 testing processes.That is,the detection efficiency of the receiving system to simulated lightning electromagnetic wave radiation sources is 88.9%,and the detection efficiency and the source radiation intensity is positively correlated;In the actual receiving of natural lightning electromagnetic wave test,the VHF lightning electromagnetic receiving system and the low-frequency magnetic antenna receive the lightning electromagnetic wave are with good synchronization,and the waveform richness is much higher than the low frequency magnetic antenna.The Fourier transform of the signal received by the VHF lightning electromagnetic wave receiving system shows that the signal intensity is at the maximum at a frequency of approximately 40 MHz,indicating that the collected signal is mainly near 40 MHz,and basically meets the design requirement. |
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