ABSTRACT
The very low frequency (VLF) band of frequencies reveal useful details about the earth and is an important area of research. In this paper, VLF receiver is designed and fabricated to detect, monitor lightning strikes, and store this data as well as other emissions within the VLF band consisting of natural, and man-made VLF signals. A data acquisition system is designed and built which can receive signals in the VLF band. An antenna is built for the reception of VLF signals by winding 40 turns of 21 AWG copper wire on a wooden structure. A second order inductor-capacitor (LC) bandpass filter is designed with lower and upper cut off frequencies of ~700Hz and ~50kHz respectively. A pre-amplifier using the OP27 as the active amplifying component is used to amplify the filtered signal. The analog signal is digitized using the IQaudio Codec Zero soundcard HAT, which is attached to a Raspberry Pi 4B. The IQaudio Codec Zero soundcard acquires audio data at a sample rate of 96kHz and at a bit resolution of 24 bits. The Raspberry Pi runs the Raspberry Pi OS, which is an operating system based on the Linux Debian operating system. The Raspberry Pi runs a software tool package called vlfrx_tools which is made expressly for the processing, monitoring, and recording of VLF signals. Bash scripts are used to run the essential commands. The data stream is also passed via a local network and received by a program named Spectrum Lab, which runs on a Windows PC for more accurate processing and displaying of signals, if need be. The VLF receiver is intended to create awareness, educate society, and encourage further research about natural VLF radio, the geophysics and space science research fields.
