Development of a Microcomputer-Based Data Acquisition System for the SuperSID Monitor in the Philippines

The study of the changes in the behaviour of the Ionosphere is of great importance due to its influence on radio propagations. Stanford University's SuperSID monitor is used to study these changes by tracking the strength of very low frequency signals over time. The purpose of this research is to setup a SuperSID monitor in Manila, Philippines using a microcomputer as the main computing device. The Data Acquisition (DAQ) system includes a loop antenna, a preamplifier, a USB sound card, and a Raspberry Pi microcomputer. The system output is a SID data graph which is a plot of the relative VLF signal strength over time from NWC (19.8 kHz) and NDT (22.2 kHz) VLF transmitters. Pattern for the VLF signal strength during daytime was distinguished as more stable, compared to the fluctuations during night time. Also, the sunrise and sunset signatures were observed from the graph and were characterized as a gradual decay on VLF signal strength and as a sudden drop on VLF signal strength, respectively. To validate the signatures, it was compared to the actual civil twilight terminators over the monitor, the transmitter, and the midpoint or the center of minimum distance between the monitor (MIT-PH) and the transmitter. Based from the results, the minimum signal strengths from the SID graph correspond closely to the time when the civil twilight ends or starts over the midpoint of the monitor-transmitter pair.