The signals from VLF/LF transmitters are known to propagate in the Earth-ionosphere waveguide. so that the subionospheric propagation characteristics are very sensitive to the condition of the lower ionosphere. We know that there appear the terminator times just around the sunrise and sunset in the diurnal variation of subionospheric VLF/LF signal (amplitude and phase). These terminat... https://fitnessgravesyardes.shop/product-category/optical-speed-sensor/