Study of VLF wave propagation at 12.3 kHZ – Preliminary results

Abstract

An experimental set-up consisting of a loop antenna, VLF tracking receiver, rubidium frequency standard for phase reference and two-channel strip chart recorder for recording the phase and strength of the incoming signals has been in operation at Rajkot since July 1991. The set-up is being used to monitor continuously the signal strength and phase of the 12.3 kHz VLF OMEGA signal from La Re-Union (20°58'S; 55°17'E). The data so far obtained show the typical diurnal variation of phase and amplitude. The diurnal phase change is typically 50 µs and the diurnal amplitude change is 14 dB which are found to vary from month to month. In addition, effect of solar flare is seen as a sudden decrease in phase by about 20 µs. Results of the analysis of amplitude and phase changes due to several flares are presented. Many abnormal features seen in the phase and amplitude records, such as periodic oscillations in the phase and amplitude, sudden spiky changes in amplitude and phase, fluctuations in phase alone but not associated with amplitude changes etc. are also presented.