Geomagnetic Influence on Sky Wave Propagation of MF Signals

Abstract

The sky wave propagation of MF signals is provided by ordinary wave as the extraordinary wave is heavily absorbed. Hence, the efficiency with which this wave is excited determines the additional losses in this process and so the sky wave field at any distance. For any polarization of the incident wave, this efficiency is primarily a function of geomagnetic dip and the direction of propagation. A theoretical study of this aspect shows that in the case of vertical polarization, which is used for MF transmissions, the losses are abnormal in the case of E-W propagation at low latitudes as compared to N-S direction. The losses in N-S direction are in general small and do not vary much with latitude unlike losses in E-W direction. So these directional differences are comparatively small at higher latitudes. Experimental investigation of this phenomenon has been conducted recently in the Research Department of All India Radio at different latitudes and the results are in general agreement with theoretical expectations. The results of the above study are presented in this paper.