A study of HF field strength variation in India and its prediction

Measured field strength data pertaining to several HF broadcast transmissions monitored in India during 1987-90 has been analysed to study solar activity, local time and seasonal variations in the field-strength. Values tend to saturate at high solar activity levels when sunspot numbers are beyond 120. Variations in field strength have also been studied with varying ratios of operational frequency to maximum usable frequency (f_op/MUF) and equivalent vertical frequency of the links. Based on this study a prediction method for HF field strength has been suggested for India. Comparison of values estimated using this technique has been made with actual measured field strength values for different HF transmissions for different months. This method is to be particularly suitable for field operators