A simplified HF field strength prediction procedure for India

Field strength measurements of several HF broadcast transmissions were made at New Delhi during 1987-1990 with a view to evolving a simple procedure for estimation of the skywave field strength in the HF bands (3-30 MHz). An attempt has been made using the measured field strength values to arrive at a single combined loss factor which can account for all the losses in excess of basic free space and ionospheric absorption losses. The present study has shown that a provision of 4 dB for transmission losses other than free space and ionospheric absorption losses can bring the predicted values closer to measured field strength values for single-hop circuits in India for about 50% of the cases, and 10 dB increases it to 90%. Transmission losses in general were found to be much higher during equinoctial months in India, particularly around the peak region of equatorial anomaly