Hilly terrain LOS fadeouts and Fresnel zone considerations from ray tracing techniques

The Tiruttani-Tirupati communication link situated in hilly terrain operating in line of sight (LOS) mode at 7 GHz suffers severe fadeouts during early hours of the day in the months of February and March. To investigate if the fadeouts are due to insufficient obstacle clearance along the entire propagation path, an attempt has been made to determine whether the first Fresnel zone clearance is secured under varied atmospheric conditions. A computer program has been developed rising the ray tracing technique to trace the path of the radio ray under varied meteorological situations encountered during the early hours of the day when generally the fadeouts are observed in the microwave link. It is revealed that the fadeouts observed are due to insufficient clearance at the hill top usually during subrefractive conditions.