This paper proposes a new propagation model to estimate the effect of multipath interference by 3D terrain and several on-channel repeaters (OCR) using ray tracing algorithm. If accurate terrain information data are given, the proposed model searches the path between transmitter and receiver using ray tracing algorithm, and calculates the path loss of each path applying multiple knife-edge (ITU-R), near-field ray approximation (Whitteker's) and heuristic UTD (Uniform Geometry Theory of Diffraction). The received field strength and delay profile can be obtained by summing all path to reach the receiver point. The received field strength and multipath interference, two essential element to decide DTV coverage, can be estimated by this analytic method to adapt ray tracing with comparative precision. By using this propagation model, we can estimate magnification or reduction of the coverage by OCR in DTV broadcasting, and seek the most compatible point of OCR
