In this document a methodology for the study interference between DTT and TVWS is described in order to automatize the process of channel assignation for TVWS devices through automatic calculus of propagation. This methodology defines the Protection Distance and Guard Band, introduces a relation between them and investigate some results based in Colombian typical scenarios through simulation and data analysis. Data shows that for DTT Colombian broadcast using modulation and coding rate 64QAM - 2/3 and a transmitted power of 64dBm, a TVWS device need at least 8.7km of separation if adjacent channel is allocated, but if the distance is 0Km at least 1.8MHz should be allocated.