The transfer function of electrical power lines for Broadband Power Line Communication (BPLC) is investigated through a signal-flow graph analysis. The work intends to present a new, simple and didactic way to model the transfer function of a multi-path model, in which the attenuation losses are taken into account. The results are compared to the transfer function obtained by the ABCD model. Measurements on coax cables and electrical grids are presented and the results are investigated.