r is the series resistance component in the equivalent circuit model of a non ideal transmission line and g is the shunt conductance in the same model physically the r and the g arise due to completely different reasons r is due to the small yet finite resistivity in the non ideal metal conductor s of the line whereas g is due to the small yet again finite conductivity of the non ideal dielectric material between the metal conductor s of the line therefore in a lossless transmission line where the metal is a perfect conductor and the dielectric is a perfect insulator the metal exhibits no resistivity and the dielectric exhibits no conductivity hence the characteristic impedance of the lossless line reduces to z sqrt l c to look at it another way the non ideal metals and dielectrics that are used in transmission lines which is practically the case are the root cause of signal distortion but by implementing heaviside's condition distortionless transmission lines can be designed even with lossy materials note i keep using the terms lossy and lossless lossy simply means the transmission line has some r and or g associated with it and since any resistance when none is wanted or conversely any conductance when non is wanted results in loss of some of the energy of a signal a signal propagating through a lossy transmission line will lose some energy on the other hand a lossless i e perfect transmission line will cause no loss of signal energy