On line measurement of partial discharges of equipment while in service has a great deal of potential in saving equipment down time in gas insulated substations (GIS) and gas insulated transmission lines (GITL). To address this aspect of partial discharge measurement there is scope for considerable progress particularly in the area of cables already is service. The laboratory measurement of high frequency current signals or emitted radio frequency signals is a relatively easier proposition than to measure PD in a cable that is already in service. One of the major constraints in on-line measurement of PD in cables is the attenuation in solid cables imposing a theoretical limitation to the PD measurement. The attenuation in a solid polythene cable has been numerically calculated and the effect of sheath is demonstrated.