An apparatus, method and program detect interference in cell sites of a wireless communications network. A cell site from the cell sites of the wireless communications network is selected and signal code power measurements from mobile devices in the cell site are received so that the sources of signals being transmitted to the mobile devices can be determined. Interfering sources are determined based on the signal code power measurements and the active set of sources for the mobile devices. The signal code power measurements are summed and ranked, and transmitters associated with the ranked signal code power measurements for the interfering sources are determined. The same procedure is repeated for all cell sites of the wireless communications network, and the transmitter that is an interfering source for the highest number of cell sites is selected as a problem transmitter.