Abstract: Apparatus is provided for modifying a conventional target locating system in which targets respond to an interrogation signal by transmitting a reply, and the target location is deduced from the azimuth from which a reply is received and the delay between the interrogation signal and the reply. The improvement includes a controllable attenuator coupling the receiving antenna to the target locating system which is controlled to selectively discriminate against selected range cells at selected azimuths. In a preferred embodiment, digital circuitry is relied upon to control the attenuator, and the identication of the range cells to be discriminated against is stored in a digital memory.